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According to the SystemTap documentation on user-space probes[0], stap probe points without semaphores are denoted by setting the semaphore address in the probe's note to zero. At present the code does do a comparison of the semaphore address against zero, but only after it's been relocated; as such it will (almost?) always fail, commonly resulting in GDB trying to overwrite the ELF magic located at the image's base address. This commit tests the address as specified in the SDT note rather than the relocated value in order to correctly detect absent probe semaphores. [0]: https://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation gdb/Changelog: 2020-01-11 George Barrett <bob@bob131.so> * stap-probe.c (stap_modify_semaphore): Don't check for null semaphores. (stap_probe::set_semaphore, stap_probe::clear_semaphore): Check for null semaphores. gdb/testsuite/ChangeLog: 2020-01-11 George Barrett <bob@bob131.so> * gdb.base/stap-probe.c (relocation_marker): Add dummy variable to help in finding the image relocation offset. * gdb.base/stap-probe.exp (stap_test): Accept arbitrary compile options in arguments. (stap_test_no_debuginfo): Likewise. (stap-probe-nosem-noopt-pie, stap-probe-nosem-noopt-nopie): Add test variants. (stap_test): Add null semaphore relocation test.
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.