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Improve backtraces

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We're now able to rewind the instruction pointer in x86 backtraces. This
helps ensure addr2line cannot print information about unrelated adjacent
code. I've restored -fno-schedule-insns2 in most cases because it really
does cause unpredictable breakage for backtraces.
This commit is contained in:
Justine Tunney 2024-05-30 15:11:45 -07:00
parent cd672e251f
commit 9b6718ac99
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11 changed files with 118 additions and 24 deletions
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37
libc/intrin/iscall.c Normal file
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/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi │
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2024 Justine Alexandra Roberts Tunney │
│ │
│ Permission to use, copy, modify, and/or distribute this software for │
│ any purpose with or without fee is hereby granted, provided that the │
│ above copyright notice and this permission notice appear in all copies. │
│ │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
│ PERFORMANCE OF THIS SOFTWARE. │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/intrin/iscall.internal.h"
// returns true if `p` is preceded by x86 call instruction
// this is actually impossible to do but we'll do our best
dontinstrument int __is_call(const unsigned char *p) {
if (p[-5] == 0xe8)
return 5; // call Jvds
if (p[-2] == 0xff && (p[-1] & 070) == 020)
return 2; // call %reg
if (p[-4] == 0xff && (p[-3] & 070) == 020)
return 4; // call disp8(%reg,%reg)
if (p[-3] == 0xff && (p[-2] & 070) == 020)
return 3; // call disp8(%reg)
if (p[-7] == 0xff && (p[-6] & 070) == 020)
return 7; // call disp32(%reg,%reg)
if (p[-6] == 0xff && (p[-5] & 070) == 020)
return 6; // call disp32(%reg)
return 0;
}