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https://github.com/vercel-labs/scriptc.git
synced 2026-11-02 07:43:42 +08:00
Chris Tate
d5ac31f812
scr_unwind_raise walks the stack with plans cached per return address. The first raise through a return address finds the function's FDE through the .eh_frame_hdr of the object that contains it, runs the CFI up to the call, and finds the call site's landing pad in the LSDA; the plan records the frame's CFA rule, where its callee-saved registers are saved, and the landing pad. Later raises look the plans up, restore the registers, and jump to the first landing pad. Plans are inserted under a lock and read without one. Landing pads continue the unwind with scr_unwind_resume instead of `resume`, so the walk goes on from their frame. A frame whose CFI, pointer encodings or personality the plans do not express, or a return address without an FDE, leaves the unwind to libgcc's forced unwind from the frame the walk started at, as before. Other Linux targets keep libgcc's unwinder; their scr_unwind_resume calls _Unwind_Resume. bench:runtime gains layered-errors, a workload whose errors are thrown below small functions that hold references and caught per entry in a loop, and the corpus gains unwind-landing-pad-chains, which pins landing pads that continue the unwind, including in frames LLVM inlines into a caller whose handler takes the exception.
102 lines
2.3 KiB
ArmAsm
102 lines
2.3 KiB
ArmAsm
/* Frames for test_unwind.c with CFI that compilers emit rarely. Like the
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* frames in test_unwind_frames.ll, each takes a chain and calls its first
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* function with the rest. */
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.text
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/* Saves rbx and r12, and leaves through an early epilogue under
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* remember_state before its call, so the call's rules come from
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* restore_state. */
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.globl asm_remember
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.type asm_remember,@function
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asm_remember:
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.cfi_startproc
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pushq %rbx
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.cfi_def_cfa_offset 16
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.cfi_offset %rbx, -16
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pushq %r12
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.cfi_def_cfa_offset 24
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.cfi_offset %r12, -24
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subq $8, %rsp
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.cfi_def_cfa_offset 32
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movq (%rdi), %rax
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testq %rax, %rax
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jne 1f
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.cfi_remember_state
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addq $8, %rsp
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.cfi_def_cfa_offset 24
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popq %r12
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.cfi_def_cfa_offset 16
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.cfi_restore %r12
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popq %rbx
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.cfi_def_cfa_offset 8
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.cfi_restore %rbx
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retq
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.cfi_restore_state
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1:
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movabsq $0x5151515151515151, %rbx
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movabsq $0x5252525252525252, %r12
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addq $8, %rdi
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callq *%rax
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addq $8, %rsp
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.cfi_def_cfa_offset 24
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popq %r12
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.cfi_def_cfa_offset 16
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popq %rbx
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.cfi_def_cfa_offset 8
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retq
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.cfi_endproc
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.size asm_remember, .-asm_remember
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/* An rbp frame that saves r13 and r14 below rbp and moves the stack
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* pointer by an amount that depends on the chain's address. */
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.globl asm_rbp
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.type asm_rbp,@function
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asm_rbp:
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.cfi_startproc
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pushq %rbp
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.cfi_def_cfa_offset 16
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.cfi_offset %rbp, -16
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movq %rsp, %rbp
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.cfi_def_cfa_register %rbp
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pushq %r13
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pushq %r14
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.cfi_offset %r13, -24
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.cfi_offset %r14, -32
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movq %rdi, %rax
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andq $0x70, %rax
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subq %rax, %rsp
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movabsq $0x5353535353535353, %r13
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movabsq $0x5454545454545454, %r14
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movq (%rdi), %rax
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addq $8, %rdi
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callq *%rax
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leaq -16(%rbp), %rsp
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popq %r14
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popq %r13
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popq %rbp
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.cfi_def_cfa %rsp, 8
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retq
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.cfi_endproc
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.size asm_rbp, .-asm_rbp
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/* Defines its CFA with a DWARF expression (rsp + 16), which the plans do
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* not express: raises through it go to libgcc's unwinder. */
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.globl asm_expr
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.type asm_expr,@function
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asm_expr:
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.cfi_startproc
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pushq %rbx
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.cfi_escape 0x0f, 0x02, 0x77, 0x10
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.cfi_offset %rbx, -16
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movabsq $0x5555555555555555, %rbx
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movq (%rdi), %rax
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addq $8, %rdi
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callq *%rax
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popq %rbx
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.cfi_def_cfa %rsp, 8
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retq
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.cfi_endproc
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.size asm_expr, .-asm_expr
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.section .note.GNU-stack,"",@progbits
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