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It was observed that changing the number of worker threads that GDB uses (maintenance set worker-threads NUM) would have an impact on the layout of the generated gdb-index. The cause seems to be how the CU are distributed between threads, and then symbols that appear in multiple CU can be encountered earlier or later depending on whether a particular CU moves between threads. I certainly found this behaviour was reproducible when generating an index for GDB itself, like: gdb -q -nx -nh -batch \ -eiex 'maint set worker-threads NUM' \ -ex 'save gdb-index /tmp/' And then setting different values for NUM will change the generated index. Now, the question is: does this matter? I would like to suggest that yes, this does matter. At Red Hat we generate a gdb-index as part of the build process, and we would ideally like to have reproducible builds: for the same source, compiled with the same tool-chain, we should get the exact same output binary. And we do .... except for the index. Now we could simply force GDB to only use a single worker thread when we build the index, but, I don't think the idea of reproducible builds is that strange, so I think we should ensure that our generated indexes are always reproducible. To achieve this, I propose that we add an extra step when building the gdb-index file. After constructing the initial symbol hash table contents, we will pull all the symbols out of the hash, sort them, then re-insert them in sorted order. This will ensure that the structure of the generated hash will remain consistent (given the same set of symbols). I've extended the existing index-file test to check that the generated index doesn't change if we adjust the number of worker threads used. Given that this test is already rather slow, I've only made one change to the worker-thread count. Maybe this test should be changed to use a smaller binary, which is quicker to load, and for which we could then try many different worker thread counts. Approved-By: Tom Tromey <tom@tromey.com> |
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bfd | ||
binutils | ||
config | ||
contrib | ||
cpu | ||
elfcpp | ||
etc | ||
gas | ||
gdb | ||
gdbserver | ||
gdbsupport | ||
gnulib | ||
gold | ||
gprof | ||
gprofng | ||
include | ||
ld | ||
libbacktrace | ||
libctf | ||
libdecnumber | ||
libiberty | ||
libsframe | ||
opcodes | ||
readline | ||
sim | ||
texinfo | ||
zlib | ||
.cvsignore | ||
.editorconfig | ||
.gitattributes | ||
.gitignore | ||
ar-lib | ||
ChangeLog | ||
compile | ||
config-ml.in | ||
config.guess | ||
config.rpath | ||
config.sub | ||
configure | ||
configure.ac | ||
COPYING | ||
COPYING3 | ||
COPYING3.LIB | ||
COPYING.LIB | ||
COPYING.LIBGLOSS | ||
COPYING.NEWLIB | ||
depcomp | ||
djunpack.bat | ||
install-sh | ||
libtool.m4 | ||
lt~obsolete.m4 | ||
ltgcc.m4 | ||
ltmain.sh | ||
ltoptions.m4 | ||
ltsugar.m4 | ||
ltversion.m4 | ||
MAINTAINERS | ||
Makefile.def | ||
Makefile.in | ||
Makefile.tpl | ||
makefile.vms | ||
missing | ||
mkdep | ||
mkinstalldirs | ||
move-if-change | ||
multilib.am | ||
README | ||
README-maintainer-mode | ||
SECURITY.txt | ||
setup.com | ||
src-release.sh | ||
symlink-tree | ||
test-driver | ||
ylwrap |
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.