Re: [RFA] Deal with get ecs->stop_func_end fail

[Michael Snyder <msnyder@vmware.com>]

teawater wrote:
> Hi Michael,
> 
> I try a program and got:
> (gdb) start
> Temporary breakpoint 1 at 0x80483c1: file 1.c, line 20.
> Starting program: /media/disk/a.out
> 
> Temporary breakpoint 1, main () at 1.c:20
> 20             int     b = 0;
> (gdb) rec
> (gdb) n
> 21             int     c = 1;
> (gdb)
> 24              printf ("a = %d b = %d c = %d\n", a, b, c);
> (gdb)
> a = 0 b = 0 c = 1
> 25             b = cool ();
> (gdb) rn
> 
> No more reverse-execution history.
> main () at 1.c:20
> 20             int     b = 0;
> 
> 
> It's clear that "rn" got error.
> This is because:
>   find_pc_partial_function (stop_pc, &ecs->stop_func_name,
>                             &ecs->stop_func_start, &ecs->stop_func_end);
> This part get ecs->stop_func_end is 0.

Aha.  This is because we have stepped backward into
a shared-library trampoline.  You understand trampoline?

It means that this was the first time the program calls
"printf", which is in a shared library, so the program
jumps into a jump table which causes the dymanic runtime
resolver (ld-linux.so) to be called.

We actually succeeded in "nexting" backward through printf,
and then we succeeded in "nexting" backward thru _dl_runtime_resolver,
but we failed when we hit the trampoline (backward).

Give me some time, I need to figure out how to handle
trampolines backward!   ;-)

Meanwhile, this is obviously a problem in infrun, so
it does not need to affect your work on record/replay.

Leave this to me.   ;-)