Re: [pushed] Change inline frame breakpoint skipping logic (fix gdb.gdb/selftest.exp)

Joel Brobecker
2018-06-25T21:04:44Z

Hello,

> gdb/ChangeLog:
> 2018-06-19 Pedro Alves <palves@redhat.com>
>
> * inline-frame.c (stopped_by_user_bp_inline_frame): Replace PC
> parameter with a block parameter. Compare location's block symbol
> with the frame's block instead of addresses.
> (skip_inline_frames): Pass the current block instead of the
> frame's address. Break out as soon as we determine the frame
> should not be skipped.
>
> gdb/testsuite/ChangeLog:
> 2018-06-19 Pedro Alves <palves@redhat.com>
>
> * gdb.opt/inline-break.c (func_inline_callee, func_inline_caller)
> (func_extern_caller): New.
> (main): Call func_extern_caller.
> * gdb.opt/inline-break.exp: Add tests for inline frame skipping
> logic change.

it looks like this patch is causing a crash with the following
example program:

$ cat -n r.h
1 /* r.h */
2 int counter = 42;
3
4 inline void
5 callee () {
6 counter = 0; /* break here */
7 }
$ cat -n r.c
1 /* r.c */
2 #include "r.h"
3
4 int
5 main ()
6 {
7 callee ();
8 }

I compiled it using the following commands:

$ gcc -c -g -O2 r.c
$ gcc -o r r.o

Then, trying to put a breakpoint on r.h:6 (inside "callee") causes
a SEGV for me:

$ gdb -q r
Reading symbols from r...done.
(gdb) b r.h:6
Breakpoint 1 at 0x4003c0: file r.h, line 6.
(gdb) run
Starting program: /[...]/r
[1] 75618 segmentation fault /[...]/gdb -q r

Prior to this commit, the behavior is the following for the "run"
command:

(gdb) run
Starting program: /[...]/r

Breakpoint 1, callee () at r.h:6
6 counter = 0; /* break here */

The problem occurs because we apparently assume that a bp_location's
symbols is not NULL:

Program received signal SIGSEGV, Segmentation fault.
0x00000000006f42bb in stopped_by_user_bp_inline_frame (
stop_chain=<optimized out>, frame_block=<optimized out>)
at /homes/brobecke/act/gdb/gdb-head/gdb/inline-frame.c:305
305 && frame_block == SYMBOL_BLOCK_VALUE (loc->symbol))
(gdb) p loc->symbol
$1 = (const symbol *) 0x0

I don't know yet whether that's a valid assumption or something
occurred earlier in the process. Any thoughts on this before I start
looking deeper?

I'm using a version of GCC 7.3.1 on x86_64-linux if anyone wants to
reproduce.

--
Joel