Bug 11833 - disassemble/m should be PC-driven, not source line driven
Summary: disassemble/m should be PC-driven, not source line driven
Alias: None
Product: gdb
Classification: Unclassified
Component: gdb (show other bugs)
Version: unknown
: P2 minor
Target Milestone: 7.1
Assignee: Not yet assigned to anyone
Depends on:
Reported: 2010-07-22 16:45 UTC by Jan Kratochvil
Modified: 2015-08-15 04:57 UTC (History)
4 users (show)

See Also:
Target: x86_64-unknown-linux-gnu
Last reconfirmed:


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Description Jan Kratochvil 2010-07-22 16:45:41 UTC
If you have -O2 code the source line <-> PC do not map linearly, they "jump".
objdump -dS displays the disassembly annotated by source lines.
GDB disass/m displays the source lines annotated by disassembly.
I find the objdump way better, in fact the only meaningful one.

GDB dump below displays PCs:
0x0, 0x1, 0xc, 0x7, 0xf, 0x11, 0x12.

f (void)
  extern int j;
  int i = j + 1;

  extern void g (void);
  return i;
gcc -O2 -g (gcc-4.4.4-10.fc13.x86_64)
objdump -dS
0000000000000000 <f>:
f (void)
   0:	53                   	push   %rbx
  extern int j;
  int i = j + 1;
   1:	8b 1d 00 00 00 00    	mov    0x0(%rip),%ebx        # 7 <f+0x7>

  extern void g (void);
   7:	e8 00 00 00 00       	callq  c <f+0xc>
f (void)
  extern int j;
  int i = j + 1;
   c:	83 c3 01             	add    $0x1,%ebx

  extern void g (void);
  return i;
   f:	89 d8                	mov    %ebx,%eax
  11:	5b                   	pop    %rbx
  12:	c3                   	retq   
(gdb) disass/m f
Dump of assembler code for function f:
3	{
   0x0000000000000000 <+0>:	push   %rbx

4	  extern int j;
5	  int i = j + 1;
   0x0000000000000001 <+1>:	mov    0x0(%rip),%ebx        # 0x7 <f+7>
   0x000000000000000c <+12>:	add    $0x1,%ebx

7	  extern void g (void);
8	  g();
   0x0000000000000007 <+7>:	callq  0xc <f+12>

9	  return i;
10	}
   0x000000000000000f <+15>:	mov    %ebx,%eax
   0x0000000000000011 <+17>:	pop    %rbx
   0x0000000000000012 <+18>:	retq   

End of assembler dump.
Comment 1 cvs-commit@gcc.gnu.org 2015-08-15 04:48:23 UTC
The master branch has been updated by Doug Evans <devans@sourceware.org>:


commit 6ff0ba5f7b8a2b10642bbb233a32043595c55670
Author: Doug Evans <xdje42@gmail.com>
Date:   Fri Aug 14 21:45:54 2015 -0700

    New /s modifier for the disassemble command.
    The "source centric" /m option to the disassemble command is often
    unhelpful, e.g., in the presence of optimized code.
    This patch adds a /s modifier that is better.
    For one, /m only prints instructions from the originating source file,
    leaving out instructions from e.g., inlined functions from other files.
    	PR gdb/11833
    	* NEWS: Document new /s modifier for the disassemble command.
    	* cli/cli-cmds.c (disassemble_command): Add support for /s.
    	(_initialize_cli_cmds): Update online docs of disassemble command.
    	* disasm.c: #include "source.h".
    	(struct deprecated_dis_line_entry): Renamed from dis_line_entry.
    	All uses updated.
    	(dis_line_entry): New struct.
    	(hash_dis_line_entry, eq_dis_line_entry): New functions.
    	(allocate_dis_line_table): New functions.
    	(maybe_add_dis_line_entry, line_has_code_p): New functions.
    	(dump_insns): New arg end_pc.  All callers updated.
    	(do_mixed_source_and_assembly_deprecated): Renamed from
    	do_mixed_source_and_assembly.  All callers updated.
    	(do_mixed_source_and_assembly): New function.
    	(gdb_disassembly): Handle /s (DISASSEMBLY_SOURCE).
    	* disasm.h (DISASSEMBLY_SOURCE_DEPRECATED): Renamed from
    	DISASSEMBLY_SOURCE.  All uses updated.
    	(DISASSEMBLY_SOURCE): New macro.
    	* mi/mi-cmd-disas.c (mi_cmd_disassemble): New modes 4,5.
    	* gdb.texinfo (Machine Code): Update docs for mixed source/assembly
    	(GDB/MI Data Manipulation): Update docs for new disassembly modes.
    	* gdb.mi/mi-disassemble.exp: Update.
    	* gdb.base/disasm-optim.S: New file.
    	* gdb.base/disasm-optim.c: New file.
    	* gdb.base/disasm-optim.h: New file.
    	* gdb.base/disasm-optim.exp: New file.
Comment 2 Doug Evans 2015-08-15 04:57:04 UTC
Patch committed.