x86: Add SFrame support for x86 architecture

The SFrame is well supported by x86 architecture since binutils 2.41.
Enable it to be used as default frame tracer.

Signed-off-by: Claudiu Zissulescu <claudiu.zissulescu-ianculescu@oracle.com>
Reviewed-by: DJ Delorie <dj@redhat.com>

diff --git a/sysdeps/unix/sysv/linux/x86_64/uw-sigframe.h b/sysdeps/unix/sysv/linux/x86_64/uw-sigframe.h
new file mode 100644 (file)
index 0000000..585ca01
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86_64/uw-sigframe.h
@@ -0,0 +1,76 @@
+/* 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__  */