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Fix for unw_backtrace fast path does not work on x86_64 [https://github.com/libunwind/libunwind/issues/440]#444

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djwatson merged 2 commits into
libunwind:masterfrom
DataDog:gleocadie/fix-frame-caraterization
Dec 28, 2022
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@gleocadie

@gleocadie gleocadie commented Dec 8, 2022 •
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I recently it the issue describe in #440 .
This PR is an attempt to fix it.

@TannerFirl

TannerFirl commented Dec 15, 2022

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I see similar logic in arm and aarch64. Do we know if #440 also applies in these cases? Specifically:

src/aarch64/Gstash_frame.c:61:          || (rs->reg.where[FP] == DWARF_WHERE_CFAREL
src/aarch64/Gstash_frame.c:66:          || (rs->reg.where[LR] == DWARF_WHERE_CFAREL
src/aarch64/Gstash_frame.c:71:          || (rs->reg.where[SP] == DWARF_WHERE_CFAREL
src/aarch64/Gstash_frame.c:79:    if (rs->reg.where[FP] == DWARF_WHERE_CFAREL)
src/aarch64/Gstash_frame.c:81:    if (rs->reg.where[LR] == DWARF_WHERE_CFAREL)
src/aarch64/Gstash_frame.c:83:    if (rs->reg.where[SP] == DWARF_WHERE_CFAREL)
src/arm/Gstash_frame.c:61:          || (rs->reg.where[R7] == DWARF_WHERE_CFAREL
src/arm/Gstash_frame.c:66:          || (rs->reg.where[LR] == DWARF_WHERE_CFAREL
src/arm/Gstash_frame.c:71:          || (rs->reg.where[SP] == DWARF_WHERE_CFAREL
src/arm/Gstash_frame.c:79:    if (rs->reg.where[R7] == DWARF_WHERE_CFAREL)
src/arm/Gstash_frame.c:81:    if (rs->reg.where[LR] == DWARF_WHERE_CFAREL)
src/arm/Gstash_frame.c:83:    if (rs->reg.where[SP] == DWARF_WHERE_CFAREL)
src/dwarf/Gparser.c:193:          set_reg (sr, regnum, DWARF_WHERE_CFAREL, val * dci->data_align);
src/dwarf/Gparser.c:202:          set_reg (sr, regnum, DWARF_WHERE_CFAREL, val * dci->data_align);
src/dwarf/Gparser.c:211:          set_reg (sr, regnum, DWARF_WHERE_CFAREL, val * dci->data_align);
src/dwarf/Gparser.c:400:          set_reg (sr, regnum, DWARF_WHERE_CFAREL, ~(val * dci->data_align) + 1);
src/dwarf/Gparser.c:410:            set_reg (sr, regnum, DWARF_WHERE_CFAREL,
src/dwarf/Gparser.c:922:        case DWARF_WHERE_CFAREL:
src/x86_64/Gstash_frame.c:74:          || (rs->reg.where[RBP] == DWARF_WHERE_CFAREL
src/x86_64/Gstash_frame.c:79:          || (rs->reg.where[RSP] == DWARF_WHERE_CFAREL
src/x86_64/Gstash_frame.c:87:    if (rs->reg.where[RBP] == DWARF_WHERE_CFAREL)
src/x86_64/Gstash_frame.c:89:    if (rs->reg.where[RSP] == DWARF_WHERE_CFAREL)

@gleocadie

gleocadie commented Dec 15, 2022

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src/x86_64/Gstash_frame.c:74: || (rs->reg.where[RBP] == DWARF_WHERE_CFAREL
src/x86_64/Gstash_frame.c:79: || (rs->reg.where[RSP] == DWARF_WHERE_CFAREL
src/x86_64/Gstash_frame.c:87: if (rs->reg.where[RBP] == DWARF_WHERE_CFAREL)
src/x86_64/Gstash_frame.c:89: if (rs->reg.where[RSP] == DWARF_WHERE_CFAREL)

Good point, I was only focusing on x86_64. But according to the code, for Gstash_frame.c in arm and aarch64, we can do the same.
But for those arch, it will be a bit difficult for me to test (none available)
I'll see what I can do.

@TannerFirl

TannerFirl commented Dec 15, 2022

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But for those arch, it will be a bit difficult for me to test (none available)

I can test aarch changes.

Btw, I can confirm aarch fast backtrace is not working. with debug enabled and verbose logging, export UNW_DEBUG_LEVEL=1; make Ltest-bt.log I see:

	via backtrace():
 >unw_init_local_common: (cursor=0xffffffffb2a8)
 >uc_addr: Accessing VG register from context is not supported
 >_ULaarch64_tdep_trace: begin ip 0x400000083f48 cfa 0xffffffffae90
 >_ULaarch64_step: (cursor=0xffffffffb2a8, ip=0x0000400000083f48, cfa=0x0000ffffffffae90))
 >_ULaarch64_dwarf_search_unwind_table: e->fde_offset = aa0, segbase = 4000000a04e8, debug_frame_base = 0, fde_addr = 4000000a0f88
 >_ULaarch64_step: dwarf_step()=1
 >_ULaarch64_tdep_trace: returning -5, depth 0

@gleocadie

gleocadie commented Dec 15, 2022

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@TannerFirl thanks for your help

@djwatson

djwatson commented Dec 28, 2022

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Lgtm, thanks for the fix!

@djwatson
djwatson merged commit b0b4d98 into libunwind:master Dec 28, 2022
@gleocadie
gleocadie deleted the gleocadie/fix-frame-caraterization branch December 28, 2022 19:11
@TannerFirl TannerFirl mentioned this pull request Jan 4, 2023
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3 participants

@gleocadie @TannerFirl @djwatson