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/* Signal frame backtracing support for SFrame on AARCH64.
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/aarch64/linux-unwind.h */
#include <signal.h>
#include <sys/ucontext.h>
#include <kernel_rt_sigframe.h>
#ifdef __AARCH64EL__
#define MOVZ_X8_8B 0xd2801168
#define SVC_0 0xd4000001
#else
#define MOVZ_X8_8B 0x681180d2
#define SVC_0 0x010000d4
#endif
#define MD_DECODE_SIGNAL_FRAME aarch64_decode_signal_frame
static _Unwind_Reason_Code
aarch64_decode_signal_frame (frame *frame)
{
unsigned int *pc = (unsigned int *) frame->pc;
mcontext_t *mt;
struct kernel_rt_sigframe *rt_;
if ((frame->pc & 3) != 0)
return _URC_END_OF_STACK;
/* A signal frame will have a return address pointing to
__kernel_rt_sigreturn. This code is hardwired as:
0xd2801168 movz x8, #0x8b
0xd4000001 svc 0x0
*/
if (pc[0] != MOVZ_X8_8B || pc[1] != SVC_0)
return _URC_END_OF_STACK;
rt_ = (struct kernel_rt_sigframe *) frame->sp;
mt = &rt_->uc.uc_mcontext;
/* Frame pointer register number. */
#define FP_REGNUM 30
frame->pc = (_Unwind_Ptr) mt->pc;
frame->sp = (_Unwind_Ptr) mt->sp;
frame->fp = (_Unwind_Ptr) mt->regs[FP_REGNUM];
return _URC_NO_REASON;
}
#define MD_DETECT_OUTERMOST_FRAME aarch64_detect_outermost_frame
static _Unwind_Reason_Code
aarch64_detect_outermost_frame (frame *frame)
{
/* Initial frame has LR and FP set to zero. We track only FP. */
if (frame->fp == 0)
return _URC_END_OF_STACK;
return _URC_NO_REASON;
}
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