Re: devel/gdb: Fix backtrace across signals on amd64

On Mon, 2020-05-18 at 20:28 -0400, kurt@intricatesoftware.com wrote:
> Fix backtrace across signals on amd64
>
> The 'Apply the retpoline transformation to indirect jumps in the
> raw ASM' commit in 6.4 added an instruction to the sigcode.
> This fixes the offset to look for sigreturn and mantains
> backward compat till 5.0.
>
> okay?

ping

>
> Index: Makefile
> ===================================================================
> RCS file: /cvs/ports/devel/gdb/Makefile,v
> retrieving revision 1.65
> diff -u -p -u -r1.65 Makefile
> --- Makefile 29 Mar 2020 17:23:30 -0000 1.65
> +++ Makefile 18 May 2020 21:44:42 -0000
> @@ -4,7 +4,7 @@ COMMENT= GNU debugger
>  CATEGORIES= devel
>  
>  DISTNAME= gdb-7.12.1
> -REVISION= 10
> +REVISION= 11
>  
>  HOMEPAGE= https://www.gnu.org/software/gdb/
>  
> Index: patches/patch-gdb_amd64obsd-tdep_c
> ===================================================================
> RCS file: patches/patch-gdb_amd64obsd-tdep_c
> diff -N patches/patch-gdb_amd64obsd-tdep_c
> --- /dev/null 1 Jan 1970 00:00:00 -0000
> +++ patches/patch-gdb_amd64obsd-tdep_c 18 May 2020 21:44:42 -0000
> @@ -0,0 +1,107 @@
> +$OpenBSD$
> +
> +Index: gdb/amd64obsd-tdep.c
> +--- gdb/amd64obsd-tdep.c.orig
> ++++ gdb/amd64obsd-tdep.c
> +@@ -76,8 +76,40 @@ amd64obsd_iterate_over_regset_sections (struct gdbarch
> + /* Support for signal handlers.  */
> + 
> + /* Default page size.  */
> +-static const int amd64obsd_page_size = 4096;
> ++static const CORE_ADDR amd64obsd_page_size = 4096;
> + 
> ++/* Offset & instructions for sigreturn(2).  */
> ++
> ++#define SIGRETURN_INSN_LEN 9
> ++
> ++struct amd64obsd_sigreturn_info_t {
> ++  int offset;
> ++  gdb_byte sigreturn[SIGRETURN_INSN_LEN];
> ++}; 
> ++
> ++static const amd64obsd_sigreturn_info_t
> ++  amd64obsd_sigreturn_info[] = {
> ++  /* OpenBSD 6.4 */
> ++  { 9, { 0x48, 0xc7, 0xc0,
> ++         0x67, 0x00, 0x00, 0x00, /* movq $SYS_sigreturn, %rax */
> ++         0x0f, 0x05 } },         /* syscall */
> ++  /* OpenBSD 5.1 */
> ++  { 6, { 0x48, 0xc7, 0xc0,
> ++         0x67, 0x00, 0x00, 0x00, /* movq $SYS_sigreturn, %rax */
> ++         0x0f, 0x05 } },         /* syscall */
> ++  { 7, { 0x48, 0xc7, 0xc0,
> ++         0x67, 0x00, 0x00, 0x00, /* movq $SYS_sigreturn, %rax */
> ++         0x0f, 0x05 } },         /* syscall */
> ++  /* OpenBSD 5.0 */
> ++  { 6, { 0x48, 0xc7, 0xc0,
> ++         0x67, 0x00, 0x00, 0x00, /* movq $SYS_sigreturn, %rax */
> ++         0xcd, 0x80 } },         /* int $0x80 */
> ++  { 7, { 0x48, 0xc7, 0xc0,
> ++         0x67, 0x00, 0x00, 0x00, /* movq $SYS_sigreturn, %rax */
> ++         0xcd, 0x80 } },         /* int $0x80 */
> ++  { -1, {} }
> ++};
> ++
> + /* Return whether THIS_FRAME corresponds to an OpenBSD sigtramp
> +    routine.  */
> + 
> +@@ -86,20 +118,8 @@ amd64obsd_sigtramp_p (struct frame_info *this_frame)
> + {
> +   CORE_ADDR pc = get_frame_pc (this_frame);
> +   CORE_ADDR start_pc = (pc & ~(amd64obsd_page_size - 1));
> +-  const gdb_byte osigreturn[] =
> +-  {
> +-    0x48, 0xc7, 0xc0,
> +-    0x67, 0x00, 0x00, 0x00, /* movq $SYS_sigreturn, %rax */
> +-    0xcd, 0x80 /* int $0x80 */
> +-  };
> +-  const gdb_byte sigreturn[] =
> +-  {
> +-    0x48, 0xc7, 0xc0,
> +-    0x67, 0x00, 0x00, 0x00, /* movq $SYS_sigreturn, %rax */
> +-    0x0f, 0x05 /* syscall */
> +-  };
> +-  size_t buflen = (sizeof sigreturn) + 1;
> +-  gdb_byte *buf;
> ++  const amd64obsd_sigreturn_info_t *info;
> ++  gdb_byte buf[SIGRETURN_INSN_LEN];
> +   const char *name;
> + 
> +   /* If the function has a valid symbol name, it isn't a
> +@@ -113,22 +133,22 @@ amd64obsd_sigtramp_p (struct frame_info *this_frame)
> +   if (find_pc_section (pc) != NULL)
> +     return 0;
> + 
> +-  /* If we can't read the instructions at START_PC, return zero.  */
> +-  buf = (gdb_byte *) alloca ((sizeof sigreturn) + 1);
> +-  if (!safe_frame_unwind_memory (this_frame, start_pc + 6, buf, buflen))
> +-    return 0;
> ++  for (info = amd64obsd_sigreturn_info; info->offset != -1; info++)
> ++    {
> + 
> +-  /* Check for sigreturn(2).  Depending on how the assembler encoded
> +-     the `movq %rsp, %rdi' instruction, the code starts at offset 6 or
> +-     7.  OpenBSD 5.0 and later use the `syscall' instruction.  Older
> +-     versions use `int $0x80'.  Check for both.  */
> +-  if (memcmp (buf, sigreturn, sizeof sigreturn)
> +-      && memcmp (buf + 1, sigreturn, sizeof sigreturn)
> +-      && memcmp (buf, osigreturn, sizeof osigreturn)
> +-      && memcmp (buf + 1, osigreturn, sizeof osigreturn))
> +-    return 0;
> ++      /* If we can't read the instructions at return zero.  */
> ++      if (!safe_frame_unwind_memory (this_frame,
> ++        start_pc + info->offset, buf, sizeof buf))
> ++        continue;
> + 
> +-  return 1;
> ++      /* Check for sigreturn(2).  */
> ++      if (memcmp (buf, info->sigreturn, sizeof buf))
> ++        continue;
> ++
> ++      return 1;
> ++    }
> ++
> ++  return 0;
> + }
> + 
> + /* Assuming THIS_FRAME is for a BSD sigtramp routine, return the