diff --git a/benchmarks/runtime/README.md b/benchmarks/runtime/README.md
index d14e4c10d..c69ec43d9 100644
--- a/benchmarks/runtime/README.md
+++ b/benchmarks/runtime/README.md
@@ -31,6 +31,7 @@ Application-shaped workloads for measuring the speed of compiled executables. Ea
 | `regex-logs` | cpu | regex `exec` with groups, `test`, global `replace` |
 | `region-builds` | cpu | a watch-mode build loop over `LifetimeRegion`: each build binds a program in a new region and releases the previous one, which a cache keeps referenced for two builds |
 | `template-render` | cpu | template literals, escaping, `map`/`join` |
+| `throw-chains` | cpu | exceptions caught 2, 5 and 20 recursive calls above the throw, through direct calls and through a callback, and a backtracking parser that throws on a failed alternative |
 | `thread-slots`, `thread-slots-cache` | cpu | worker threads reading one published type graph from an `InternTable` and keeping per-thread state for each type they visit: a `ThreadSlots` family, or a direct-mapped cache by id in front of a `Map` by id (the `-cache` entry); under Node.js both are per thread |
 | `typed-array-kernels` | cpu | element-wise loops that run to one typed array's length and index others at the same position: `Float64Array` axpy, `Float32Array` blend, `Uint8Array` mask, wrapping `Int32Array` add, `Uint8ClampedArray` brighten, RGBA to gray, a row-major `Float32Array` matrix-vector product, and `reduce`/`some`/`map` callbacks |
 | `typed-array-scan`, `typed-array-scan-workers` | cpu | element-by-element scan loops over `Uint8Array`, `Uint16Array`, `Int32Array` and `Float64Array`; the second entry is a worker-enabled executable (it can start a worker), so each access also checks for shared storage |
diff --git a/benchmarks/runtime/workloads/throw-chains.json b/benchmarks/runtime/workloads/throw-chains.json
new file mode 100644
index 000000000..79cf5ea87
--- /dev/null
+++ b/benchmarks/runtime/workloads/throw-chains.json
@@ -0,0 +1,6 @@
+{
+  "entry": "workloads/throw-chains.ts",
+  "args": [
+    "1"
+  ]
+}
diff --git a/benchmarks/runtime/workloads/throw-chains.ts b/benchmarks/runtime/workloads/throw-chains.ts
new file mode 100644
index 000000000..c96816aed
--- /dev/null
+++ b/benchmarks/runtime/workloads/throw-chains.ts
@@ -0,0 +1,196 @@
+// Exceptions that cross many frames: throws from helpers below a recursion,
+// caught 2, 5 and 20 recursive calls up (direct calls, then calls through a
+// callback), with each frame holding an array across its call, and a
+// backtracking parser that uses exceptions for control flow.
+class ParseError extends Error {
+  readonly at: number;
+  constructor(at: number, message: string) {
+    super(message);
+    this.at = at;
+  }
+}
+
+/** A thrown value that is not an Error (no stack to capture). */
+class Stop {
+  readonly code: number;
+  constructor(code: number) {
+    this.code = code;
+  }
+}
+
+const held: number[][] = [];
+function fail(n: number, plain: boolean): number {
+  if (plain) throw new Stop(n);
+  throw new RangeError("chain " + n);
+}
+function check(n: number, plain: boolean): number {
+  return (n & 3) === 0 ? fail(n, plain) : n;
+}
+function validate(n: number, plain: boolean): number {
+  return check(n, plain) + (n & 1);
+}
+function bottom(n: number, plain: boolean): number {
+  const box = [n, -1];
+  const r = validate(n, plain);
+  held[0] = box;
+  return r + box.length;
+}
+function walk(n: number, depth: number, plain: boolean): number {
+  const box = [n, depth];
+  const r = depth === 0 ? bottom(n, plain) : walk(n, depth - 1, plain);
+  held[depth] = box;
+  return r + box.length;
+}
+
+function chains(rounds: number): string {
+  const out: string[] = [];
+  for (const depth of [2, 5, 20])
+    for (const plain of [false, true]) {
+      let caught = 0;
+      let sum = 0;
+      for (let i = 0; i < rounds; i++) {
+        try {
+          sum += walk(i, depth - 2, plain);
+        } catch (error) {
+          caught++;
+          sum += error instanceof Stop ? error.code & 7 : 1;
+        }
+      }
+      out.push(`depth ${depth} ${plain ? "object" : "error"}: caught ${caught} sum ${sum}`);
+    }
+  return out.join("\n");
+}
+
+// The same chains through a callback: each level visits the next with a
+// closure, as tree visitors do.
+function visit(n: number, depth: number, each: (n: number, depth: number) => number): number {
+  const box = [n, depth];
+  const r = depth === 0 ? bottom(n, false) : each(n, depth - 1);
+  held[depth] = box;
+  return r + box.length;
+}
+function visits(rounds: number): string {
+  const out: string[] = [];
+  const each = (n: number, depth: number): number => visit(n, depth, each);
+  for (const depth of [2, 5, 20]) {
+    let caught = 0;
+    let sum = 0;
+    for (let i = 0; i < rounds; i++) {
+      try {
+        sum += visit(i, depth - 2, each);
+      } catch (error) {
+        caught++;
+        sum += error instanceof RangeError ? 1 : 0;
+      }
+    }
+    out.push(`visit depth ${depth}: caught ${caught} sum ${sum}`);
+  }
+  return out.join("\n");
+}
+
+// expr := term (("+" | "-") term)*; term := atom ("*" atom)*;
+// atom := number | "(" expr ")" | name "(" expr ("," expr)* ")" | name.
+// A call and a name start alike: the parser tries the call first and
+// backtracks when it fails.
+let text = "";
+let pos = 0;
+function peek(): string {
+  return pos < text.length ? text[pos]! : "";
+}
+function expect(c: string): void {
+  if (peek() !== c) throw new ParseError(pos, `expected ${c}`);
+  pos++;
+}
+function name(): string {
+  const start = pos;
+  while (pos < text.length && text.charCodeAt(pos) >= 97 && text.charCodeAt(pos) <= 122) pos++;
+  if (pos === start) throw new ParseError(pos, "expected a name");
+  return text.slice(start, pos);
+}
+function call(): number {
+  const callee = name();
+  expect("(");
+  let value = expr() + callee.length;
+  while (peek() === ",") {
+    pos++;
+    value += expr();
+  }
+  expect(")");
+  return value;
+}
+function atom(): number {
+  const c = peek();
+  if (c >= "0" && c <= "9") {
+    let value = 0;
+    while (peek() >= "0" && peek() <= "9") value = value * 10 + (text.charCodeAt(pos++) - 48);
+    return value;
+  }
+  if (c === "(") {
+    pos++;
+    const value = expr();
+    expect(")");
+    return value;
+  }
+  const start = pos;
+  try {
+    return call();
+  } catch (error) {
+    if (!(error instanceof ParseError)) throw error;
+    pos = start;
+    return name().length;
+  }
+}
+function term(): number {
+  let value = atom();
+  while (peek() === "*") {
+    pos++;
+    value = (value * atom()) % 1000003;
+  }
+  return value;
+}
+function expr(): number {
+  let value = term();
+  while (peek() === "+" || peek() === "-") {
+    const op = text[pos++];
+    value = op === "+" ? value + term() : value - term();
+  }
+  return value;
+}
+
+let seed = 4242;
+function random(): number {
+  seed = (Math.imul(seed, 1103515245) + 12345) >>> 0;
+  return seed / 4294967296;
+}
+function source(depth: number): string {
+  const r = random();
+  if (depth > 6 || r < 0.25) return String(Math.floor(random() * 100));
+  if (r < 0.45) return "abcdefgh".slice(0, 1 + Math.floor(random() * 8));
+  if (r < 0.6) return `(${source(depth + 1)})`;
+  if (r < 0.8) return `${source(depth + 1)}${random() < 0.5 ? "+" : "*"}${source(depth + 1)}`;
+  return `f${"xyz".slice(0, Math.floor(random() * 3))}(${source(depth + 1)},${source(depth + 1)})`;
+}
+
+function parse(count: number): string {
+  let total = 0;
+  let failed = 0;
+  for (let i = 0; i < count; i++) {
+    // Every tenth input lacks its last character, which fails deep inside it.
+    const full = source(0);
+    text = i % 10 === 0 ? full.slice(0, -1) : full;
+    pos = 0;
+    try {
+      total = (total + expr()) % 1000003;
+      if (pos !== text.length) throw new ParseError(pos, "trailing input");
+    } catch (error) {
+      if (!(error instanceof ParseError)) throw error;
+      failed++;
+    }
+  }
+  return `parsed ${count}: total ${total} failed ${failed}`;
+}
+
+const scale = Number(process.argv[2] ?? "1");
+console.log(chains(Math.floor(60000 * scale)));
+console.log(visits(Math.floor(60000 * scale)));
+console.log(parse(Math.floor(40000 * scale)));
diff --git a/packages/compiler/src/backend/llvm/blocks.ts b/packages/compiler/src/backend/llvm/blocks.ts
index 354e631c6..eee4d00b9 100644
--- a/packages/compiler/src/backend/llvm/blocks.ts
+++ b/packages/compiler/src/backend/llvm/blocks.ts
@@ -9,6 +9,7 @@
  * code after it); here the lines are DROPPED instead, and emitStmts skips
  * whole statements once the current block is terminated, so no dropped
  * definition can leak into a later block. */
+import { UNWIND_RESUME, UNWIND_SLOT } from "./unwind-abi.js";
 
 export class BlockBuilder {
   private readonly blocks: { label: string; lines: string[]; term: string | null }[] = [];
@@ -86,7 +87,18 @@ export class BlockBuilder {
 
   terminate(s: string): void {
     if (this.cur.term === null) {
-      if (this.returnEpilogue && s.startsWith("ret ")) this.line(this.returnEpilogue);
+      if (
+        this.returnEpilogue &&
+        (s.startsWith("ret ") ||
+          s.startsWith("call void @scr_unwind_raise()") ||
+          s === UNWIND_RESUME)
+      )
+        this.line(this.returnEpilogue);
+      if (s === UNWIND_RESUME) {
+        const exception = this.tmp();
+        this.line(`${exception} = load { ptr, i32 }, ptr ${UNWIND_SLOT}`);
+        s = `resume { ptr, i32 } ${exception}`;
+      }
       this.cur.term = `  ${this.withDebugLocation(s)}`;
     }
   }
diff --git a/packages/compiler/src/backend/llvm/emit-function.ts b/packages/compiler/src/backend/llvm/emit-function.ts
index 327d2019b..a3ebbe0e8 100644
--- a/packages/compiler/src/backend/llvm/emit-function.ts
+++ b/packages/compiler/src/backend/llvm/emit-function.ts
@@ -56,11 +56,14 @@ import { emitIntegerClone, emitIntegerDispatcher } from "./integer-clones.js";
 import { beginFunctionLoops, LOOPS } from "./loop-state.js";
 import { runningExtremumUpdates } from "./running-extrema.js";
 import { findIntegerOrNaNLocals } from "./wrapping-sums.js";
+import { UNWIND_PERSONALITY, UNWIND_SLOT } from "./unwind-abi.js";
 
 export function emitFunction(emitter: LlEmitter, fn: IrFunction): string {
   const B = new BlockBuilder();
   emitter.B = B;
   emitter.currentFunctionName = fn.name;
+  emitter.currentUnwindAbi = emitter.unwindAbi.has(fn.name);
+  emitter.usesLandingPads = false;
   emitter.findInt32Allocations(fn);
   emitter.currentTier = fn.tier;
   // Fiber switches restore the active exception cell before control
@@ -597,6 +600,8 @@ export function emitFunction(emitter: LlEmitter, fn: IrFunction): string {
     B.terminate(cleanup.terminator);
   }
 
+  if (emitter.usesLandingPads && emitter.currentUnwindAbi)
+    B.entryAllocas.push(`${UNWIND_SLOT} = alloca { ptr, i32 }`);
   if (emitter.logArgSlots > 0) {
     B.entryAllocas.push(`%logargs = alloca [${emitter.logArgSlots} x %ScrLogArg]`);
   }
@@ -637,7 +642,10 @@ export function emitFunction(emitter: LlEmitter, fn: IrFunction): string {
   const debug = emitter.debugScope === null ? "" : ` !dbg ${emitter.debugScope}`;
   const symbol = borrowed ? mangleBorrowedFunction(fn.name) : mangleFunction(fn.name);
   emitter.privateGlobalSlots.clear();
-  let body = `define internal ${ret} @${symbol}${int32Abi ? INT32_ABI_SUFFIX : ""}(${params.join(", ")}) ${attrs}${debug} { ; ${fn.name}\n${B.render()}\n}`;
+  // Landing pads (emitDirectCall) need the personality.
+  const personality = emitter.usesLandingPads ? ` ${UNWIND_PERSONALITY}` : "";
+  if (emitter.usesLandingPads) emitter.declare(`declare i32 @__gcc_personality_v0(...)`);
+  let body = `define internal ${ret} @${symbol}${int32Abi ? INT32_ABI_SUFFIX : ""}(${params.join(", ")}) ${attrs}${personality}${debug} { ; ${fn.name}\n${B.render()}\n}`;
   if (int32Abi) body += "\n" + emitter.emitInt32AbiWrapper(fn, symbol, int32Abi);
   if (emitter.integerClones.members.has(fn.name)) {
     body += "\n" + emitIntegerClone(fn, emitter, emitter.stackChecks?.has(fn.name) === true);
diff --git a/packages/compiler/src/backend/llvm/emitter.ts b/packages/compiler/src/backend/llvm/emitter.ts
index f6f9ea313..0243763f1 100644
--- a/packages/compiler/src/backend/llvm/emitter.ts
+++ b/packages/compiler/src/backend/llvm/emitter.ts
@@ -131,6 +131,16 @@ import {
   type FfiCallbackAdapter,
 } from "../ffi-callbacks.js";
 import { computeMayThrow } from "../may-throw.js";
+import {
+  UNWIND_PERSONALITY,
+  UNWIND_RAISE,
+  UNWIND_RAISE_DECLARATION,
+  UNWIND_RESUME,
+  UNWIND_SLOT,
+  UnwindAbiViolation,
+  bridgePlainUnwindCalls,
+  unwindAbiFunctions,
+} from "./unwind-abi.js";
 import {
   mangleAsyncInlineAwaitCall,
   mangleAsyncSpawn,
@@ -442,6 +452,12 @@ export interface ForkPrimitives {
 export interface LlvmTargetOptions {
   /** C ABI target; omitted direct emission uses the host ABI. */
   targetTriple?: string;
+  /** Linux (glibc and musl) executables: functions reached only by direct
+   * calls propagate exceptions by unwinding the native stack (unwind-abi.ts). */
+  unwindAbi?: boolean;
+  /** Functions kept on the pending-flag ABI under `unwindAbi`: the ones an
+   * earlier emission found breaking its rules (UnwindAbiViolation). */
+  unwindExcluded?: ReadonlySet<string>;
   /** Emit the function bodies in this many contiguous ranges, each by its
    * own emitter, and merge them in function order (emit-journal.ts). The
    * output is the same as one emitter's. Debug builds (`debugSources`)
@@ -595,16 +611,36 @@ function moduleEmitter(input: IrModule, options: LlvmTargetOptions): LlEmitter {
   return new LlEmitter(emitted, options, null, prepared?.mod === emitted ? prepared : null);
 }
 
+/** Emits the module's parts, emitting it again with the functions an
+ * UnwindAbiViolation names on the pending-flag ABI. */
+function emitModuleText(input: IrModule, options: LlvmTargetOptions): string[] {
+  for (let excluded = options.unwindExcluded ?? new Set<string>(); ;) {
+    const emitter = moduleEmitter(input, { ...options, unwindExcluded: excluded });
+    try {
+      return emitter.emitParts();
+    } catch (error) {
+      if (!(error instanceof UnwindAbiViolation)) throw error;
+      const names = new Set(excluded);
+      for (const name of emitter.unwindAbi)
+        for (const symbol of [mangleFunction(name), mangleBorrowedFunction(name)])
+          if (error.symbols.has(symbol) || error.symbols.has(symbol + INT32_ABI_SUFFIX))
+            names.add(name);
+      if (names.size === excluded.size) throw error;
+      excluded = names;
+    }
+  }
+}
+
 export function emitLlvmModule(input: IrModule, options: LlvmTargetOptions = {}): string {
-  return moduleEmitter(input, options).emit();
+  return emitModuleText(input, options).join("\n");
 }
 
 /** emitLlvmModule's text as parts that concatenate to it, without the copy
  * that joining them makes: a large program's text is 150 MB. */
 export function emitLlvmModuleParts(input: IrModule, options: LlvmTargetOptions = {}): string[] {
-  return moduleEmitter(input, options)
-    .emitParts()
-    .flatMap((part, index) => (index === 0 ? [part] : ["\n", part]));
+  return emitModuleText(input, options).flatMap((part, index) =>
+    index === 0 ? [part] : ["\n", part],
+  );
 }
 
 /** Keep large translation units below the host's single-string limit. */
@@ -614,7 +650,7 @@ export function emitLlvmModuleSource(
 ): string | readonly string[] {
   // IR validation, contracts and the frontend's disposal run after lowering without checks.
   relieveHeapPressure(true);
-  const parts = moduleEmitter(input, options).emitParts();
+  const parts = emitModuleText(input, options);
   const length = parts.reduce((total, part) => total + part.length, Math.max(0, parts.length - 1));
   if (length <= 256 * 1024 * 1024) return parts.join("\n");
   return parts.flatMap((part, index) => (index === 0 ? [part] : ["\n", part]));
@@ -1258,6 +1294,10 @@ export class LlEmitter {
   /** May-throw analysis (computeMayThrow): pending
    * checks are emitted only after calls that can actually raise. */
   readonly mayThrow: Set<string>;
+  /** The functions that propagate exceptions by unwinding (unwind-abi.ts). */
+  readonly unwindAbi: Set<string>;
+  /** Whether the function being emitted is one of unwindAbi. */
+  currentUnwindAbi = false;
   readonly indirectMayThrow: boolean;
   /** Worker programs: the functions that poll for termination on entry
    * (workerTerminationPolls); null outside worker programs. */
@@ -1725,6 +1765,16 @@ export class LlEmitter {
       nodes: this.nodeIndex,
     });
     this.mayThrow = mt.fns;
+    this.unwindAbi =
+      options.unwindAbi === true &&
+      !this.wasi &&
+      mod.lib === undefined &&
+      options.debugSources === undefined &&
+      (options.targetTriple
+        ? /-linux-(?:gnu|musl)/.test(options.targetTriple)
+        : process.platform === "linux")
+        ? unwindAbiFunctions(mod, this.mayThrow, options.unwindExcluded)
+        : new Set();
     this.workerEntryPolls = mt.workerEntryPolls ?? null;
     this.stackChecks = mt.stackChecks ?? null;
     // A stackless call's eager prefix borrows its caller's stack; the
@@ -1860,6 +1910,9 @@ export class LlEmitter {
               : undefined,
           )
         : NO_INTEGER_CLONES;
+    // Integer clones and their dispatchers call each other through their
+    // own lowering, which keeps plain calls and flag tests.
+    for (const name of this.integerClones.members) this.unwindAbi.delete(name);
     this.stackCallbacks = new StackCallbacks(this.fnByName);
     this.receiverReaders = new AmbientReceiverReaders(this.fnByName, this.nodeIndex);
     this.stackCaptures = new StackCaptures(this.fnByName, this.callLifetimes, this.stackCallbacks);
@@ -2139,7 +2192,8 @@ export class LlEmitter {
     return this.emitParts().join("\n");
   }
   emitParts(): string[] {
-    return emitParts(this);
+    const parts = emitParts(this);
+    return this.unwindAbi.size > 0 ? bridgePlainUnwindCalls(parts) : parts;
   }
 
   /** The dispose-observer gates the emitted frees and record writers test
@@ -3249,6 +3303,13 @@ export class LlEmitter {
       terminator = `br label %${target.label}`;
     } else if (this.currentCoro !== null) {
       terminator = `br label %${this.currentCoro.finalLabel}`;
+    } else if (this.currentUnwindAbi && this.inLandingPad) {
+      // The unwind that entered the landing pad goes on to the caller's.
+      terminator = UNWIND_RESUME;
+    } else if (this.currentUnwindAbi) {
+      // The caller's invoke takes the exception at its landing pad.
+      this.declare(UNWIND_RAISE_DECLARATION);
+      terminator = UNWIND_RAISE;
     } else {
       const t = this.llType(this.currentReturnType);
       terminator =
@@ -3279,6 +3340,7 @@ export class LlEmitter {
         passThrough !== undefined &&
         !target &&
         this.currentCoro === null &&
+        !this.currentUnwindAbi &&
         !this.currentInt32Result
       ) {
         const t = this.llType(this.currentReturnType);
@@ -3465,6 +3527,46 @@ export class LlEmitter {
     B.startBlock(B.newLabel("exc.dead"));
   }
 
+  /** Emits `line`, a `call` of `callee`, and reports whether the call
+   * needs no pending check after it: a call of an unwinding-ABI function
+   * becomes an `invoke` whose landing pad runs this frame's unwind (the
+   * same releases and handler as emitPendingCheck's unwind path), and the
+   * normal path continues in a fresh block. Coroutine bodies keep plain
+   * calls (unwindAbiFunctions excludes their callees). */
+  emitDirectCall(line: string, callee: string): boolean {
+    const B = this.B;
+    if (!this.unwindAbi.has(callee) || this.currentCoro !== null || B.isTerminated()) {
+      B.line(line);
+      return false;
+    }
+    const ok = B.newLabel("inv.ok");
+    const pad = B.newLabel("inv.lp");
+    this.usesLandingPads = true;
+    // A trailing comment goes after the invoke's labels.
+    const comment = line.indexOf(" ; ");
+    const text = comment < 0 ? line : line.slice(0, comment);
+    B.terminate(
+      `${text.replace(/^((?:%[\w.]+ = )?)call /, "$1invoke ")} to label %${ok} unwind label %${pad}`,
+    );
+    B.startBlock(pad);
+    const exception = B.tmp();
+    B.line(`${exception} = landingpad { ptr, i32 } cleanup`);
+    if (this.currentUnwindAbi) B.line(`store { ptr, i32 } ${exception}, ptr ${UNWIND_SLOT}`);
+    this.inLandingPad = true;
+    this.emitUnwind();
+    this.inLandingPad = false;
+    B.startBlock(ok);
+    return true;
+  }
+
+  /** Whether emitUnwind runs for a landing pad, whose unwind goes on with
+   * `resume` instead of raising again. */
+  private inLandingPad = false;
+
+  /** Whether the function being emitted has a landing pad (its definition
+   * needs the personality). */
+  usesLandingPads = false;
+
   /** A recursive function's entry check: below the running stack's guard,
    * throw Node's RangeError and unwind like any other pending exception. */
   emitStackCheck(): void {
@@ -5238,7 +5340,22 @@ export class LlEmitter {
     if (fn.captures !== undefined) params.unshift("ptr %sc_env");
     const ret = this.llType(fn.returnType);
     const call = `call ${ret} @${mangleBorrowedFunction(fn.name)}(${params.join(", ")})`;
-    B.line(ret === "void" ? call : `%result = ${call}`);
+    // The owned entry of an unwinding-ABI body releases the borrowed
+    // parameters on the unwind too, then resumes it to its caller.
+    const unwinding = this.unwindAbi.has(fn.name) && kept.size === 0;
+    if (unwinding) {
+      const ok = B.newLabel("adapt.ok");
+      const pad = B.newLabel("adapt.lp");
+      B.terminate(
+        `${ret === "void" ? "" : "%result = "}invoke ${call.slice(5)} to label %${ok} unwind label %${pad}`,
+      );
+      B.startBlock(pad);
+      const exception = B.tmp();
+      B.line(`${exception} = landingpad { ptr, i32 } cleanup`);
+      for (const index of borrowed) this.releaseFrame(`%p${index}`, fn.params[index]!.type);
+      B.terminate(`resume { ptr, i32 } ${exception}`);
+      B.startBlock(ok);
+    } else B.line(ret === "void" ? call : `%result = ${call}`);
     // A borrowed result is reachable from the parameters: own it first. A
     // throwing body returns a null dummy, which needs no owner (and string
     // or array retains do not accept NULL).
@@ -5264,7 +5381,9 @@ export class LlEmitter {
     B.terminate(ret === "void" ? "ret void" : `ret ${ret} ${result}`);
     const symbol =
       kept.size > 0 ? `${mangleBorrowedFunction(fn.name)}.virtual` : mangleFunction(fn.name);
-    return `define internal ${ret} @${symbol}(${params.join(", ")}) ${FN_ATTRS} {\n${B.render()}\n}`;
+    if (unwinding) this.declare(`declare i32 @__gcc_personality_v0(...)`);
+    const personality = unwinding ? ` ${UNWIND_PERSONALITY}` : "";
+    return `define internal ${ret} @${symbol}(${params.join(", ")}) ${FN_ATTRS}${personality} {\n${B.render()}\n}`;
   }
   canBorrowCallArgument(value: IrExpr): boolean {
     return canBorrowCallArgument(this, value);
diff --git a/packages/compiler/src/backend/llvm/expr-calls.ts b/packages/compiler/src/backend/llvm/expr-calls.ts
index 6ff52619e..d411d9172 100644
--- a/packages/compiler/src/backend/llvm/expr-calls.ts
+++ b/packages/compiler/src/backend/llvm/expr-calls.ts
@@ -244,38 +244,46 @@ export function emitCallExpr(
         ? INTEGER_DISPATCH_SUFFIX
         : "";
       const target = `@${borrowed ? mangleBorrowedFunction(e.callee) : host.callTarget(e.callee)}${abi ? INT32_ABI_SUFFIX : ""}${dispatch}`;
+      // A call of an unwinding-ABI callee is an invoke (emitDirectCall):
+      // its landing pad unwinds, so no pending check follows it.
       if (e.type.kind === "void") {
-        B.line(`call void ${target}(${argList})`);
-        if (host.mayThrow.has(e.callee)) host.emitPendingCheck();
+        const invoked = host.emitDirectCall(`call void ${target}(${argList})`, e.callee);
+        if (!invoked && host.mayThrow.has(e.callee)) host.emitPendingCheck();
         if (borrowed) host.releaseTemps(host.frames.pop()!);
         return { name: "", type: e.type };
       }
       const t = B.tmp();
       if (abi?.union) {
-        B.line(`${t} = call ${SCALAR_UNION_RESULT} ${target}(${argList})`);
-        if (host.mayThrow.has(e.callee)) host.emitPendingCheck();
+        const invoked = host.emitDirectCall(
+          `${t} = call ${SCALAR_UNION_RESULT} ${target}(${argList})`,
+          e.callee,
+        );
+        if (!invoked && host.mayThrow.has(e.callee)) host.emitPendingCheck();
         if (borrowed) host.releaseTemps(host.frames.pop()!);
         if (stackResult) return host.stackScalarUnion(t, e.type);
         return host.own({ name: host.boxScalarUnion(t, e.type), type: e.type });
       }
       if (abi?.result) {
-        B.line(`${t} = call i32 ${target}(${argList})`);
+        const invoked = host.emitDirectCall(`${t} = call i32 ${target}(${argList})`, e.callee);
         const out = host.int32Result(t, e.type);
-        if (host.mayThrow.has(e.callee)) host.emitPendingCheck(out);
+        if (!invoked && host.mayThrow.has(e.callee)) host.emitPendingCheck(out);
         if (borrowed) host.releaseTemps(host.frames.pop()!);
         return out;
       }
-      B.line(`${t} = call ${host.llType(e.type)} ${target}(${argList})`);
+      const invoked = host.emitDirectCall(
+        `${t} = call ${host.llType(e.type)} ${target}(${argList})`,
+        e.callee,
+      );
       let out: LlValue;
       if (borrowed && host.borrowedReturns.has(e.callee)) {
         // A borrowed-return body hands back +0 (a null dummy when it threw):
         // test the exception first, then own the result before the
         // argument snapshots that keep it reachable are released.
-        if (host.mayThrow.has(e.callee)) host.emitPendingCheck();
+        if (!invoked && host.mayThrow.has(e.callee)) host.emitPendingCheck();
         out = host.own({ name: host.retainFrame(t, e.type), type: e.type });
       } else {
         out = host.own({ name: t, type: e.type });
-        if (host.mayThrow.has(e.callee)) host.emitPendingCheck(out);
+        if (!invoked && host.mayThrow.has(e.callee)) host.emitPendingCheck(out);
       }
       if (borrowed) {
         host.toFrame(out);
@@ -1366,10 +1374,11 @@ export function emitBorrowedResultCall(host: LlvmEmitterContext, e: ExprOf<"call
     )
     .join(", ");
   const t = host.B.tmp();
-  host.B.line(
+  const invoked = host.emitDirectCall(
     `${t} = call ${host.llType(e.type)} @${mangleBorrowedFunction(e.callee)}${abi ? INT32_ABI_SUFFIX : ""}(${argList}) ; borrowed result`,
+    e.callee,
   );
-  if (host.mayThrow.has(e.callee)) host.emitPendingCheck();
+  if (!invoked && host.mayThrow.has(e.callee)) host.emitPendingCheck();
   return { name: t, type: e.type };
 }
 
diff --git a/packages/compiler/src/backend/llvm/unwind-abi.test.ts b/packages/compiler/src/backend/llvm/unwind-abi.test.ts
new file mode 100644
index 000000000..5f7f5895b
--- /dev/null
+++ b/packages/compiler/src/backend/llvm/unwind-abi.test.ts
@@ -0,0 +1,285 @@
+import { mkdtemp, readFile, rm, writeFile } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { expect, test } from "vitest";
+import { compile, deserializeModule } from "../../index.js";
+import { validateModule } from "../../ir/validate.js";
+import { emitLlvmModule } from "./emitter.js";
+import { UnwindAbiViolation, bridgePlainUnwindCalls } from "./unwind-abi.js";
+
+async function moduleFor(source: string) {
+  const dir = await mkdtemp(join(tmpdir(), "scriptc-unwind-abi-"));
+  try {
+    const entry = join(dir, "main.ts"),
+      output = join(dir, "main.ir.json");
+    await writeFile(entry, source);
+    const result = await compile(entry, { outDir: dir, outPath: output, outputKind: "ir" });
+    if (!result.ok)
+      throw new Error(result.diagnostics.map((item) => `${item.code}: ${item.message}`).join("\n"));
+    const module = deserializeModule(await readFile(output, "utf8"));
+    expect(validateModule(module)).toEqual([]);
+    return module;
+  } finally {
+    await rm(dir, { recursive: true, force: true });
+  }
+}
+
+/** The definition of the source function `name` (its i32 or borrowing entry when it has one). */
+function body(ir: string, name: string): string {
+  return new RegExp(
+    `^define internal [^\\n]*@sc_b?f_[^\\n(]*${name}(?:\\.i32)?\\([^]*?^}`,
+    "m",
+  ).exec(ir)![0];
+}
+
+const SOURCE = `
+function leaf(n: number): number {
+  if (n === 3) throw new RangeError("three");
+  return n * 2;
+}
+function first(n: number): number {
+  return leaf(n) + 1;
+}
+function second(n: number): number {
+  return first(n) * 3;
+}
+function third(n: number): number {
+  return second(n) - 2;
+}
+function mid(n: number): number {
+  const parts: string[] = ["a" + n];
+  const r = third(n);
+  parts.push("b");
+  return r + parts.length;
+}
+class Counter {
+  total = 0;
+  add(n: number): void { this.total += mid(n); }
+}
+function outer(n: number): string {
+  try { return "ok " + mid(n); } catch (e) { return "caught " + (e as Error).message; }
+}
+const counter = new Counter();
+for (let i = 0; i < 5; i++) { console.log(outer(i)); try { counter.add(i); } catch { console.log("add", i); } }
+const f = (x: number) => mid(x);
+console.log(f(1), counter.total);
+`;
+
+const LINUX = { targetTriple: "x86_64-unknown-linux-gnu", unwindAbi: true } as const;
+
+test("directly called functions raise, and their callers invoke them without a pending check", async () => {
+  const ir = emitLlvmModule(await moduleFor(SOURCE), LINUX);
+  // leaf throws: the exception starts on the pending flag, and the three
+  // calls above it test the flag too; mid raises it on.
+  for (const name of ["leaf", "first", "second", "third"])
+    expect(body(ir, name)).not.toContain("@scr_unwind_raise");
+  const mid = body(ir, "mid");
+  expect(mid).toMatch(/= call double @sc_b?f_[^(]*third\(/);
+  expect(mid).toContain("call void @scr_unwind_raise()");
+  // outer invokes mid; the landing pad takes the exception to its handler.
+  const outer = body(ir, "outer");
+  expect(outer).toMatch(
+    /= invoke double @sc_b?f_[^(]*mid[^\n]* to label %inv\.ok\d+ unwind label %inv\.lp\d+/,
+  );
+  expect(outer).toMatch(/inv\.lp\d+:\n\s+%t\d+ = landingpad \{ ptr, i32 \} cleanup/);
+  expect(outer).toContain("personality ptr @__gcc_personality_v0");
+  expect(ir).toContain("declare i32 @__gcc_personality_v0(...)");
+  expect(ir).toContain("declare void @scr_unwind_raise() cold");
+});
+
+test("a method of a class outside any hierarchy is on the unwinding ABI; closures keep the flag", async () => {
+  const ir = emitLlvmModule(await moduleFor(SOURCE), LINUX);
+  // Counter.add invokes mid and resumes the unwind from its landing pad; the
+  // closure over mid is a pointer target and returns with the flag.
+  const add = body(ir, "Counter_add");
+  expect(add).toMatch(/invoke double @sc_b?f_[^(]*mid/);
+  expect(add).toMatch(/resume \{ ptr, i32 \} %[\w.]+/);
+  expect(add).not.toContain("@scr_unwind_raise");
+  const closures = ir
+    .split(/\n(?=define )/)
+    .filter((def) => /^define internal [^\n]*@sc_b?f_[^\n(]*fn_/.test(def));
+  expect(closures.length).toBeGreaterThan(0);
+  for (const def of closures) expect(def).not.toContain("call void @scr_unwind_raise()");
+});
+
+test("recursive functions keep the pending flag, also when they recurse through a callback", async () => {
+  const source = `
+function leaf(n: number): number {
+  if (n < 0) throw new RangeError("negative");
+  return n;
+}
+function one(n: number): number { return leaf(n) + 1; }
+function two(n: number): number { return one(n) + 1; }
+function three(n: number): number { return two(n) + 1; }
+function four(n: number): number {
+  const parts: string[] = ["a" + n];
+  const r = three(n);
+  return r + parts.length;
+}
+function walk(n: number, depth: number): number {
+  const parts: string[] = ["w" + n];
+  const r = depth === 0 ? four(n) : walk(n, depth - 1);
+  return r + parts.length;
+}
+function visit(n: number, depth: number, each: (n: number, depth: number) => number): number {
+  const parts: string[] = ["v" + n];
+  const r = depth === 0 ? four(n) : each(n, depth - 1);
+  return r + parts.length;
+}
+const each = (n: number, depth: number): number => visit(n, depth, each);
+for (let i = -1; i < 2; i++) {
+  try { console.log(walk(i, 3), visit(i, 3, each)); } catch (e) { console.log((e as Error).message); }
+}
+`;
+  const ir = emitLlvmModule(await moduleFor(source), LINUX);
+  expect(body(ir, "four")).toContain("call void @scr_unwind_raise()");
+  for (const name of ["walk", "visit"]) {
+    expect(body(ir, name)).not.toContain("@scr_unwind_raise");
+    expect(body(ir, name)).toMatch(/invoke double @sc_b?f_[^(]*four/);
+  }
+});
+
+test("without the option, and off Linux, emission keeps the pending-flag ABI", async () => {
+  const mod = await moduleFor(SOURCE);
+  for (const options of [{}, { targetTriple: "arm64-apple-macosx14.0.0", unwindAbi: true }]) {
+    const ir = emitLlvmModule(mod, options);
+    expect(ir).not.toContain("invoke ");
+    expect(ir).not.toContain("@scr_unwind_raise");
+    expect(ir).not.toContain("personality");
+  }
+});
+
+test("bridgePlainUnwindCalls keeps the pending-flag contract at plain calls of raising functions", () => {
+  const raising = [
+    "define internal ptr @sc_bf_raises(ptr %p) #0 { ; raises",
+    "entry:",
+    "  call void @scr_unwind_raise()",
+    "  unreachable",
+    "}",
+  ].join("\n");
+  const caller = [
+    "define internal ptr @sc_f_adapter(ptr %p0) #0 {",
+    "entry:",
+    "  %result = call ptr @sc_bf_raises(ptr %p0) ; borrowed result",
+    "  br label %next",
+    "next:",
+    "  %v = phi ptr [ %result, %entry ]",
+    "  ret ptr %v",
+    "}",
+  ].join("\n");
+  const [out] = bridgePlainUnwindCalls([`${raising}\n${caller}`]);
+  expect(out).toContain(
+    "%result.ub = invoke ptr @sc_bf_raises(ptr %p0) to label %ub.n.0 unwind label %ub.lp.0",
+  );
+  expect(out).toContain("%result = phi ptr [ %result.ub, %ub.n.0 ], [ null, %ub.lp.0 ]");
+  // The split block's successor now comes from its last part.
+  expect(out).toContain("%v = phi ptr [ %result, %ub.ok.0 ]");
+  expect(out).toMatch(
+    /define internal ptr @sc_f_adapter\(ptr %p0\) #0 personality ptr @__gcc_personality_v0 \{/,
+  );
+  expect(out).toContain("declare i32 @__gcc_personality_v0(...)");
+});
+
+test("an invoked wrapper of a raising function resumes the unwind; its address must not escape", () => {
+  const raising = [
+    "define internal double @sc_bf_body.i32(i32 %a) #0 {",
+    "entry:",
+    "  call void @scr_unwind_raise()",
+    "  unreachable",
+    "}",
+  ].join("\n");
+  const wrapper = [
+    "define internal double @sc_bf_body(double %a) #0 {",
+    "entry:",
+    "  %i = fptosi double %a to i32",
+    "  %r = call double @sc_bf_body.i32(i32 %i)",
+    "  ret double %r",
+    "}",
+  ].join("\n");
+  const caller = [
+    "define internal double @sc_bf_caller(double %a) #0 personality ptr @__gcc_personality_v0 {",
+    "entry:",
+    "  %r = invoke double @sc_bf_body(double %a) to label %ok unwind label %lp",
+    "lp:",
+    "  %x = landingpad { ptr, i32 } cleanup",
+    "  call void @scr_unwind_raise()",
+    "  unreachable",
+    "ok:",
+    "  ret double %r",
+    "}",
+  ].join("\n");
+  const [out] = bridgePlainUnwindCalls([[raising, wrapper, caller].join("\n")]);
+  expect(out).toContain(
+    "%r = invoke double @sc_bf_body.i32(i32 %i) to label %ub.ok.0 unwind label %ub.lp.0",
+  );
+  expect(out).toContain("resume { ptr, i32 } %ub.v.0");
+  expect(() =>
+    bridgePlainUnwindCalls([
+      `${raising}\n@table = internal constant [1 x ptr] [ptr @sc_bf_body.i32]`,
+    ]),
+  ).toThrow(UnwindAbiViolation);
+  try {
+    bridgePlainUnwindCalls([
+      `${raising}\n@table = internal constant [1 x ptr] [ptr @sc_bf_body.i32]`,
+    ]);
+  } catch (error) {
+    expect([...(error as UnwindAbiViolation).symbols]).toEqual(["sc_bf_body.i32"]);
+  }
+});
+
+test("an invoked function that never tests the pending flag needs no raise", () => {
+  const raising = [
+    "define internal void @sc_bf_raises() #0 {",
+    "entry:",
+    "  call void @scr_unwind_raise()",
+    "  unreachable",
+    "}",
+  ].join("\n");
+  const leaf = [
+    "define internal double @sc_bf_leaf() #0 {",
+    "entry:",
+    "  ret double 1.0",
+    "}",
+  ].join("\n");
+  const caller = (callee: string) =>
+    [
+      "define internal double @sc_bf_caller() #0 personality ptr @__gcc_personality_v0 {",
+      "entry:",
+      `  %r = invoke double @${callee}() to label %ok unwind label %lp`,
+      "lp:",
+      "  %x = landingpad { ptr, i32 } cleanup",
+      "  call void @scr_unwind_raise()",
+      "  unreachable",
+      "ok:",
+      "  ret double %r",
+      "}",
+    ].join("\n");
+  expect(() =>
+    bridgePlainUnwindCalls([[raising, leaf, caller("sc_bf_leaf")].join("\n")]),
+  ).not.toThrow();
+  const testing = leaf.replace(
+    "  ret double 1.0",
+    "  %f = load i32, ptr @scr_exc_flag\n  ret double 1.0",
+  );
+  expect(() =>
+    bridgePlainUnwindCalls([[raising, testing, caller("sc_bf_leaf")].join("\n")]),
+  ).toThrow(UnwindAbiViolation);
+});
+
+test("calls that cannot unwind are marked nounwind", () => {
+  const raising = [
+    "define internal void @sc_bf_raises(ptr %b) #0 {",
+    "entry:",
+    "  %n = call i64 @scr_bytes_length(ptr %b) ; length",
+    "  call void @scr_bytes_release(ptr %b), !dbg !4",
+    "  %r = call ptr %b(ptr %b)",
+    "  call void @scr_unwind_raise()",
+    "  unreachable",
+    "}",
+  ].join("\n");
+  const [out] = bridgePlainUnwindCalls([raising]);
+  expect(out).toContain("%n = call i64 @scr_bytes_length(ptr %b) nounwind ; length");
+  expect(out).toContain("call void @scr_bytes_release(ptr %b) nounwind, !dbg !4");
+  expect(out).toContain("%r = call ptr %b(ptr %b) nounwind");
+  expect(out).toContain("  call void @scr_unwind_raise()\n");
+});
diff --git a/packages/compiler/src/backend/llvm/unwind-abi.ts b/packages/compiler/src/backend/llvm/unwind-abi.ts
new file mode 100644
index 000000000..4dc611913
--- /dev/null
+++ b/packages/compiler/src/backend/llvm/unwind-abi.ts
@@ -0,0 +1,491 @@
+/* The functions that propagate exceptions by unwinding instead of the
+ * pending flag (see unwindAbiFunctions). */
+import type { IrExpr, IrModule } from "../../ir/ir.js";
+import { everyStmtList } from "../../ir/traverse.js";
+
+/** How many calls above a `throw` functions keep the pending flag. */
+const THROW_LEVELS = 3;
+/** The call graph's node for calls through values. */
+const ANY_FUNCTION = " any function";
+
+/** The nodes of `edges` on a cycle (a recursion), by Tarjan's algorithm
+ * without recursion of its own: a large module's call chains are deeper
+ * than the host stack. */
+function recursiveFunctions(edges: ReadonlyMap<string, readonly string[]>): Set<string> {
+  const index = new Map<string, number>();
+  const low = new Map<string, number>();
+  const stack: string[] = [];
+  const onStack = new Set<string>();
+  const result = new Set<string>();
+  let counter = 0;
+  const enter = (name: string): { name: string; next: number } => {
+    index.set(name, counter);
+    low.set(name, counter++);
+    stack.push(name);
+    onStack.add(name);
+    return { name, next: 0 };
+  };
+  for (const root of edges.keys()) {
+    if (index.has(root)) continue;
+    const work = [enter(root)];
+    while (work.length > 0) {
+      const top = work[work.length - 1]!;
+      const out = edges.get(top.name) ?? [];
+      if (top.next < out.length) {
+        const callee = out[top.next++]!;
+        if (!index.has(callee)) work.push(enter(callee));
+        else if (onStack.has(callee))
+          low.set(top.name, Math.min(low.get(top.name)!, index.get(callee)!));
+        continue;
+      }
+      work.pop();
+      const parent = work[work.length - 1];
+      if (parent !== undefined)
+        low.set(parent.name, Math.min(low.get(parent.name)!, low.get(top.name)!));
+      if (low.get(top.name) !== index.get(top.name)) continue;
+      const members: string[] = [];
+      let member: string;
+      do {
+        member = stack.pop()!;
+        onStack.delete(member);
+        members.push(member);
+      } while (member !== top.name);
+      if (members.length > 1 || out.includes(top.name)) for (const m of members) result.add(m);
+    }
+  }
+  return result;
+}
+
+/** The may-throw functions whose exceptions reach their callers by
+ * unwinding the native stack (scr_unwind_raise) instead of returning with
+ * the pending flag set. Their callers call them with `invoke`, so the call
+ * needs no flag test; the landing pad runs the frame's unwind.
+ *
+ * A function qualifies only when every way it can be reached is a direct
+ * `call` from emitted code that can lower it as an `invoke`: it is not
+ * async or a generator, not a constructor, not a method a virtual call can
+ * reach or one a vtable holds (an overridden method), not a closure
+ * target, not the entry or a library export, not named by any node other
+ * than a `call`'s callee, and not called from an async or generator body
+ * (coroutine bodies keep plain calls).
+ *
+ * A native unwind costs about 2 µs a raise and 0.1 µs a frame, against a
+ * few nanoseconds for a flag test, so the functions an exception is likely to
+ * cross many of keep the flag: those with a `throw` or rethrow of their own
+ * and those up to THROW_LEVELS calls above one (a handler near the throw
+ * takes it without a native unwind), and the recursive ones (deep stacks
+ * are recursions). */
+export function unwindAbiFunctions(
+  mod: IrModule,
+  mayThrow: ReadonlySet<string>,
+  excluded: ReadonlySet<string> = new Set(),
+): Set<string> {
+  const names = new Set(mod.functions.map((fn) => fn.name));
+  const blocked = new Set<string>(excluded);
+  blocked.add(mod.entry);
+  // The runtime calls the error property readers through the pointers the
+  // module installs (emit-module.ts).
+  blocked.add("%error.name.read");
+  blocked.add("%error.message.read");
+  for (const entry of mod.lib?.exports ?? []) blocked.add(entry.fnName);
+  // Methods a virtual call can reach, and the overridden methods of class
+  // hierarchies (whose vtables list them), are called through pointers; the
+  // others are called directly, like functions. A virtual call reaches its listed
+  // targets, or else the method in its receiver class's hierarchy; a
+  // receiver that is no class of the module (an interface) may reach any
+  // class's method of that name.
+  const classes = new Map((mod.classes ?? []).map((cls) => [cls.name, cls]));
+  const anyClass = new Set<string>();
+  for (const fn of mod.functions)
+    everyStmtList(fn.body, {
+      expr: (e: IrExpr) => {
+        if (e.kind !== "virtualCall") return true;
+        if (e.targets !== undefined) for (const target of e.targets) blocked.add(target);
+        else if (classes.has(e.className)) blocked.add(`%${e.className}.${e.method}`);
+        else anyClass.add(e.method);
+        return true;
+      },
+      stmt: () => true,
+    });
+  // A hierarchy's vtables hold the methods declared by more than one of its
+  // classes (an override and what it overrides).
+  const rootOf = (name: string): string => {
+    let cls = classes.get(name);
+    while (cls?.base !== undefined && classes.has(cls.base)) cls = classes.get(cls.base);
+    return cls?.name ?? name;
+  };
+  const declarers = new Map<string, number>();
+  for (const cls of mod.classes ?? [])
+    for (const m of cls.methods ?? []) {
+      const key = `${rootOf(cls.name)}\0${m}`;
+      declarers.set(key, (declarers.get(key) ?? 0) + 1);
+    }
+  for (const cls of mod.classes ?? []) {
+    blocked.add(`%${cls.name}.constructor`);
+    blocked.add(`%${cls.name}.construct`);
+    const root = rootOf(cls.name);
+    for (const m of cls.methods ?? [])
+      if (anyClass.has(m) || declarers.get(`${root}\0${m}`)! > 1) blocked.add(`%${cls.name}.${m}`);
+  }
+  // Any function a node names other than as a call's callee may be reached
+  // through a pointer.
+  const referenced = new Set<string>();
+  const noteNames = (node: object, skip: string | undefined): void => {
+    for (const key in node) {
+      if (key === skip) continue;
+      const value = (node as Record<string, unknown>)[key];
+      if (typeof value === "string" && names.has(value)) referenced.add(value);
+    }
+  };
+  // The call graph, for the functions near a throw and the recursive ones.
+  // Calls through values (closures, class values, dynamic calls, callbacks
+  // passed to the runtime) reach ANY_FUNCTION, which reaches every function
+  // a value can hold.
+  const throws = new Set<string>();
+  const callers = new Map<string, string[]>();
+  const callees = new Map<string, string[]>();
+  const edge = (from: string, to: string): void => {
+    let list = callers.get(to);
+    if (list === undefined) callers.set(to, (list = []));
+    list.push(from);
+    let out = callees.get(from);
+    if (out === undefined) callees.set(from, (out = []));
+    out.push(to);
+  };
+  const methodsNamed = new Map<string, string[]>();
+  for (const cls of mod.classes ?? [])
+    for (const m of cls.methods ?? []) {
+      let list = methodsNamed.get(m);
+      if (list === undefined) methodsNamed.set(m, (list = []));
+      list.push(`%${cls.name}.${m}`);
+    }
+  for (const fn of mod.functions) {
+    const coroutine = fn.async === true || fn.generator !== undefined;
+    everyStmtList(fn.body, {
+      expr: (e: IrExpr) => {
+        const kind = e.kind as string;
+        if (kind === "throw" || kind === "rethrow") throws.add(fn.name);
+        if (e.kind === "call") {
+          edge(fn.name, e.callee);
+          // The entry's callees (the module initializers) run once: on the
+          // flag they keep landing pads out of the top-level code inlined
+          // into the entry.
+          if (coroutine || fn.name === mod.entry) blocked.add(e.callee);
+          noteNames(e, "callee");
+          return true;
+        }
+        noteNames(e, undefined);
+        if (e.kind === "virtualCall")
+          for (const target of e.targets ?? methodsNamed.get(e.method) ?? []) edge(fn.name, target);
+        else if (e.kind === "new") {
+          edge(fn.name, `%${e.className}.constructor`);
+          edge(fn.name, `%${e.className}.construct`);
+        } else if (kind === "callValue" || kind === "dynCall" || kind === "newValue")
+          edge(fn.name, ANY_FUNCTION);
+        else if ("args" in e) {
+          const args: unknown = e.args;
+          if (Array.isArray(args))
+            for (const arg of args as IrExpr[])
+              if (arg.type.kind === "func") edge(fn.name, ANY_FUNCTION);
+        }
+        return true;
+      },
+      stmt: (s) => {
+        const kind = s.kind as string;
+        if (kind === "throw" || kind === "rethrow") throws.add(fn.name);
+        noteNames(s, undefined);
+        return true;
+      },
+    });
+  }
+  for (const name of referenced) {
+    blocked.add(name);
+    edge(ANY_FUNCTION, name);
+  }
+  // A throw starts on the pending flag, and so do the functions up to
+  // THROW_LEVELS calls above it. The union narrowing helpers' throws (a
+  // failed narrowing) don't count for their callers.
+  for (const name of throws) blocked.add(name);
+  let level = [...throws].filter((name) => !name.startsWith("%union."));
+  const near = new Set(level);
+  for (let i = 0; i < THROW_LEVELS; i++) {
+    const next: string[] = [];
+    for (const name of level)
+      for (const caller of callers.get(name) ?? [])
+        if (!near.has(caller)) {
+          near.add(caller);
+          next.push(caller);
+        }
+    level = next;
+  }
+  for (const name of near) blocked.add(name);
+  for (const name of recursiveFunctions(callees)) blocked.add(name);
+  const result = new Set<string>();
+  for (const fn of mod.functions) {
+    if (!mayThrow.has(fn.name) || blocked.has(fn.name)) continue;
+    if (fn.async === true || fn.generator !== undefined) continue;
+    result.add(fn.name);
+  }
+  return result;
+}
+
+/** What an unwinding-ABI function's unwind ends with when no handler of
+ * its own takes the exception. */
+export const UNWIND_RAISE = "call void @scr_unwind_raise()\n  unreachable";
+/** What the unwind of a landing pad ends with when no handler of the
+ * function takes the exception: the unwind goes on (`resume`) with the
+ * exception the landing pad stored in UNWIND_SLOT. The block builder
+ * expands it (BlockBuilder.terminate). */
+export const UNWIND_RESUME = "resume { ptr, i32 } <unwind slot>";
+/** The function's slot for the exception its landing pads take. */
+export const UNWIND_SLOT = "%unw.exc";
+/** scr_unwind_raise's declaration. It is not `noreturn`: sanitized builds
+ * would call the sanitizer's no-return hook before it, which fails on fiber
+ * stacks; scr_unwind_raise clears the unwound frames' shadow itself. */
+export const UNWIND_RAISE_DECLARATION = "declare void @scr_unwind_raise() cold";
+
+/** The personality of functions with landing pads: the landing pads are
+ * cleanups that scr_unwind_raise's forced unwind runs. */
+export const UNWIND_PERSONALITY = "personality ptr @__gcc_personality_v0";
+
+/** An unwind leaving the function: a raise, or a landing pad's `resume`. */
+const UNWINDS = /call void @scr_unwind_raise\(\)|\n\s+resume /;
+/** A pending-flag test: the thread's exception word, the active cell, or the runtime query. */
+const PENDING_TEST = /@scr_exc_flag\b|%exc\.cell\b|@scr_exc_active\b|@scr_exc_pending\(/;
+
+/** Functions emission found breaking the unwinding ABI's rules
+ * (bridgePlainUnwindCalls), by symbol: the caller emits the module again
+ * with them on the pending-flag ABI. */
+export class UnwindAbiViolation extends Error {
+  readonly symbols: ReadonlySet<string>;
+  constructor(symbols: ReadonlySet<string>) {
+    super(`unwinding ABI: ${[...symbols].slice(0, 3).join(", ")} must keep the pending flag`);
+    this.symbols = symbols;
+  }
+}
+const DEFINE_NAME = /^define [^@\n]*@([\w.$%-]+)\(/;
+const PLAIN_CALL = /^(\s*)(%[\w.$-]+) = call (.*?)@([\w.$%-]+)\(|^(\s*)call (.*?)@([\w.$%-]+)\(/;
+const RETURN_ATTRIBUTES =
+  /\b(?:zeroext|signext|noalias|nonnull|noundef|inreg|dereferenceable(?:_or_null)?\(\d+\)|align \d+)\s+/g;
+
+/** A call instruction's line. */
+const CALL_LINE = /^\s*(?:%[\w.$-]+ = )?(?:(?:tail|musttail|notail) )?call /;
+/** A call's callee (a function or a register) and the parenthesis that
+ * opens its arguments. */
+const CALLEE = /[@%][\w.$%-]+\(/;
+
+/** The index of the parenthesis that closes the argument list opened at `open`. */
+function argumentsEnd(line: string, open: number): number {
+  let depth = 0;
+  let close = open;
+  for (; close < line.length; close++) {
+    const c = line.charAt(close);
+    if (c === "(") depth++;
+    else if (c === ")" && --depth === 0) break;
+  }
+  return close;
+}
+
+/** A call that cannot unwind, marked so: only scr_unwind_raise and the
+ * raising functions propagate an unwind (runtime code and every function
+ * reached through a pointer return normally), so every other call is
+ * `nounwind`, and the inliner keeps it a call where it inlines a raising
+ * function at an invoke. */
+function markNounwind(line: string): string {
+  const call = line.indexOf("call ");
+  const callee = CALLEE.exec(line.slice(call));
+  if (callee === null || callee[0] === "@scr_unwind_raise(") return line;
+  const close = argumentsEnd(line, call + callee.index + callee[0].length - 1);
+  return close >= line.length
+    ? line
+    : `${line.slice(0, close + 1)} nounwind${line.slice(close + 1)}`;
+}
+
+/** The value a bridged call yields on its landing pad: the dummy a
+ * pending-flag callee returns with an exception pending. */
+function dummyValue(type: string): string {
+  if (type === "ptr") return "null";
+  if (type === "double" || type === "float") return "0.0";
+  if (/^i\d+$/.test(type)) return "0";
+  return "zeroinitializer";
+}
+
+/** Rewrites every remaining plain call of an unwinding-ABI function (one
+ * that raises, scr_unwind_raise, or resumes an unwind) in `parts`, the module's text, into an
+ * invoke whose landing pad continues after the call with the exception
+ * pending and the call's dummy result: the pending-flag contract those
+ * call sites were emitted for, whichever lowering emitted them. Calls of
+ * these functions that emitDirectCall lowered are invokes already. */
+export function bridgePlainUnwindCalls(parts: string[]): string[] {
+  const raisers = new Set<string>();
+  const split = parts.map((part) => part.split(/\n(?=define )/));
+  for (const chunks of split)
+    for (const chunk of chunks) {
+      const m = DEFINE_NAME.exec(chunk);
+      if (m !== null && UNWINDS.test(chunk)) raisers.add(m[1]!);
+    }
+  if (raisers.size === 0) return parts;
+  // An invoke's callee must raise or never test the pending flag: one that
+  // returned with the flag pending would pass the exception by its invoking
+  // caller unseen. A wrapper an invoke reaches (an int32 or borrowed-ABI
+  // entry forwarding to the body) propagates its callee's unwind instead
+  // (`resume`), so it raises too. A raising function must be reached only by
+  // calls: a pointer to it (a vtable or table entry, a runtime callback)
+  // could be called without a landing pad. Functions that break either rule
+  // go back to the pending-flag ABI (UnwindAbiViolation).
+  const violations = new Set<string>();
+  const invoked = new Set<string>();
+  const testsFlag = new Set<string>();
+  for (const chunks of split)
+    for (const chunk of chunks) {
+      const m = DEFINE_NAME.exec(chunk);
+      if (m !== null && PENDING_TEST.test(chunk)) testsFlag.add(m[1]!);
+      for (const c of chunk.matchAll(/ invoke [^@\n]*@([\w.$%-]+)\(/g)) invoked.add(c[1]!);
+    }
+  const resumers = new Set<string>();
+  for (let grew = true; grew;) {
+    grew = false;
+    for (const chunks of split)
+      for (const chunk of chunks) {
+        const m = DEFINE_NAME.exec(chunk);
+        const name = m?.[1];
+        if (name === undefined || raisers.has(name) || !invoked.has(name)) continue;
+        if (![...chunk.matchAll(/ call [^@\n]*@([\w.$%-]+)\(/g)].some((c) => raisers.has(c[1]!)))
+          continue;
+        if (testsFlag.has(name)) continue;
+        raisers.add(name);
+        resumers.add(name);
+        grew = true;
+      }
+  }
+  for (const name of invoked) if (!raisers.has(name) && testsFlag.has(name)) violations.add(name);
+  for (const chunks of split)
+    for (const chunk of chunks)
+      for (const line of chunk.split("\n")) {
+        if (line.startsWith("define ")) continue;
+        for (const m of line.matchAll(/@([\w.$%-]+)/g)) {
+          if (!raisers.has(m[1]!)) continue;
+          const at = m.index!;
+          if (
+            /(?:call|invoke) [^@]*$/.test(line.slice(0, at)) &&
+            line.charAt(at + m[0].length) === "("
+          )
+            continue;
+          violations.add(m[1]!);
+        }
+      }
+  if (violations.size > 0) throw new UnwindAbiViolation(violations);
+  let personality = false;
+  let counter = 0;
+  const out = split.map((chunks) =>
+    chunks
+      .map((chunk) => {
+        if (!DEFINE_NAME.test(chunk) || !chunk.includes("call ")) return chunk;
+        const lines = chunk.split("\n");
+        const resume = resumers.has(DEFINE_NAME.exec(chunk)![1]!);
+        const result: string[] = [];
+        // The label a block's terminator now follows, for phi operands.
+        const moved = new Map<string, string>();
+        let block = "";
+        let changed = false;
+        for (let i = 0; i < lines.length; i++) {
+          const line = lines[i]!;
+          const label = /^([\w.$-]+):/.exec(line);
+          if (label !== null) block = label[1]!;
+          const m = PLAIN_CALL.exec(line);
+          const callee = m === null ? undefined : (m[4] ?? m[7]);
+          if (m === null || callee === undefined || !raisers.has(callee)) {
+            const marked = CALL_LINE.test(line) ? markNounwind(line) : line;
+            changed ||= marked !== line;
+            result.push(marked);
+            continue;
+          }
+          // The call's text from its callee to the end of the argument list.
+          const close = argumentsEnd(line, line.indexOf(`@${callee}(`) + callee.length + 1);
+          const head = line.slice(line.indexOf("call ") + 5, close + 1);
+          const tail = line.slice(close + 1);
+          const meta = /,\s*!/.exec(tail);
+          const attrs = (
+            meta === null ? tail.replace(/;.*$/, "") : tail.slice(0, meta.index)
+          ).trimEnd();
+          const dbg = meta === null ? "" : tail.slice(meta.index).replace(/\s;.*$/, "");
+          const n = counter++;
+          if (block === "") {
+            result.splice(1, 0, "entry.ub:");
+            block = "entry.ub";
+          }
+          const indent = m[1] ?? m[5] ?? "  ";
+          const ok = `ub.ok.${n}`;
+          const pad = `ub.lp.${n}`;
+          if (resume) {
+            // The wrapper holds nothing to release: the unwind goes on to
+            // its caller's landing pad.
+            const assign = m[2] !== undefined ? `${m[2]} = ` : "";
+            result.push(
+              `${indent}${assign}invoke ${head}${attrs} to label %${ok} unwind label %${pad}${dbg}`,
+            );
+            result.push(
+              `${pad}:`,
+              `${indent}%ub.v.${n} = landingpad { ptr, i32 } cleanup`,
+              `${indent}resume { ptr, i32 } %ub.v.${n}`,
+            );
+            result.push(`${ok}:`);
+          } else if (m[2] !== undefined) {
+            const type = (m[3] ?? "").replace(RETURN_ATTRIBUTES, "").trim();
+            const normal = `ub.n.${n}`;
+            result.push(
+              `${indent}${m[2]}.ub = invoke ${head}${attrs} to label %${normal} unwind label %${pad}${dbg}`,
+            );
+            result.push(`${normal}:`, `${indent}br label %${ok}`);
+            result.push(
+              `${pad}:`,
+              `${indent}%ub.v.${n} = landingpad { ptr, i32 } cleanup`,
+              `${indent}br label %${ok}`,
+            );
+            result.push(
+              `${ok}:`,
+              `${indent}${m[2]} = phi ${type} [ ${m[2]}.ub, %${normal} ], [ ${dummyValue(type)}, %${pad} ]`,
+            );
+          } else {
+            result.push(
+              `${indent}invoke ${head}${attrs} to label %${ok} unwind label %${pad}${dbg}`,
+            );
+            result.push(
+              `${pad}:`,
+              `${indent}%ub.v.${n} = landingpad { ptr, i32 } cleanup`,
+              `${indent}br label %${ok}`,
+            );
+            result.push(`${ok}:`);
+          }
+          moved.set(block, ok);
+          changed = true;
+        }
+        if (!changed) return chunk;
+        if (moved.size === 0) return result.join("\n");
+        personality = true;
+        const header = result[0]!;
+        const brace = header.lastIndexOf(" {");
+        if (!header.includes("personality") && brace >= 0) {
+          // Before the function's metadata attachments (`!dbg`), if any.
+          const dbg = header.slice(0, brace).search(/\s!dbg !\d+$/);
+          const at = dbg >= 0 ? dbg : brace;
+          result[0] = `${header.slice(0, at)} ${UNWIND_PERSONALITY}${header.slice(at)}`;
+        }
+        // A split block's successors now come from its last part.
+        if (moved.size > 0)
+          for (let i = 0; i < result.length; i++) {
+            const line = result[i]!;
+            if (!line.includes(" phi ")) continue;
+            result[i] = line.replace(/, %([\w.$-]+) \]/g, (all, name: string) => {
+              const to = moved.get(name);
+              return to === undefined ? all : `, %${to} ]`;
+            });
+          }
+        return result.join("\n");
+      })
+      .join("\n"),
+  );
+  if (personality && !out.some((part) => part.includes("@__gcc_personality_v0(...)")))
+    out[0] = `declare i32 @__gcc_personality_v0(...)\n${out[0]}`;
+  return out;
+}
diff --git a/packages/compiler/src/backend/native/executable.ts b/packages/compiler/src/backend/native/executable.ts
index ceb162bcc..1364bca4d 100644
--- a/packages/compiler/src/backend/native/executable.ts
+++ b/packages/compiler/src/backend/native/executable.ts
@@ -43,6 +43,7 @@ import {
   cacheTargetIdentity,
   isZigDriver,
   isMuslTarget,
+  type CcDriver,
 } from "./driver.js";
 import {
   resolveProgramShardMergeIdentity,
@@ -821,6 +822,7 @@ export async function compileCInternal(
     // generated/native input that references inflate symbols. Cross
     // and targetless Zig builds use vendored zlib objects in the input section above.
     ...(((opts.zlib ?? false) || nativeFetch) && !isZigDriver(driver) ? ["-lz"] : []),
+    ...unwinderLinkArgs(driver),
     // glibc keeps libm separate from libc. This must trail the generated
     // program and every native FFI input because GNU ld resolves archives
     // from left to right.
@@ -1068,6 +1070,7 @@ export async function compileCInternal(
     ...(mbedtls && targetPlatform(driver) === "win32" ? ["-lbcrypt"] : []),
     ...(tlsCa && targetPlatform(driver) === "win32" ? ["-lcrypt32"] : []),
     ...(((opts.zlib ?? false) || nativeFetch) && !isZigDriver(driver) ? ["-lz"] : []),
+    ...unwinderLinkArgs(driver),
     ...driver.linkArgs,
     ...executableLinkFlags,
   ];
@@ -1080,6 +1083,7 @@ export async function compileCInternal(
     ...(mbedtls && targetPlatform(driver) === "win32" ? ["-lbcrypt"] : []),
     ...(tlsCa && targetPlatform(driver) === "win32" ? ["-lcrypt32"] : []),
     ...(((opts.zlib ?? false) || nativeFetch) && !isZigDriver(driver) ? ["-lz"] : []),
+    ...unwinderLinkArgs(driver),
     ...driver.linkArgs,
     ...executableLinkFlags,
   ];
@@ -1689,3 +1693,11 @@ export async function compileC(opts: CcOptions): Promise<void> {
     await rm(`${opts.outPath}.dSYM`, { recursive: true, force: true });
   }
 }
+
+/** Linux runtimes raise through the native unwinder (scr_unwind_raise):
+ * Zig's libunwind, or the toolchain's libgcc_eh. Both are static archives,
+ * so programs load no shared library for them. */
+function unwinderLinkArgs(driver: CcDriver): string[] {
+  if (targetPlatform(driver) !== "linux") return [];
+  return isZigDriver(driver) ? ["-lunwind"] : ["-lgcc_eh"];
+}
diff --git a/packages/compiler/src/backend/native/runtime-inputs.ts b/packages/compiler/src/backend/native/runtime-inputs.ts
index c7c5bc32b..d32867331 100644
--- a/packages/compiler/src/backend/native/runtime-inputs.ts
+++ b/packages/compiler/src/backend/native/runtime-inputs.ts
@@ -53,6 +53,7 @@ export const EXECUTABLE_RUNTIME_SOURCES = [
   "scr_object.c",
   "scr_union.c",
   "scr_exception.c",
+  "scr_unwind.c",
   "scr_error.c",
   "scr_console.c",
   "scr_lib.c",
diff --git a/packages/compiler/src/index.ts b/packages/compiler/src/index.ts
index e2d1c97cc..4fb64968b 100644
--- a/packages/compiler/src/index.ts
+++ b/packages/compiler/src/index.ts
@@ -875,6 +875,7 @@ async function prepareExecutableInput(
       pointerBits: buildPlatform === "wasi" ? 32 : 64,
       wasi: buildPlatform === "wasi",
       runtimeAbiMarker: useRuntimePack,
+      unwindAbi: buildPlatform === "linux",
       objectAudit: opts.sanitize === true,
       lowRegion: lowRegionTarget(buildPlatform, opts.sanitize === true),
       ...(opts.sanitize === true ? { wasmBoundsChecks: true } : {}),
diff --git a/packages/compiler/src/native/prepare.ts b/packages/compiler/src/native/prepare.ts
index 7118e47b9..c15bfbf9b 100644
--- a/packages/compiler/src/native/prepare.ts
+++ b/packages/compiler/src/native/prepare.ts
@@ -408,6 +408,7 @@ export function prepareNativeExecutable(
           pointerBits: toolchain.target.pointerBits,
           wasi: toolchain.target.platform === "wasi",
           runtimeAbiMarker: outputKind === "obj" || outputKind === "exe",
+          unwindAbi: outputKind === "exe" && toolchain.target.platform === "linux",
           objectAudit: options.sanitize === true,
           lowRegion: lowRegionTarget(toolchain.target.platform, options.sanitize === true),
           functionWorkers: emitWorkers(),
diff --git a/packages/runtime-linux-arm64-gnu/scripts/build.mjs b/packages/runtime-linux-arm64-gnu/scripts/build.mjs
index 729c3fbb6..d16fb1528 100644
--- a/packages/runtime-linux-arm64-gnu/scripts/build.mjs
+++ b/packages/runtime-linux-arm64-gnu/scripts/build.mjs
@@ -24,6 +24,10 @@ process.env.SCRIPTC_RUNTIME_PACK_CONFIG = JSON.stringify({
   },
   ...toolchain,
   compileFlags: ["-ffunction-sections", "-fdata-sections"],
-  systemLibraries: [{ name: "m", predicate: true }],
+  // scr_unwind_raise: the static libgcc_eh, which loads no shared library.
+  systemLibraries: [
+    { name: "m", predicate: true },
+    { name: "gcc_eh", predicate: true },
+  ],
 });
 await import("../../runtime-pack-common/scripts/build.mjs");
diff --git a/packages/runtime-linux-arm64-musl/scripts/build.mjs b/packages/runtime-linux-arm64-musl/scripts/build.mjs
index 10635d857..6c9b38244 100644
--- a/packages/runtime-linux-arm64-musl/scripts/build.mjs
+++ b/packages/runtime-linux-arm64-musl/scripts/build.mjs
@@ -26,6 +26,10 @@ process.env.SCRIPTC_RUNTIME_PACK_CONFIG = JSON.stringify({
   },
   targetArgs: ["-target", "aarch64-linux-musl"],
   compileFlags: ["-ffunction-sections", "-fdata-sections"],
-  systemLibraries: [{ name: "m", predicate: true }],
+  // scr_unwind_raise: Zig's libunwind.
+  systemLibraries: [
+    { name: "m", predicate: true },
+    { name: "unwind", predicate: true },
+  ],
 });
 await import("../../runtime-pack-common/scripts/build.mjs");
diff --git a/packages/runtime-linux-x64-gnu/scripts/build.mjs b/packages/runtime-linux-x64-gnu/scripts/build.mjs
index 811bb537b..53df5f7e7 100644
--- a/packages/runtime-linux-x64-gnu/scripts/build.mjs
+++ b/packages/runtime-linux-x64-gnu/scripts/build.mjs
@@ -24,6 +24,10 @@ process.env.SCRIPTC_RUNTIME_PACK_CONFIG = JSON.stringify({
   },
   ...toolchain,
   compileFlags: ["-ffunction-sections", "-fdata-sections"],
-  systemLibraries: [{ name: "m", predicate: true }],
+  // scr_unwind_raise: the static libgcc_eh, which loads no shared library.
+  systemLibraries: [
+    { name: "m", predicate: true },
+    { name: "gcc_eh", predicate: true },
+  ],
 });
 await import("../../runtime-pack-common/scripts/build.mjs");
diff --git a/packages/runtime-linux-x64-musl/scripts/build.mjs b/packages/runtime-linux-x64-musl/scripts/build.mjs
index 33fc4c3d1..88538de76 100644
--- a/packages/runtime-linux-x64-musl/scripts/build.mjs
+++ b/packages/runtime-linux-x64-musl/scripts/build.mjs
@@ -26,6 +26,10 @@ process.env.SCRIPTC_RUNTIME_PACK_CONFIG = JSON.stringify({
   },
   targetArgs: ["-target", "x86_64-linux-musl"],
   compileFlags: ["-ffunction-sections", "-fdata-sections"],
-  systemLibraries: [{ name: "m", predicate: true }],
+  // scr_unwind_raise: Zig's libunwind.
+  systemLibraries: [
+    { name: "m", predicate: true },
+    { name: "unwind", predicate: true },
+  ],
 });
 await import("../../runtime-pack-common/scripts/build.mjs");
diff --git a/packages/runtime-pack-common/runtime-pack-matrix.mjs b/packages/runtime-pack-common/runtime-pack-matrix.mjs
index 600637ba6..4df534739 100644
--- a/packages/runtime-pack-common/runtime-pack-matrix.mjs
+++ b/packages/runtime-pack-common/runtime-pack-matrix.mjs
@@ -30,6 +30,7 @@ export const BASE_RUNTIME_SOURCES = [
   "scr_object.c",
   "scr_union.c",
   "scr_exception.c",
+  "scr_unwind.c",
   "scr_error.c",
   "scr_console.c",
   "scr_lib.c",
diff --git a/packages/runtime/src/scr_exception.h b/packages/runtime/src/scr_exception.h
index e99f84243..63dd4a3ca 100644
--- a/packages/runtime/src/scr_exception.h
+++ b/packages/runtime/src/scr_exception.h
@@ -123,6 +123,11 @@ static inline ScrExcCell *scr_exc_swap_cell_inline(ScrExcCell *cell) {
 _Static_assert(offsetof(ScrExcCell, kind) == 0 && sizeof(ScrExcKind) == 4 && SCR_EXC_NONE == 0,
                "the LLVM emitter's inline pending check loads an i32 kind at offset 0");
 
+/* Unwinds the native stack to the nearest landing pad of emitted code with
+ * the exception pending in the active cell (the unwinding ABI of emitted
+ * functions, unwind-abi.ts). Linux (glibc and musl) only; it never
+ * returns. */
+SCR_COLD _Noreturn void scr_unwind_raise(void);
 SCR_COLD void scr_throw_f64(double v);
 SCR_COLD void scr_throw_bool(bool v);
 SCR_COLD void scr_throw_str(ScrStr *v); /* takes ownership */
diff --git a/packages/runtime/src/scr_unwind.c b/packages/runtime/src/scr_unwind.c
new file mode 100644
index 000000000..50474e82e
--- /dev/null
+++ b/packages/runtime/src/scr_unwind.c
@@ -0,0 +1,83 @@
+/* scr_unwind_raise: the native unwind of the unwinding exception ABI of
+ * emitted functions (the compiler's unwind-abi.ts). Linux (glibc and musl)
+ * only; elsewhere this unit is empty. */
+#include "scr_runtime.h"
+
+#if defined(__linux__) && !defined(__ANDROID__) && !defined(__wasi__)
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unwind.h>
+
+/* Weak, so the runtime unit alone does not link the unwinder into every
+ * program: programs that raise reference the personality routine from
+ * their landing pads, and its unit references the unwinder's entry points,
+ * which link it in. */
+#pragma weak _Unwind_ForcedUnwind
+#pragma weak _Unwind_GetCFA
+
+#if defined(__SANITIZE_ADDRESS__)
+#define SCR_UNWIND_ASAN 1
+#elif defined(__has_feature)
+#if __has_feature(address_sanitizer)
+#define SCR_UNWIND_ASAN 1
+#endif
+#endif
+#ifdef SCR_UNWIND_ASAN
+#include <sanitizer/asan_interface.h>
+#endif
+
+#ifdef SCR_UNWIND_ASAN
+/* The lowest stack address the unwind has not cleared yet. The unwind
+ * outlives the frame that started it: landing pads resume it. */
+static SCR_TL uintptr_t scr_unwind_low;
+#endif
+
+/* Emitted landing pads are cleanups: they release the frame's references
+ * and then either take the exception (a handler of theirs, or a frame on
+ * the pending-flag ABI that returns with it pending) or resume the unwind.
+ * So the unwind is forced, a single pass through every landing pad; the
+ * exception itself stays in the active cell. */
+static _Unwind_Reason_Code scr_unwind_stop(int version, _Unwind_Action actions,
+                                           _Unwind_Exception_Class cls,
+                                           struct _Unwind_Exception *exc,
+                                           struct _Unwind_Context *context, void *arg) {
+  (void)version;
+  (void)cls;
+  (void)exc;
+#ifdef SCR_UNWIND_ASAN
+  /* The frames this unwind passes never return, so it clears their
+   * redzones' shadow itself. Emitted code calls scr_unwind_raise as an
+   * ordinary function: the sanitizer's hook before no-return calls needs
+   * stack bounds, which fiber stacks do not report. */
+  uintptr_t cfa = _Unwind_GetCFA(context);
+  if (cfa > scr_unwind_low) {
+    __asan_unpoison_memory_region((void *)scr_unwind_low, cfa - scr_unwind_low);
+    scr_unwind_low = cfa;
+  }
+#else
+  (void)context;
+#endif
+  (void)arg;
+  if (actions & _UA_END_OF_STACK) {
+    fputs("scriptc: an exception unwound past the program's outermost frame\n", stderr);
+    abort();
+  }
+  return _URC_NO_REASON;
+}
+
+static SCR_TL struct _Unwind_Exception scr_unwind_exception;
+
+void scr_unwind_raise(void) {
+  struct _Unwind_Exception *exc = &scr_unwind_exception;
+  memset(exc, 0, sizeof *exc);
+  exc->exception_class = 0x5343524950540000ull; /* "SCRIPT\0\0" */
+#ifdef SCR_UNWIND_ASAN
+  scr_unwind_low = (uintptr_t)__builtin_frame_address(0);
+#endif
+  if (_Unwind_ForcedUnwind != NULL) _Unwind_ForcedUnwind(exc, scr_unwind_stop, NULL);
+  fputs("scriptc: the native unwinder could not raise an exception\n", stderr);
+  abort();
+}
+#endif
diff --git a/scripts/zero-cost-compare.mjs b/scripts/zero-cost-compare.mjs
index a1ab3ca60..b23f61a0a 100644
--- a/scripts/zero-cost-compare.mjs
+++ b/scripts/zero-cost-compare.mjs
@@ -395,7 +395,9 @@ export function dynamicTierSymbols(names) {
  * bench/channel-messages and bench/worker-messages, added later, link them
  * through worker messages:
  * node:worker_threads values are dyn objects. bench/json-unions, added
- * later too, decodes JSON.parse trees. bench/dynamic-methods and
+ * later too, decodes JSON.parse trees. bench/throw-chains, also added
+ * later, tests caught values with `instanceof`, as bench/validate-errors
+ * does. bench/dynamic-methods and
  * bench/dynamic-properties are untyped JavaScript. Every other bench workload is fully typed and must link none. The gate and
  * tests/harness/bench-dynamic-tier.test.ts enforce that, and the test also
  * fails when a listed workload stops linking them, so remove a workload here
@@ -417,6 +419,7 @@ export const DYNAMIC_WORKLOADS = new Set([
   "bench/log-summary",
   "bench/inventory-report",
   "bench/json-unions",
+  "bench/throw-chains",
 ]);
 
 /** Names of the functions (text and weak symbols) in `nm` output. Mach-O