Re: [reverse/record] adjust_pc_after_break in reverse execution mode?

Michael Snyder
2008-10-30T21:21:26Z

OK, I'm with you now. Thanks a lot for clarifying. ;-)

Pedro Alves wrote:
> On Thursday 30 October 2008 15:54:34, Michael Snyder wrote:
>> Pedro, yes, but I can no longer get it to exhibit that behavior.
>> Can you?
>>
>
> Sure, see below.
>
> Head of ChangeLog:
>
> 2008-10-24 Michael Snyder <msnyder@vmware.com>
>
> * infrun.c (handle_inferior_event): Handle dynamic symbol
> resolution in reverse.
>
> Test app:
>
> 18 volatile int global_foo = 0;
> 19
> 20 int
> 21 main (int argc, char **argv)
> 22 {
> 23 asm ("nop"); /* 1st insn */
> 24 asm ("nop"); /* 2nd insn */
> 25 asm ("nop"); /* 3rd insn */
> 26 asm ("nop"); /* 4th insn */
> 27 if (!global_foo)
> 28 goto ahead;
> 29 asm ("nop"); /* 5th insn */
> 30 asm ("nop"); /* 6th insn */
> 31 asm ("nop"); /* 7th insn */
> 32 asm ("nop"); /* 8th insn */ <<<<< bkpt here
> 33 ahead:
> 34 asm ("nop"); /* 9th insn */ <<<<< and here
> 35 end:
> 36 return 0;
> 37 }
>
> Normal play:
>
>> ./gdb ./testsuite/gdb.base/decr-pc-rev
> GNU gdb (GDB) 6.8.50.20080930-cvs
> [...]
> (gdb) start
> Temporary breakpoint 1 at 0x8048382: file ../../../src/gdb/testsuite/gdb.base/decr-pc-rev.c, line 23.
> Starting program: /home/pedro/gdb/reverse-20080930-branch/build32/gdb/testsuite/gdb.base/decr-pc-rev
>
> Temporary breakpoint 1, main (argc=<value optimized out>, argv=<value optimized out>)
> at ../../../src/gdb/testsuite/gdb.base/decr-pc-rev.c:23
> 23 asm ("nop"); /* 1st insn */
> (gdb) b 32
> Breakpoint 2 at 0x8048392: file ../../../src/gdb/testsuite/gdb.base/decr-pc-rev.c, line 32.
> (gdb) b 34
> Breakpoint 3 at 0x8048393: file ../../../src/gdb/testsuite/gdb.base/decr-pc-rev.c, line 34.
> (gdb) c
> Continuing.
>
> Breakpoint 3, main (argc=<value optimized out>, argv=<value optimized out>)
> at ../../../src/gdb/testsuite/gdb.base/decr-pc-rev.c:34
> 34 in ../../../src/gdb/testsuite/gdb.base/decr-pc-rev.c
> (gdb) p $pc
> $1 = (void (*)()) 0x8048393 <main+31>
> (gdb)
>
> Ok, breakpoint 3 was hit (notice the goto at line 28, it's
> always executed because global_foo is always 0)
>
> --------
>
> Now the same, but while recording (replay exhibits the
> same symptom)
>
>> ./gdb ./testsuite/gdb.base/decr-pc-rev
> GNU gdb (GDB) 6.8.50.20080930-cvs
> [...]
> (gdb) start
> Temporary breakpoint 1 at 0x8048382: file ../../../src/gdb/testsuite/gdb.base/decr-pc-rev.c, line 23.
> Starting program: /home/pedro/gdb/reverse-20080930-branch/build32/gdb/testsuite/gdb.base/decr-pc-rev
>
> Temporary breakpoint 1, main (argc=<value optimized out>, argv=<value optimized out>)
> at ../../../src/gdb/testsuite/gdb.base/decr-pc-rev.c:23
> 23 asm ("nop"); /* 1st insn */
> (gdb) record
> ^^^^^^
> (gdb) c
> Continuing.
>
> Breakpoint 2, main (argc=<value optimized out>, argv=<value optimized out>)
> at ../../../src/gdb/testsuite/gdb.base/decr-pc-rev.c:32
> 32 in ../../../src/gdb/testsuite/gdb.base/decr-pc-rev.c
> (gdb) p $pc
> $1 = (void (*)()) 0x8048392 <main+30>
> (gdb)
>
> Breakpoint 3 should've been hit, not 2. The PC points at
> 0x8048392, but it should point at 0x8048393.
>
> Feels like we're going in circles. :-)
>
> --
> Pedro Alves