[Bug gdb/16481] New: Python finish breakpoint does not work with a mix of inlined and tailcalled functions

["simon.marchi at polymtl dot ca" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=16481

            Bug ID: 16481
           Summary: Python finish breakpoint does not work with a mix of
                    inlined and tailcalled functions
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: simon.marchi at polymtl dot ca

This may seem a little far fetched, but I hit this while trying to track memory
allocations with a python script. I put a Python breakpoint on __libc_malloc,
which in turn sets a finish breakpoint so that I can get the pointer to the
allocated region. I noticed that some times, the finish breakpoint is never
hit.

I put up a very simple test case here:
  https://gist.github.com/simark/8548964

Compile with
  $ gcc -g test.c -O3

Run with
  $ gdb -x finish.py a.out

As the name describe, hopefully_inlined is inlined, hopefully_tailcalled is
tailcalled (did I just invent a verb?).

The python script sets a breakpoint on the hopefully_notinlined function, which
instanciantes a finish breakpoint. On exit of the function, we should see "I am
here", but we don't.

I diagnosed the problem, and something wrong seems to happen here:
 
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=gdb/breakpoint.c;h=c8e7e8842e2ed418d78b23c466018c88bb5e2aae;hb=HEAD#l5172

>From what I understand, for kinds of breakpoints where it makes sens, GDB
checks that the current stack frame is the same as when the breakpoint was set.
For the breakpoint to cause a stop, they have to match. The comparison in this
case returns false. One of the frames has its artifical_depth to zero while the
other has it to one. I am not sure which one is right, but I think that they
should be equal...

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