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I ran into a GDB crash in gdb.base/bp-cmds-continue-ctrl-c.exp in my
multi-target branch, which turns out exposed a bug that exists in
master too.
That testcase has a breakpoint with a "continue" command associated.
Then the breakpoint is constantly being hit. At the same time, the
testcase is continualy interrupting the program with Ctrl-C, and
re-resuming it, in a loop.
Running that testcase manually under Valgrind, after a few sequences
of 'Ctrl-C' + 'continue', I got:
Breakpoint 1, Quit
(gdb) ==21270== Invalid read of size 8
==21270== at 0x4D8185: pyuw_this_id(frame_info*, void**, frame_id*) (py-unwind.c:461)
==21270== by 0x6D426A: compute_frame_id(frame_info*) (frame.c:505)
==21270== by 0x6D43B7: get_frame_id(frame_info*) (frame.c:537)
==21270== by 0x84F3B8: scoped_restore_current_thread::scoped_restore_current_thread() (thread.c:1678)
==21270== by 0x718E3D: fetch_inferior_event(void*) (infrun.c:4076)
==21270== by 0x7067C9: inferior_event_handler(inferior_event_type, void*) (inf-loop.c:43)
==21270== by 0x45BEF9: handle_target_event(int, void*) (linux-nat.c:4419)
==21270== by 0x6C4255: handle_file_event(file_handler*, int) (event-loop.c:733)
==21270== by 0x6C47F8: gdb_wait_for_event(int) (event-loop.c:859)
==21270== by 0x6C3666: gdb_do_one_event() (event-loop.c:322)
==21270== by 0x6C3712: start_event_loop() (event-loop.c:371)
==21270== by 0x746801: captured_command_loop() (main.c:329)
==21270== Address 0x0 is not stack'd, malloc'd or (recently) free'd
==21270==
==21270==
==21270== Process terminating with default action of signal 11 (SIGSEGV): dumping core
==21270== Access not within mapped region at address 0x0
==21270== at 0x4D8185: pyuw_this_id(frame_info*, void**, frame_id*) (py-unwind.c:461)
==21270== by 0x6D426A: compute_frame_id(frame_info*) (frame.c:505)
==21270== by 0x6D43B7: get_frame_id(frame_info*) (frame.c:537)
==21270== by 0x84F3B8: scoped_restore_current_thread::scoped_restore_current_thread() (thread.c:1678)
==21270== by 0x718E3D: fetch_inferior_event(void*) (infrun.c:4076)
==21270== by 0x7067C9: inferior_event_handler(inferior_event_type, void*) (inf-loop.c:43)
==21270== by 0x45BEF9: handle_target_event(int, void*) (linux-nat.c:4419)
==21270== by 0x6C4255: handle_file_event(file_handler*, int) (event-loop.c:733)
==21270== by 0x6C47F8: gdb_wait_for_event(int) (event-loop.c:859)
==21270== by 0x6C3666: gdb_do_one_event() (event-loop.c:322)
==21270== by 0x6C3712: start_event_loop() (event-loop.c:371)
==21270== by 0x746801: captured_command_loop() (main.c:329)
==21270== If you believe this happened as a result of a stack
==21270== overflow in your program's main thread (unlikely but
==21270== possible), you can try to increase the size of the
==21270== main thread stack using the --main-stacksize= flag.
==21270== The main thread stack size used in this run was 8388608.
==21270==
Above, when we get to compute_frame_id, fi->unwind is non-NULL,
meaning, we found an unwinder, in this case the Python unwinder, but
somehow, fi->prologue_cache is left NULL. pyuw_this_id then crashes
because it assumes fi->prologue_cache is non-NULL:
static void
pyuw_this_id (struct frame_info *this_frame, void **cache_ptr,
struct frame_id *this_id)
{
*this_id = ((cached_frame_info *) *cache_ptr)->frame_id;
^^^^^^^^^^
'*cache_ptr' here is 'fi->prologue_cache'.
There's a quit() call in pyuw_sniffer that I believe is the one that
sometimes triggers the crash above. The crash can be reproduced
easily with this hack to force a quit out of the python unwinder:
--- a/gdb/python/py-unwind.c
+++ b/gdb/python/py-unwind.c
@@ -497,6 +497,8 @@ pyuw_sniffer (const struct frame_unwind *self, struct frame_info *this_frame,
struct gdbarch *gdbarch = (struct gdbarch *) (self->unwind_data);
cached_frame_info *cached_frame;
+ quit ();
+
gdbpy_enter enter_py (gdbarch, current_language);
TRACE_PY_UNWIND (3, "%s (SP=%s, PC=%s)\n", __FUNCTION__,
After that quit is thrown, any subsequent operation that involves
unwinding results in GDB crashing with SIGSEGV like above.
The problem is that this commit:
commit
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|---|---|---|
| bfd | ||
| binutils | ||
| config | ||
| cpu | ||
| elfcpp | ||
| etc | ||
| gas | ||
| gdb | ||
| gold | ||
| gprof | ||
| include | ||
| intl | ||
| ld | ||
| libdecnumber | ||
| libiberty | ||
| opcodes | ||
| readline | ||
| sim | ||
| texinfo | ||
| zlib | ||
| .cvsignore | ||
| .gitattributes | ||
| .gitignore | ||
| ChangeLog | ||
| compile | ||
| config-ml.in | ||
| config.guess | ||
| config.rpath | ||
| config.sub | ||
| configure | ||
| configure.ac | ||
| COPYING | ||
| COPYING3 | ||
| COPYING3.LIB | ||
| COPYING.LIB | ||
| COPYING.LIBGLOSS | ||
| COPYING.NEWLIB | ||
| depcomp | ||
| djunpack.bat | ||
| install-sh | ||
| libtool.m4 | ||
| lt~obsolete.m4 | ||
| ltgcc.m4 | ||
| ltmain.sh | ||
| ltoptions.m4 | ||
| ltsugar.m4 | ||
| ltversion.m4 | ||
| MAINTAINERS | ||
| Makefile.def | ||
| Makefile.in | ||
| Makefile.tpl | ||
| makefile.vms | ||
| missing | ||
| mkdep | ||
| mkinstalldirs | ||
| move-if-change | ||
| README | ||
| README-maintainer-mode | ||
| setup.com | ||
| src-release.sh | ||
| symlink-tree | ||
| ylwrap | ||
README for GNU development tools This directory contains various GNU compilers, assemblers, linkers, debuggers, etc., plus their support routines, definitions, and documentation. If you are receiving this as part of a GDB release, see the file gdb/README. If with a binutils release, see binutils/README; if with a libg++ release, see libg++/README, etc. That'll give you info about this package -- supported targets, how to use it, how to report bugs, etc. It is now possible to automatically configure and build a variety of tools with one command. To build all of the tools contained herein, run the ``configure'' script here, e.g.: ./configure make To install them (by default in /usr/local/bin, /usr/local/lib, etc), then do: make install (If the configure script can't determine your type of computer, give it the name as an argument, for instance ``./configure sun4''. You can use the script ``config.sub'' to test whether a name is recognized; if it is, config.sub translates it to a triplet specifying CPU, vendor, and OS.) If you have more than one compiler on your system, it is often best to explicitly set CC in the environment before running configure, and to also set CC when running make. For example (assuming sh/bash/ksh): CC=gcc ./configure make A similar example using csh: setenv CC gcc ./configure make Much of the code and documentation enclosed is copyright by the Free Software Foundation, Inc. See the file COPYING or COPYING.LIB in the various directories, for a description of the GNU General Public License terms under which you can copy the files. REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info on where and how to report problems.