Comment 4 for bug 2019160

Hi,

In Ubuntu we use -fdebug-prefix-map to remap a package's build directory (which contains random stuff) into a predictable path under /usr/src. This is done in order to help debuginfod index the source code for our packages.

Things work very well, but I found a weird corner case involving LTO. The affected package is vim. You can see the build logs for it here:

https://launchpadlibrarian.net/665520301/buildlog_ubuntu-mantic-amd64.vim_2%3A9.0.1378-2ubuntu1_BUILDING.txt.gz

As you can notice, we're using -fdebug-prefix-map and LTO for the build.

The problem is that the resulting debuginfo doesn't have the remaped directory. I can replicate the issue locally, and at first I thought this was either bug #108464 or #87726, but after some digging I'm convinced it's something else. I've compiled gcc (GCC) 14.0.0 20230510 from the master branch (608e7f3ab47fe746279c552c3574147aa3d8ee76), and I still can reproduce the problem.

A simple reproducer for the problem follows:

$ echo 'int main(){}' > foo.c $ ~/gcc/install/bin/gcc -c foo.c -O2 -g -flto=auto -ffat-lto-objects -fdebug-prefix-map=`pwd`=/aaaaaaa -o foo $ ~/gcc/install/bin/gcc foo -flto=auto -ffat-lto-objects -o bar

A workaround for this bug is to either stop using LTO or explicitly set -fdebug-prefix-map when linking the object.