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Re: [RFC][patch] Allow to disassemble line.

On Thu, Oct 8, 2009 at 9:52 AM, Paul Pluzhnikov <> wrote:

> On Thu, Oct 8, 2009 at 9:23 AM, Daniel Jacobowitz <> wrote:
>> I'd mildly prefer changing the behavior of GDB - but only if we can
>> get an additional enhancement that I don't think we have yet: "*" at
>> the PC...
> That sounds good. I'll try to implement that.

Here my attempt to implement that.

I am guessing that it is flawed, as it possibly breaks something in MI
(which I don't understand yet).

It also breaks quite a few test cases -- I'll adjust expected patterns if
it is decided to go ahead with this.

I should say that from CLI perspective I like this very much. On x86,
often you need to examine 10 or so instructions before the crash point.

I usually do 'x/10i $pc-15' (as instruction size is not fixed), and then
"hunt" for the current PC in the resulting output. This patch makes it so
much easier:

(top) x/10i $pc-15
  0x54d212 <catch_errors+54>:   mov    -0x10(%rbp),%edi
  0x54d215 <catch_errors+57>:   mov    $0x1,%esi
  0x54d21a <catch_errors+62>:   callq  0x452c38 <__sigsetjmp@plt>
  0x54d21f <catch_errors+67>:   jmp    0x54d237 <catch_errors+91>
* 0x54d221 <catch_errors+69>:   mov    -0x30(%rbp),%rdi
  0x54d225 <catch_errors+73>:   mov    -0x28(%rbp),%rax
  0x54d229 <catch_errors+77>:   callq  *%rax
  0x54d22b <catch_errors+79>:   mov    %eax,-0x4(%rbp)
  0x54d22e <catch_errors+82>:   callq  0x54c9c0
  0x54d233 <catch_errors+87>:   test   %eax,%eax

I also like how 'disassemble-next-line on' works:

(top) set disassemble-next-line on
(top) ni
0x000000000054d225      510           val = func (func_args);
  0x000000000054d221 <catch_errors+69>:  48 8b 7d d0    mov    -0x30(%rbp),%rdi
* 0x000000000054d225 <catch_errors+73>:  48 8b 45 d8    mov    -0x28(%rbp),%rax
  0x000000000054d229 <catch_errors+77>:  ff d0  callq  *%rax
  0x000000000054d22b <catch_errors+79>:  89 45 fc       mov    %eax,-0x4(%rbp)
(top) ni
0x000000000054d229      510           val = func (func_args);
  0x000000000054d221 <catch_errors+69>:  48 8b 7d d0    mov    -0x30(%rbp),%rdi
  0x000000000054d225 <catch_errors+73>:  48 8b 45 d8    mov    -0x28(%rbp),%rax
* 0x000000000054d229 <catch_errors+77>:  ff d0  callq  *%rax
  0x000000000054d22b <catch_errors+79>:  89 45 fc       mov    %eax,-0x4(%rbp)

As well as how 'disas' works:

(top) disas
Dump of assembler code for function catch_errors:
  0x000000000054d1dc <catch_errors+0>:  push   %rbp
  0x000000000054d1dd <catch_errors+1>:  mov    %rsp,%rbp
  0x000000000054d1e0 <catch_errors+4>:  sub    $0x40,%rsp
  0x000000000054d1e4 <catch_errors+8>:  mov    %rdi,-0x28(%rbp)
  0x000000000054d1e8 <catch_errors+12>: mov    %rsi,-0x30(%rbp)
  0x000000000054d1ec <catch_errors+16>: mov    %rdx,-0x38(%rbp)
  0x000000000054d1f0 <catch_errors+20>: mov    %ecx,-0x3c(%rbp)
  0x000000000054d1f3 <catch_errors+23>: movl   $0x0,-0x4(%rbp)
  0x000000000054d1fa <catch_errors+30>: mov    0x56e1bf(%rip),%rdi
   # 0xabb3c0 <uiout>
  0x000000000054d201 <catch_errors+37>: mov    -0x3c(%rbp),%edx
  0x000000000054d204 <catch_errors+40>: lea    -0x20(%rbp),%rsi
  0x000000000054d208 <catch_errors+44>: callq  0x54c678
  0x000000000054d20d <catch_errors+49>: mov    %rax,-0x10(%rbp)
  0x000000000054d211 <catch_errors+53>: mov    -0x10(%rbp),%rdi
  0x000000000054d215 <catch_errors+57>: mov    $0x1,%esi
  0x000000000054d21a <catch_errors+62>: callq  0x452c38 <__sigsetjmp@plt>
  0x000000000054d21f <catch_errors+67>: jmp    0x54d237 <catch_errors+91>
  0x000000000054d221 <catch_errors+69>: mov    -0x30(%rbp),%rdi
  0x000000000054d225 <catch_errors+73>: mov    -0x28(%rbp),%rax
* 0x000000000054d229 <catch_errors+77>: callq  *%rax
  0x000000000054d22b <catch_errors+79>: mov    %eax,-0x4(%rbp)
  0x000000000054d22e <catch_errors+82>: callq  0x54c9c0
  0x000000000054d233 <catch_errors+87>: test   %eax,%eax
  0x000000000054d235 <catch_errors+89>: jne    0x54d221 <catch_errors+69>
  0x000000000054d237 <catch_errors+91>: callq  0x54c9b0
  0x000000000054d23c <catch_errors+96>: test   %eax,%eax
  0x000000000054d23e <catch_errors+98>: jne    0x54d22e <catch_errors+82>
  0x000000000054d240 <catch_errors+100>:        mov
0x593721(%rip),%rdi        # 0xae0968 <gdb_stderr>
  0x000000000054d247 <catch_errors+107>:        mov    -0x20(%rbp),%rdx
  0x000000000054d24b <catch_errors+111>:        mov    -0x18(%rbp),%rcx
  0x000000000054d24f <catch_errors+115>:        mov    -0x38(%rbp),%rsi
  0x000000000054d253 <catch_errors+119>:        callq  0x54cdea
  0x000000000054d258 <catch_errors+124>:        mov    -0x20(%rbp),%eax
  0x000000000054d25b <catch_errors+127>:        test   %eax,%eax
  0x000000000054d25d <catch_errors+129>:        je     0x54d268
  0x000000000054d25f <catch_errors+131>:        movl   $0x0,-0x40(%rbp)
  0x000000000054d266 <catch_errors+138>:        jmp    0x54d26e
  0x000000000054d268 <catch_errors+140>:        mov    -0x4(%rbp),%eax
  0x000000000054d26b <catch_errors+143>:        mov    %eax,-0x40(%rbp)
  0x000000000054d26e <catch_errors+146>:        mov    -0x40(%rbp),%eax
  0x000000000054d271 <catch_errors+149>:        leaveq
  0x000000000054d272 <catch_errors+150>:        retq
End of assembler dump.

Paul Pluzhnikov

2009-10-16  Paul Pluzhnikov  <>

	* defs.h (pc_prefix): New prototype.
	* disasm.c (dump_insns): Identify instruction address as such.
	* ui-out.c (ui_out_field_core_addr): Highlight current instruction.
	* printcmd.c (do_examine): Likewise.
	(pc_prefix, print_pc_prefix): New function.
	* stack.c (print_frame_info): Disassemble entire current line.

Attachment: gdb-disas-20091016.txt
Description: Text document

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