mirror of
https://github.com/vercel-labs/scriptc.git
synced 2026-11-02 07:43:42 +08:00
Chris Tate
d4fcd787a8
scr_unwind.c is linked into every Linux executable, and its references to _Unwind_ForcedUnwind and _Unwind_GetCFA pulled the unwinder out of libgcc_eh (or Zig's libunwind) even for programs that never raise, which grew a static hello world past its size ceiling. The references are now weak: programs that raise reference the personality routine from their landing pads, and its unit links the unwinder in.
84 lines
3.0 KiB
C
84 lines
3.0 KiB
C
/* scr_unwind_raise: the native unwind of the unwinding exception ABI of
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* emitted functions (the compiler's unwind-abi.ts). Linux (glibc and musl)
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* only; elsewhere this unit is empty. */
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#include "scr_runtime.h"
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#if defined(__linux__) && !defined(__ANDROID__) && !defined(__wasi__)
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#include <stdint.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unwind.h>
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/* Weak, so the runtime unit alone does not link the unwinder into every
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* program: programs that raise reference the personality routine from
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* their landing pads, and its unit references the unwinder's entry points,
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* which link it in. */
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#pragma weak _Unwind_ForcedUnwind
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#pragma weak _Unwind_GetCFA
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#if defined(__SANITIZE_ADDRESS__)
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#define SCR_UNWIND_ASAN 1
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#elif defined(__has_feature)
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#if __has_feature(address_sanitizer)
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#define SCR_UNWIND_ASAN 1
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#endif
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#endif
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#ifdef SCR_UNWIND_ASAN
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#include <sanitizer/asan_interface.h>
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#endif
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#ifdef SCR_UNWIND_ASAN
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/* The lowest stack address the unwind has not cleared yet. The unwind
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* outlives the frame that started it: landing pads resume it. */
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static SCR_TL uintptr_t scr_unwind_low;
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#endif
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/* Emitted landing pads are cleanups: they release the frame's references
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* and then either take the exception (a handler of theirs, or a frame on
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* the pending-flag ABI that returns with it pending) or resume the unwind.
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* So the unwind is forced, a single pass through every landing pad; the
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* exception itself stays in the active cell. */
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static _Unwind_Reason_Code scr_unwind_stop(int version, _Unwind_Action actions,
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_Unwind_Exception_Class cls,
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struct _Unwind_Exception *exc,
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struct _Unwind_Context *context, void *arg) {
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(void)version;
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(void)cls;
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(void)exc;
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#ifdef SCR_UNWIND_ASAN
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/* The frames this unwind passes never return, so it clears their
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* redzones' shadow itself. Emitted code calls scr_unwind_raise as an
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* ordinary function: the sanitizer's hook before no-return calls needs
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* stack bounds, which fiber stacks do not report. */
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uintptr_t cfa = _Unwind_GetCFA(context);
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if (cfa > scr_unwind_low) {
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__asan_unpoison_memory_region((void *)scr_unwind_low, cfa - scr_unwind_low);
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scr_unwind_low = cfa;
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}
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#else
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(void)context;
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#endif
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(void)arg;
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if (actions & _UA_END_OF_STACK) {
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fputs("scriptc: an exception unwound past the program's outermost frame\n", stderr);
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abort();
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}
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return _URC_NO_REASON;
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}
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static SCR_TL struct _Unwind_Exception scr_unwind_exception;
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void scr_unwind_raise(void) {
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struct _Unwind_Exception *exc = &scr_unwind_exception;
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memset(exc, 0, sizeof *exc);
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exc->exception_class = 0x5343524950540000ull; /* "SCRIPT\0\0" */
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#ifdef SCR_UNWIND_ASAN
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scr_unwind_low = (uintptr_t)__builtin_frame_address(0);
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#endif
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if (_Unwind_ForcedUnwind != NULL) _Unwind_ForcedUnwind(exc, scr_unwind_stop, NULL);
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fputs("scriptc: the native unwinder could not raise an exception\n", stderr);
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abort();
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}
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#endif
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