On Wed, Jun 09, 2021 at 01:24:18PM +0200, Arnd Bergmann wrote: > On Wed, Jun 9, 2021 at 1:05 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote: > > On Thu, Feb 04, 2021 at 04:29:47PM +0100, Arnd Bergmann wrote: > > > From: Arnd Bergmann <arnd@xxxxxxxx> > > > > > > ARM randconfig builds with lld sometimes show a build failure > > > from kallsyms: > > > > > > Inconsistent kallsyms data > > > Try make KALLSYMS_EXTRA_PASS=1 as a workaround > > > > > > The problem is the veneers/thunks getting added by the linker extend > > > the symbol table, which in turn leads to more veneers being needed, > > > so it may take a few extra iterations to converge. > > > > > > This bug has been fixed multiple times before, but comes back every time > > > a new symbol name is used. lld uses a different set of idenitifiers from > > > ld.bfd, so the additional ones need to be added as well. > > > > > > I looked through the sources and found that arm64 and mips define similar > > > prefixes, so I'm adding those as well, aside from the ones I observed. I'm > > > not sure about powerpc64, which seems to already be handled through a > > > section match, but if it comes back, the "__long_branch_" and "__plt_" > > > prefixes would have to get added as well. > > > > > > > This is such a whack-a-mole. The problem is hitting us yet again. I suspect > > it may be due to a new version of lld using new symbols, but I didn't really > > try to track it down. Is there an easy way to search for missed symbols ? > > The way I did it previously was to hack Kbuild to not remove the temporary > files after a failure, and then compare the "objdump --syms" output of the > last two stages. Problem with that is that we have a non-deterministic problem: The build fails for us on some build servers, but we are unable to reproduce the problem when building the same image manually on a development server. That is similar to what I had observed before, where powerpc builds would pass on one server, but the same kernel with the same configuration would fail to build on a second almost identical server. It would really be great if we can find a better solution. > > I suppose we could improve the situation if scripts/link-vmlinux.sh was able > to do that automatically, and compare the kallsyms output .S file between > steps 1 and 2. Comparing the .S files doesn't result in useful data; turns out there are always irrelevant differences. We'll try to run a diff on the output of "objdump --syms". Hopefully that will generate something useful. Thanks, Guenter
