Re: reverse execution

[Jan Kratochvil <jan.kratochvil@redhat.com>]

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On Mon, 08 Apr 2013 16:34:37 +0200, ishare wrote:
> I record at 0x40000000 , then I nexti 10 instructions , then I want reverse execute 
> these 10 instructions one by one, So I type reverse-nexti ,but unexpectly ,gdb directly
> goes back to the addresss 0x40000000 ,where I start record .
> 
> What I need is 10->9->8->7->6->5->4->3->2->1 ,not execute again from begin to end .

It is safer during troubleshooting to use *stepi instead of *nexti (where
there is no difference as there is no call instruction).

It works for me with 7.5.1 so it would be needed to have a reproducer.

Additionally there ware some 7.6 (pre-release available now) fixes to these
issues but it should not affect this case as long as there are no calls.


Regards,
Jan


GNU gdb (GDB) 7.5.1.20130125-cvs
Copyright (C) 2012 Free Software Foundation, Inc.
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This GDB was configured as "x86_64-unknown-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/jkratoch/t/nops...done.
(gdb) disas _start
Dump of assembler code for function _start:
   0x00000000004000d4 <+0>:	nop
   0x00000000004000d5 <+1>:	nop
   0x00000000004000d6 <+2>:	nop
   0x00000000004000d7 <+3>:	nop
   0x00000000004000d8 <+4>:	nop
   0x00000000004000d9 <+5>:	nop
   0x00000000004000da <+6>:	nop
   0x00000000004000db <+7>:	nop
   0x00000000004000dc <+8>:	nop
   0x00000000004000dd <+9>:	nop
   0x00000000004000de <+10>:	int3   
End of assembler dump.
(gdb) info files 
Symbols from "/home/jkratoch/t/nops".
Local exec file:
	`/home/jkratoch/t/nops', file type elf64-x86-64.
	Entry point: 0x4000d4
	0x00000000004000b0 - 0x00000000004000d4 is .note.gnu.build-id
	0x00000000004000d4 - 0x00000000004000df is .text
(gdb) b *0x4000d4
Breakpoint 1 at 0x4000d4: file nops.S, line 2.
(gdb) r
Starting program: /home/jkratoch/t/nops 
warning: no loadable sections found in added symbol-file system-supplied DSO at 0x7ffff7ffd000

Breakpoint 1, _start () at nops.S:2
2	nop
(gdb) record 
(gdb) nexti
3	nop
(gdb) 
4	nop
(gdb) 
5	nop
(gdb) 
6	nop
(gdb) 
7	nop
(gdb) 
8	nop
(gdb) 
9	nop
(gdb) 
10	nop
(gdb) 
11	nop
(gdb) 
12	int3
(gdb) reverse-nexti
11	nop
(gdb) 
10	nop
(gdb) 
9	nop
(gdb) 
8	nop
(gdb) 
7	nop
(gdb) 
6	nop
(gdb) 
5	nop
(gdb) 
4	nop
(gdb) 
3	nop
(gdb) 

No more reverse-execution history.
_start () at nops.S:2
2	nop
(gdb) 

[-- Attachment #2: nops.S --]
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_start: .globl _start
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
int3