1e6205909c
The condition of a breakpoint can be set with the 'cond' command. If
the condition has errors that make it problematic to evaluate, it
appears like GDB rejects the condition, but updates the breakpoint's
condition string, which causes incorrect/unintuitive behavior.
For instance:
$ gdb ./test
Reading symbols from ./test...
(gdb) break 5
Breakpoint 1 at 0x1155: file test.c, line 5.
(gdb) cond 1 gibberish
No symbol "gibberish" in current context.
At this point, it looks like the condition was rejected.
But "info breakpoints" shows the following:
(gdb) info breakpoints
Num Type Disp Enb Address What
1 breakpoint keep y 0x0000000000001155 in main at test.c:5
stop only if gibberish
Running the code gives the following behavior, where re-insertion of
the breakpoint causes failures.
(gdb) run
Starting program: test
warning: failed to reevaluate condition for breakpoint 1: No symbol "gibberish" in current context.
warning: failed to reevaluate condition for breakpoint 1: No symbol "gibberish" in current context.
warning: failed to reevaluate condition for breakpoint 1: No symbol "gibberish" in current context.
warning: failed to reevaluate condition for breakpoint 1: No symbol "gibberish" in current context.
warning: failed to reevaluate condition for breakpoint 1: No symbol "gibberish" in current context.
[Inferior 1 (process 19084) exited normally]
(gdb)
This broken behavior occurs because GDB updates the condition string
of the breakpoint *before* checking that it parses successfully.
When parsing fails, the update has already taken place.
Fix the problem by updating the condition string *after* parsing the
condition. We get the following behavior when this patch is applied:
$ gdb ./test
Reading symbols from ./test...
(gdb) break 5
Breakpoint 1 at 0x1155: file test.c, line 5.
(gdb) cond 1 gibberish
No symbol "gibberish" in current context.
(gdb) info breakpoints
Num Type Disp Enb Address What
1 breakpoint keep y 0x0000000000001155 in main at test.c:5
(gdb) run
Starting program: test
Breakpoint 1, main () at test.c:5
5 a = a + 1; /* break-here */
(gdb) c
Continuing.
[Inferior 1 (process 15574) exited normally]
(gdb)
A side note: The problem does not occur if the condition is given
at the time of breakpoint definition, as in "break 5 if gibberish",
because the parsing of the condition fails during symtab-and-line
creation, before the breakpoint is created.
Finally, the code included the following comment:
/* I don't know if it matters whether this is the string the user
typed in or the decompiled expression. */
This comment did not make sense to me because the condition string is
the user-typed input. The patch updates this comment, too.
gdb/ChangeLog:
2020-07-30 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
* breakpoint.c (set_breakpoint_condition): Update the
condition string after parsing the new condition successfully.
gdb/testsuite/ChangeLog:
2020-07-30 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
* gdb.base/condbreak-bad.c: New test.
* gdb.base/condbreak-bad.exp: New file.
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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.