Re: toolchain/50773: GDB single stepping fails for dynamically linked binary on armbe

[Rin Okuyama <rokuyama%rk.phys.keio.ac.jp@localhost>]

The following reply was made to PR toolchain/50773; it has been noted by GNATS.

From: Rin Okuyama <rokuyama%rk.phys.keio.ac.jp@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: toolchain/50773: GDB single stepping fails for dynamically linked
 binary on armbe
Date: Sun, 5 Jun 2016 01:04:15 +0900

 On 2016/06/02 3:31, Rin Okuyama wrote:
 > I observed the exactly same problem also on armel:
 >
 >   % uname -mpr
 >   7.99.30 evbarm earmv7hf
 (snip)
 
 Finally, I got it working! We need to skip symbol from ld.elf_so,
 as in the case of OpenBSD/arm. Then, single stepping works fine
 for dynamically linked binaries. I have tested both gdb (7.10) and
 gdb.old (7.9) both on evbearmv7hf-eb and -el. Please apply the
 attached patch below.
 
 Thanks,
 Rin
 
 --- src/external/gpl3/gdb.old/dist/gdb/armnbsd-tdep.c.orig	2016-06-04 22:18:36.500300231 +0900
 +++ src/external/gpl3/gdb.old/dist/gdb/armnbsd-tdep.c	2016-06-04 23:31:38.080675054 +0900
 @@ -19,6 +19,7 @@
   
   #include "defs.h"
   #include "osabi.h"
 +#include "objfiles.h"
   
   #include "arm-tdep.h"
   #include "solib-svr4.h"
 @@ -27,6 +28,8 @@
   #define ARM_NBSD_JB_PC 24
   #define ARM_NBSD_JB_ELEMENT_SIZE INT_REGISTER_SIZE
   
 +CORE_ADDR armnbsd_skip_solib_resolver (struct gdbarch *, CORE_ADDR);
 +
   /* For compatibility with previous implemenations of GDB on arm/NetBSD,
      override the default little-endian breakpoint.  */
   static const gdb_byte arm_nbsd_arm_le_breakpoint[] = {0x11, 0x00, 0x00, 0xe6};
 @@ -34,6 +37,19 @@
   static const gdb_byte arm_nbsd_thumb_le_breakpoint[] = {0xfe, 0xde};
   static const gdb_byte arm_nbsd_thumb_be_breakpoint[] = {0xde, 0xfe};
   
 +/* from obsd-tdep.c with symbol name adjusted to ours */
 +CORE_ADDR
 +armnbsd_skip_solib_resolver (struct gdbarch *gdbarch, CORE_ADDR pc)
 +{
 +  struct bound_minimal_symbol msym;
 +
 +  msym = lookup_minimal_symbol("_rtld_bind", NULL, NULL);
 +  if (msym.minsym && BMSYMBOL_VALUE_ADDRESS (msym) == pc)
 +    return frame_unwind_caller_pc (get_current_frame ());
 +  else
 +    return find_solib_trampoline_target (get_current_frame (), pc);
 +}
 +
   static void
   arm_netbsd_init_abi_common (struct gdbarch_info info,
   			    struct gdbarch *gdbarch)
 @@ -93,6 +109,9 @@
     /* NetBSD ELF uses SVR4-style shared libraries.  */
     set_solib_svr4_fetch_link_map_offsets
       (gdbarch, svr4_ilp32_fetch_link_map_offsets);
 +
 +  /* for single stepping; see PR/50773 */
 +  set_gdbarch_skip_solib_resolver (gdbarch, armnbsd_skip_solib_resolver);
   }
   
   static enum gdb_osabi
 --- src/external/gpl3/gdb/dist/gdb/armnbsd-tdep.c.orig	2016-06-04 22:22:13.446960426 +0900
 +++ src/external/gpl3/gdb/dist/gdb/armnbsd-tdep.c	2016-06-04 23:30:59.155155886 +0900
 @@ -19,6 +19,7 @@
   
   #include "defs.h"
   #include "osabi.h"
 +#include "objfiles.h"
   
   #include "arm-tdep.h"
   #include "solib-svr4.h"
 @@ -27,6 +28,8 @@
   #define ARM_NBSD_JB_PC 24
   #define ARM_NBSD_JB_ELEMENT_SIZE INT_REGISTER_SIZE
   
 +CORE_ADDR armnbsd_skip_solib_resolver (struct gdbarch *, CORE_ADDR);
 +
   /* For compatibility with previous implemenations of GDB on arm/NetBSD,
      override the default little-endian breakpoint.  */
   static const gdb_byte arm_nbsd_arm_le_breakpoint[] = {0x11, 0x00, 0x00, 0xe6};
 @@ -34,6 +37,19 @@
   static const gdb_byte arm_nbsd_thumb_le_breakpoint[] = {0xfe, 0xde};
   static const gdb_byte arm_nbsd_thumb_be_breakpoint[] = {0xde, 0xfe};
   
 +/* from obsd-tdep.c with symbol name adjusted to ours */
 +CORE_ADDR
 +armnbsd_skip_solib_resolver (struct gdbarch *gdbarch, CORE_ADDR pc)
 +{
 +  struct bound_minimal_symbol msym;
 +
 +  msym = lookup_minimal_symbol("_rtld_bind", NULL, NULL);
 +  if (msym.minsym && BMSYMBOL_VALUE_ADDRESS (msym) == pc)
 +    return frame_unwind_caller_pc (get_current_frame ());
 +  else
 +    return find_solib_trampoline_target (get_current_frame (), pc);
 +}
 +
   static void
   arm_netbsd_init_abi_common (struct gdbarch_info info,
   			    struct gdbarch *gdbarch)
 @@ -93,6 +109,9 @@
     /* NetBSD ELF uses SVR4-style shared libraries.  */
     set_solib_svr4_fetch_link_map_offsets
       (gdbarch, svr4_ilp32_fetch_link_map_offsets);
 +
 +  /* for single stepping; see PR/50773 */
 +  set_gdbarch_skip_solib_resolver (gdbarch, armnbsd_skip_solib_resolver);
   }
   
   static enum gdb_osabi