Re: [Valgrind-users] unable to read core generated by valgrind in gdb / aarch64

[Tomas V. <tv...@fu...>]

On 9/9/22 18:20, John Reiser wrote:
> [[Aggressive snipping, but relevant details preserved.]]
> 
>> No threading is used. Postgres is multi-process, and uses shared 
>> memory for the shared cache (through shm_open etc.).
> 
> Multi-process plus shm_open() IS THREADING!  Not pthreads, but multiple
> execution contexts that read and write the same memory, which is
> subject to the same types of synchronization errors as pthreads.
> Perhaps --tool=drd and --tool=helgrind can help.
> 

OK, but why would that break core files only with valgrind? Because when 
ran directly, the core files work perfectly fine.

> 
> [[Another topic]]
>> Sure, but that's more of a workaround - it does not make the core file 
>> useful, it provides alternative way to get to the same result. Plus it 
>> requires additional tooling/scripting, and I'd prefer keeping the 
>> tooling as simple as possible.
> 
> I made a specific suggestion that takes less than one hour: build a 
> small test case
> that performs a short chain of subroutine calls, with the last routine 
> generating
> a deliberate SIGABRT.  Run the test case under valgrind, get a core file 
> from valgrind,
> and see if gdb gives the correct traceback from that core file.  The 
> objective
> is to provide a strong clue about whether *every* core file generated by 
> valgrind
> (in your environment) fails to work well with gdb.  Perhaps solving the 
> problem
> that involves your larger and more-complex case can be subsumed by 
> analyzing
> something that is much simpler.
> 
> Please perform that experiment and report the results here.
> 

I did this experiment - attached is a simple .c file, with a trivial 
example (3 functions) and segfault (or abort). When built like this:

   $ gcc valgrind-core-test.c -O0 -g

then the core file produced without valgrind is perfectly fine:

   $ gdb ./a.out core
   ...
   Core was generated by `./a.out'.
   Program terminated with signal SIGSEGV, Segmentation fault.
   #0  0x0000005594350734 in f3 () at valgrind-core-test.c:6
   6		*ptr = 'a';
   (gdb) bt
   #0  0x0000005594350734 in f3 () at valgrind-core-test.c:6
   #1  0x0000005594350750 in f2 () at valgrind-core-test.c:13
   #2  0x0000005594350768 in f1 () at valgrind-core-test.c:18
   #3  0x0000005594350780 in main () at valgrind-core-test.c:23

but when run under valgrind it looks like this:

   $ gdb ./a.out vgcore.1395835
   ...
   Core was generated by `'.
   Program terminated with signal SIGSEGV, Segmentation fault.
   #0  0x0000000000108734 in ?? ()
   (gdb) bt
   #0  0x0000000000108734 in ?? ()
   #1  0x0000000000108780 in ?? ()
   #2  0x0000000000108644 in ?? ()

However, when I do this on x86 (Fedora 34, gcc 11.3.1, valgrind 3.18.1) 
it works just fine and I get the same backtrace.

So perhaps this is specific to (either) gcc 10.2, or aarch64 platform.


regards
Tomas