Message-ID: <5491BE7E.2060708@gmail.com>

  Date: Thu, 18 Dec 2014 01:33:50 +0800

  From: Wei-cheng Wang <cole945 at gmail dot com>

  To: Ulrich Weigand <uweigand at de dot ibm dot com>

  CC: gdb-patches at sourceware dot org

  Subject: Re: [PATCH 3/3 v2] Process record support for PowerPC

  On 2014/12/9 上午 03:13, Ulrich Weigand wrote:

  > Wei-cheng Wang wrote:

  >> 	    * ppc-linux-tdep.c (powerpc_linux_in_dynsym_resolve_code):

  >> 	    Scan PLT stub backward for reverse debugging.

  >> 	    (ppc_linux_init_abi): set powerpc_linux_in_dynsym_resolve_code

  >> 	    for both 32-bit and 64-bit.

  >

  > As I said in the reply to the 0/3 mail, I really think it would be

  > better to handle this within the PPC skip_trampoline_code implementation,

  > instead of having in_dynsym_resolve_code suddenly also cover the

  > trampolines ...

     Hi,

     See the new patch, I moved the for-loop into skip_trampoline_code,

     and removed in_dynsym_resolve_code.

  > It seems odd to have in_dynsym_resolve_code call into

  > skip_trampoline_code.  Is there a reason why the skip_trampoline_code

  > implementation cannot accept a PC in the middle of the sequence?

     I thought skip-trampoline is used to find the target address for

     inserting step-resume breakpoint, so it doesn't make sense for

     reverse-stepping, because we are just stepping from the target address.

     And for forward-stepping, when we reach the very first instruction of

     trampoline code, we can just skip the resolving code by inserting

     a step-resume breakpoint, so we don't have to step through the resolving

     code and check whether we are in the middle of trampoline code.

     in_dynsym_resolve_code is used to check whether we are in (the middle of)

     the resolving code, so we can keep going to step though the resolving code.

     Therefor I thought in_dynsym_resolve_code is the proper place to implement.

     Since skip-trampoline-code had implemented the plt-stub pattern-match code

     we need, by calling it in in-dynsym-resolve-code, we don't need to have

     duplicate pattern-match code in both functions.

  Wei-cheng,

  Thanks

  --

  2014-12-06  Wei-cheng Wang  <cole945@gmail.com>

	      * ppc-linux-tdep.c (ppc_skip_trampoline_code):

	      Scan PLT stub backward for reverse debugging.

	      * ppc64-tdep.c (ppc64_skip_trampoline_code): Likewise.

commit cf90fd9a07e8998540bf74f293d348a6653ac120

Author: Wei-cheng Wang <cole945@gmail.com>

Date:   Sat Jan 17 14:30:59 2015 +0800

    Skip-trampoline for PowerPC reverse-stepping.

Index: gdb-7.6.1/gdb/ppc64-tdep.c

===================================================================

--- gdb-7.6.1.orig/gdb/ppc64-tdep.c

+++ gdb-7.6.1/gdb/ppc64-tdep.c

@@ -20,6 +20,7 @@

 #include "defs.h"

 #include "frame.h"

 #include "gdbcore.h"

+#include "inferior.h"

 #include "ppc-tdep.h"

 #include "ppc64-tdep.h"

 #include "elf-bfd.h"

@@ -464,35 +465,66 @@ ppc64_skip_trampoline_code (struct frame

 				    ARRAY_SIZE (ppc64_standard_linkage8))))

 		     - 1];

   CORE_ADDR target;

+  int scan_limit, i;

-  if (ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage8, insns))

-    pc = ppc64_standard_linkage4_target (frame, pc, insns);

-  else if (ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage7, insns))

-    pc = ppc64_standard_linkage3_target (frame, pc, insns);

-  else if (ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage6, insns))

-    pc = ppc64_standard_linkage4_target (frame, pc, insns);

-  else if (ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage5, insns)

-	   && (insns[8] != 0 || insns[9] != 0))

-    pc = ppc64_standard_linkage3_target (frame, pc, insns);

-  else if (ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage4, insns)

-	   && (insns[9] != 0 || insns[10] != 0))

-    pc = ppc64_standard_linkage4_target (frame, pc, insns);

-  else if (ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage3, insns)

-	   && (insns[8] != 0 || insns[9] != 0))

-    pc = ppc64_standard_linkage3_target (frame, pc, insns);

-  else if (ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage2, insns)

-	   && (insns[10] != 0 || insns[11] != 0))

-    pc = ppc64_standard_linkage2_target (frame, pc, insns);

-  else if (ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage1, insns))

-    pc = ppc64_standard_linkage1_target (frame, pc, insns);

-  else

-    return 0;

-

-  /* The PLT descriptor will either point to the already resolved target

-     address, or else to a glink stub.  As the latter carry synthetic @plt

-     symbols, find_solib_trampoline_target should be able to resolve them.  */

-  target = find_solib_trampoline_target (frame, pc);

-  return target ? target : pc;

+  scan_limit = 1;

+  /* When reverse-debugging, scan backward to check whether we are

+     in the middle of trampoline code.  */

+  if (execution_direction == EXEC_REVERSE)

+    scan_limit = ARRAY_SIZE (insns) - 1;

+

+  for (i = 0; i < scan_limit; i++)

+    {

+      if (i < ARRAY_SIZE (ppc64_standard_linkage8) - 1

+	  && ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage8, insns))

+	pc = ppc64_standard_linkage4_target (frame, pc, insns);

+      else if (i < ARRAY_SIZE (ppc64_standard_linkage7) - 1

+	       && ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage7,

+					   insns))

+	pc = ppc64_standard_linkage3_target (frame, pc, insns);

+      else if (i < ARRAY_SIZE (ppc64_standard_linkage6) - 1

+	       && ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage6,

+					   insns))

+	pc = ppc64_standard_linkage4_target (frame, pc, insns);

+      else if (i < ARRAY_SIZE (ppc64_standard_linkage5) - 1

+	       && ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage5,

+					   insns)

+	       && (insns[8] != 0 || insns[9] != 0))

+	pc = ppc64_standard_linkage3_target (frame, pc, insns);

+      else if (i < ARRAY_SIZE (ppc64_standard_linkage4) - 1

+	       && ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage4,

+					   insns)

+	       && (insns[9] != 0 || insns[10] != 0))

+	pc = ppc64_standard_linkage4_target (frame, pc, insns);

+      else if (i < ARRAY_SIZE (ppc64_standard_linkage3) - 1

+	       && ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage3,

+					   insns)

+	       && (insns[8] != 0 || insns[9] != 0))

+	pc = ppc64_standard_linkage3_target (frame, pc, insns);

+      else if (i < ARRAY_SIZE (ppc64_standard_linkage2) - 1

+	       && ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage2,

+					   insns)

+	       && (insns[10] != 0 || insns[11] != 0))

+	pc = ppc64_standard_linkage2_target (frame, pc, insns);

+      else if (i < ARRAY_SIZE (ppc64_standard_linkage1) - 1

+	       && ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage1,

+					   insns))

+	pc = ppc64_standard_linkage1_target (frame, pc, insns);

+      else

+	{

+	  /* Scan backward one more instructions if doesn't match.  */

+	  pc -= 4;

+	  continue;

+	}

+

+      /* The PLT descriptor will either point to the already resolved target

+         address, or else to a glink stub.  As the latter carry synthetic @plt

+         symbols, find_solib_trampoline_target should be able to resolve them.  */

+      target = find_solib_trampoline_target (frame, pc);

+      return target ? target : pc;

+  }

+

+  return 0;

 }

 /* Support for convert_from_func_ptr_addr (ARCH, ADDR, TARG) on PPC64

Index: gdb-7.6.1/gdb/ppc-linux-tdep.c

===================================================================

--- gdb-7.6.1.orig/gdb/ppc-linux-tdep.c

+++ gdb-7.6.1/gdb/ppc-linux-tdep.c

@@ -52,6 +52,7 @@

 #include "linux-tdep.h"

 #include "linux-record.h"

 #include "record-full.h"

+#include "inferior.h"

 #include "stap-probe.h"

 #include "ax.h"

@@ -362,31 +363,50 @@ ppc_skip_trampoline_code (struct frame_i

   struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);

   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);

   CORE_ADDR target = 0;

+  int scan_limit, i;

-  if (ppc_insns_match_pattern (frame, pc, powerpc32_plt_stub, insnbuf))

-    {

-      /* Insn pattern is

-		lis   r11, xxxx

-		lwz   r11, xxxx(r11)

-	 Branch target is in r11.  */

-

-      target = (ppc_insn_d_field (insnbuf[0]) << 16)

-	| ppc_insn_d_field (insnbuf[1]);

-      target = read_memory_unsigned_integer (target, 4, byte_order);

-    }

+  scan_limit = 1;

+  /* When reverse-debugging, scan backward to check whether we are

+     in the middle of trampoline code.  */

+  if (execution_direction == EXEC_REVERSE)

+    scan_limit = 4;	/* At more 4 instructions.  */

-  if (ppc_insns_match_pattern (frame, pc, powerpc32_plt_stub_so, insnbuf))

+  for (i = 0; i < scan_limit; i++)

     {

-      /* Insn pattern is

-		lwz   r11, xxxx(r30)

-	 Branch target is in r11.  */

-

-      target = get_frame_register_unsigned (frame, tdep->ppc_gp0_regnum + 30)

-	       + ppc_insn_d_field (insnbuf[0]);

-      target = read_memory_unsigned_integer (target, 4, byte_order);

+      if (ppc_insns_match_pattern (frame, pc, powerpc32_plt_stub, insnbuf))

+	{

+	  /* Insn pattern is

+	     lis   r11, xxxx

+	     lwz   r11, xxxx(r11)

+	     Branch target is in r11.  */

+

+	  target = (ppc_insn_d_field (insnbuf[0]) << 16)

+		   | ppc_insn_d_field (insnbuf[1]);

+	  target = read_memory_unsigned_integer (target, 4, byte_order);

+	}

+      else if (ppc_insns_match_pattern (frame, pc, powerpc32_plt_stub_so,

+					insnbuf))

+	{

+	  /* Insn pattern is

+	     lwz   r11, xxxx(r30)

+	     Branch target is in r11.  */

+

+	  target = get_frame_register_unsigned (frame,

+						tdep->ppc_gp0_regnum + 30)

+		   + ppc_insn_d_field (insnbuf[0]);

+	  target = read_memory_unsigned_integer (target, 4, byte_order);

+	}

+      else

+	{

+	  /* Scan backward one more instructions if doesn't match.  */

+	  pc -= 4;

+	  continue;

+	}

+

+      return target;

     }

-  return target;

+  return 0;

 }

 /* Wrappers to handle Linux-only registers.  */