Get Different Result for the same core file with different versions of gdb.

[Simon Marchi]

On 2021-02-01 9:15 p.m., Andy Fan via Gdb wrote:
> On Mon, Feb 1, 2021 at 11:57 AM Andy Fan <zhihui.fan1213@gmail.com> wrote:
> 
>> Hi:
>>
>> You can pay attention to $2 and $3.They check the same addr in the same
>> core file.
>> I'm sure I am debugging the same file in the same machine.
>>
>> GDB 7.6:
>>
>> (gdb) up 3
>> #3  ResetPlanCache () at plancache.c:1922
>> 1922 plancache.c: No such file or directory.
>> (gdb) p ((AllocSet)plansource->query_context)->freelist
>> $1 = {0x0, *0x5bdd3b8*, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}
>> (gdb) p *((AllocSet)plansource->query_context)->freelist[1]
>> *$2 = {size = 10649824, aset = 0xa283c0 <AllocSetFree>}*
>> (gdb) p plansource->query_context->name
>> *$3 = 0xbfd929 "unnamed prepared statement"*
>> (gdb) x /10c plansource->query_context->name
>> 0xbfd929: 117 'u' 110 'n' 110 'n' 97 'a' 109 'm' 101 'e' 100 'd' 32 ' '
>> 0xbfd931: 112 'p' 114 'r'
>> (gdb) quit
>>
>>
>> GDB  9.2:
>> (gdb) up 3
>> #3  ResetPlanCache () at plancache.c:1922
>> 1922 plancache.c: No such file or directory.
>> (gdb) p ((AllocSet)plansource->query_context)->freelist
>> $1 = {0x0, *0x5bdd3b8*, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}
>> (gdb) p *((AllocSet)plansource->query_context)->freelist[1]
>> *$2 = {size = 16, aset = 0x0}*
>> (gdb) p plansource->query_context->name
>> *$3 = 0xbfd929 ""*
>> (gdb) x /10c plansource->query_context->name
>> 0xbfd929: 0 '\000' 0 '\000' 0 '\000' 0 '\000' 0 '\000' 0 '\000' 0 '\000' 0
>> '\000'
>> 0xbfd931: 0 '\000' 0 '\000'
>>
>>
>> Any ideas? Thanks!
>>
>> --
>> Best Regards
>> Andy Fan
>>
> 
> Will it have something with compiler?  The compiler I used
> to build the software (which generated the core file) is LLVM 6.0.0.

At first glance, it sounds like a bug.  Can you provide a reproducer?

Simon