https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101473
--- Comment #17 from tonyb at cybernetics dot com --- (In reply to Richard Biener from comment #16) > I'm interested if remaining differences are due to the same underlying issue > or not I tested your updated patch with gcc 10.2 (I had to make a small change due to the definition of struct dwarf_file_data being in dwarf2out.c rather than dwarf2out.h in gcc 10.2). I got the same results as before, with the same list of files being non-reproducible. I decided to debug the problem with pciutils. For pciutils, the problem was caused by the following: Yocto CFLAGS contains -ffile-prefix-map but LDFLAGS doesn't. The pciutils Makefile compiles *.c files to *.o files with CFLAGS and links them with LDFLAGS but not CFLAGS. With LTO disabled, this results in a reproducible binary, but with LTO enabled, this results in a non-reproducible binary. So I can workaround by adding -ffile-prefix-map to LDFLAGS. So is this considered a bug? If the prefix map translation can be handled completely before generating the *.o file, then it could be fixed in gcc, but I am not sure how it all works. One solution that is apparently off the table is embedding the prefix map in the *.o file, since that would make the *.o file non-reproducible (see e.g. bug 68848; apparently the prefix map used to be present in the *.o file but was removed in some recent version of gcc). If this issue is not considered a bug, then I will pass on to the Yocto people that they should use -ffile-prefix-map in LDFLAGS in addition to CFLAGS, and you can close this PR. I haven't looked into the other packages that were not reproducible, but I suspect the same issue. I will attach a test script that shows the issue if you want to debug it further.
