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Andrew Burgess aff250145a gdb: generate gdb-index identically regardless of work thread count
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>
2023-11-28 10:23:19 +00:00
bfd Automatic date update in version.in 2023-11-28 00:00:24 +00:00
binutils Restore .gdb_index v9 display in readelf 2023-11-20 09:31:32 -07:00
config
contrib
cpu
elfcpp
etc
gas testsuite: Clean up .allow_index_reg in i386 tests 2023-11-28 13:29:01 +08:00
gdb gdb: generate gdb-index identically regardless of work thread count 2023-11-28 10:23:19 +00:00
gdbserver Introduce throw_winerror_with_name 2023-11-27 12:55:14 -07:00
gdbsupport [gdb] Fix segfault in for_each_block, part 1 2023-11-28 10:31:25 +01:00
gnulib
gold
gprof
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include RISC-V: reduce redundancy in sign/zero extension macro insn handling 2023-11-24 09:53:55 +01:00
ld New Romanian translation for ld 2023-11-28 10:16:36 +00:00
libbacktrace
libctf libctf: adding CU mappings should be idempotent 2023-11-20 12:31:41 +00:00
libdecnumber
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opcodes as: Add new estimated reciprocal instructions in LoongArch v1.1 2023-11-27 15:18:15 +08:00
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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
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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.