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/* Signal frame backtracing support for SFrame on AMD, x86-64 and x86.
Copyright (C) 2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public License
as published by the Free Software Foundation; either version 2.1 of
the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be
useful, but WITHOUT ANY WARRANTY; without even the implied warranty
of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
/* This code is inspired from libgcc's MD_FALLBACK_FRAME_STATE_FOR
implementation. See libgcc/config/i386/linux-unwind.h */
#include <signal.h>
#include <sys/ucontext.h>
#ifdef __x86_64__
/* SFrame is only supported by x86_64 targets. */
#define MD_DECODE_SIGNAL_FRAME x86_64_decode_signal_frame
#ifdef __LP64__
#define RT_SIGRETURN_SYSCALL 0x050f0000000fc0c7ULL
#else
#define RT_SIGRETURN_SYSCALL 0x050f40000201c0c7ULL
#endif
static _Unwind_Reason_Code
x86_64_decode_signal_frame (frame *frame)
{
unsigned char *pc = (unsigned char *) frame->pc;
mcontext_t *st;
unsigned char pc0 = *(unsigned char *)(pc + 0);
unsigned long long pc1;
memcpy (&pc1, pc + 1, sizeof (unsigned long long));
/* movq $__NR_rt_sigreturn, %rax ; syscall. */
if ( pc0 == 0x48
&& pc1 == RT_SIGRETURN_SYSCALL)
{
ucontext_t *uc_ = (ucontext_t *)frame->sp;
st = &uc_->uc_mcontext;
}
else
return _URC_END_OF_STACK;
frame->pc = (_Unwind_Ptr) st->gregs[REG_RIP];
frame->sp = (_Unwind_Ptr) st->gregs[REG_RSP];
frame->fp = (_Unwind_Ptr) st->gregs[REG_RBP];
return _URC_NO_REASON;
}
#define MD_DETECT_OUTERMOST_FRAME x86_64_detect_outermost_frame
static _Unwind_Reason_Code
x86_64_detect_outermost_frame (frame *frame)
{
/* Outermost frame has the frame pointer cleared. */
if (frame->fp == 0)
return _URC_END_OF_STACK;
return _URC_NO_REASON;
}
#endif /* ifdef __x86_64__ */
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