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... as it's _much_ faster. Hacking the gdb.threads/attach-many-short-lived-threads.exp test to spawn thousands of threads instead of dozens to stress and debug timeout problems with gdb.threads/attach-many-short-lived-threads.exp, I saw that GDB would spend several seconds just reading the /proc/PID/smaps file, to determine the vDSO mapping range. GDB opens and reads the whole file just once, and caches the result, but even that is too slow. For example, with almost 8000 threads: $ ls /proc/3518/task/ | wc -l 7906 reading the /proc/PID/smaps file grepping for "vdso" takes over 15 seconds : $ time cat /proc/3518/smaps | grep vdso 7ffdbafee000-7ffdbaff0000 r-xp 00000000 00:00 0 [vdso] real 0m15.371s user 0m0.008s sys 0m15.017s Looking around the web for hints, I found a nice description of the issue here: http://backtrace.io/blog/blog/2014/11/12/large-thread-counts-and-slow-process-maps/ The problem is that /proc/PID/smaps wants to show the mappings as being thread stack, and that has the kernel iterating over all threads in the thread group, for each mapping. The fix is to use the "map" file under /proc/PID/task/PID/ instead of the /proc/PID/ one, as the former doesn't mark thread stacks for all threads. That alone drops the timing to the millisecond range on my machine: $ time cat /proc/3518/task/3518/smaps | grep vdso 7ffdbafee000-7ffdbaff0000 r-xp 00000000 00:00 0 [vdso] real 0m0.150s user 0m0.009s sys 0m0.084s And since we only need the vdso mapping's address range, we can use "maps" file instead of "smaps", and it's even cheaper: /proc/PID/task/PID/maps : $ time cat /proc/3518/task/3518/maps | grep vdso 7ffdbafee000-7ffdbaff0000 r-xp 00000000 00:00 0 [vdso] real 0m0.027s user 0m0.000s sys 0m0.017s gdb/ChangeLog: 2016-05-24 Pedro Alves <palves@redhat.com> PR gdb/19828 * linux-tdep.c (find_mapping_size): Delete. (linux_vsyscall_range_raw): Rewrite reading from /proc/PID/task/PID/maps directly instead of using gdbarch_find_memory_regions.
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.