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From glibc 2.35 and later, the "map_failed" stap probe is no longer included in glibc. The removal of the probe looks like an accident, but it was caused by a glibc commit which meant that the "map_failed" probe could no longer be reached; the compiler then helpfully optimised out the probe. In GDB, in solib-svr4.c, we have a list of probes that we look for related to the shared library loading detection. If any of these probes are missing then GDB will fall back to the non-probe based mechanism for detecting shared library loading. The "map_failed" probe is include in the list of required probes. This means that on glibc 2.35 (or later) systems, GDB is going to always fall back to the non-probes based mechanism for detecting shared library loading. I raised a glibc bug to discuss this issue: https://sourceware.org/bugzilla/show_bug.cgi?id=29818 But, whatever the ultimate decision from the glibc team, given there are version of glibc in the wild without the "map_failed" probe, we probably should update GDB to handle this situation. The "map_failed" probe is already a little strange, very early versions of glibc didn't include this probe, so, in some cases, if this probe is missing GDB is happy to ignore it. This is fine, the action associated with this probe inside GDB is DO_NOTHING, this means the probe isn't actually required in order for GDB to correctly detect the loading of shared libraries. In this commit I propose changing the rules so that any probe whose action is DO_NOTHING, is optional. There is one possible downside to this change, and that concerns 'set stop-on-solib-events on'. If a probe is removed from glibc, but the old style breakpoint based mechanism is still in place within glibc for that same event, then GDB will stop when using the old style non-probe based mechanism, but not when using the probes based mechanism. For the map_failed case this is not a problem, both the map_failed probe, and the call to the old style breakpoint location were optimised out, and so neither event (probes based, or breakpoint based) will trigger. This would only become an issue if glibc removed a probe, but left the breakpoint in place (this would almost certainly be a bug in glibc). For now, I'm proposing that we just don't worry about this. Because some probes have actions that are not DO_NOTHING, then we know the user will always seem _some_ stops when a shared library is loaded/unloaded, and (I'm guessing), in most cases, that's all they care about. I figure when someone complains then we can figure out what the right solution is then. With this commit in place, then, when using a glibc 2.35 or later system, GDB will once again use the stap probes for shared library detection. Reviewed-By: Lancelot SIX <lancelot.six@amd.com>
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.