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b4b3e2dee2
Consider the following chain of events:
* GDB is performing an inferior call, and
* the inferior calls longjmp, and
* GDB detects that the longjmp has completed, stops, and enters
check_longjmp_breakpoint_for_call_dummy (in breakpoint.c), and
* GDB tries to unwind the stack in order to check that the dummy
frame (setup for the inferior call) is still on the stack, but
* The unwind fails, possibly due to missing debug information, so
* GDB incorrectly concludes that the inferior has longjmp'd past the
dummy frame, and so deletes the dummy frame, including the dummy
frame breakpoint, but then
* The inferior continues, and eventually returns to the dummy frame,
which is usually (always?) on the stack, the inferior starts
trying to execute the random contents of the stack, this results
in undefined behaviour.
This situation is already warned about in the comment on the function
check_longjmp_breakpoint_for_call_dummy where we say:
You should call this function only at places where it is safe to currently
unwind the whole stack. Failed stack unwind would discard live dummy
frames.
The warning here is fine, the problem is that, even though we call the
function from a location within GDB where we hope to be able to
unwind, sometime the state of the inferior means that the unwind will
not succeed.
This commit tries to improve the situation by adding the following
additional check; when GDB fails to find the dummy frame on the stack,
instead of just assuming that the dummy frame can be garbage
collected, first find the stop_reason for the last frame on the stack.
If this stop_reason indicates that the stack unwinding may have failed
then we assume that the dummy frame is still in use. However, if the
last frame's stop_reason indicates that the stack unwind completed
successfully then we can be confident that the dummy frame is no
longer in use, and we garbage collect it.
Tested on x86-64 GNU/Linux.
gdb/ChangeLog:
* breakpoint.c (check_longjmp_breakpoint_for_call_dummy): Add
check for why the backtrace stopped.
gdb/testsuite/ChangeLog:
* gdb.base/premature-dummy-frame-removal.c: New file.
* gdb.base/premature-dummy-frame-removal.exp: New file.
* gdb.base/premature-dummy-frame-removal.py: New file.
Change-Id: I8f330cfe0f3f33beb3a52a36994094c4abada07e
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.