On Wed, Mar 24, 2021 at 10:45:36PM +0000, Sean Christopherson wrote: > On Tue, Mar 23, 2021, Sami Tolvanen wrote: > > On Tue, Mar 23, 2021 at 9:36 AM Sean Christopherson <[email protected]> > > wrote: > > > > > > On Tue, Mar 23, 2021, Sami Tolvanen wrote: > > > > On Mon, Mar 22, 2021 at 4:44 PM Sean Christopherson <[email protected]> > > > > wrote: > > > > > > > > > > Merge module sections only when using Clang LTO. With gcc-10, merging > > > > > sections does not appear to update the symbol tables for the module, > > > > > e.g. 'readelf -s' shows the value that a symbol would have had, if > > > > > sections were not merged. > > > > > > > > I'm fine with limiting this to LTO only, but it would be helpful to > > > > understand which sections are actually getting merged here. > > > > > > It doesn't appear to matter which sections get merged, the tables only > > > show the > > > correct data if there is no merging whatsoever, e.g. allowing merging for > > > any > > > one of the four types (.bss, .data, .rodata and .text) results in > > > breakage. > > > AFAICT, merging any sections causes the layout to change and throw off the > > > symbol tables. > > > > Thanks for the clarification. I can reproduce this issue with gcc + > > bfd if any of the sections are merged, but gcc + lld produces valid > > symbol tables. > > FWIW, clang + bfd also produces mangled tables, so it does appear to be bfd > specific.
Are you able to open a bug against bfd for this? > > Perhaps someone more familiar with bfd can comment on whether this is > > a bug or a feature, and if there's a flag we can pass to bfd that > > would fix the issue. In the meanwhile, this patch looks like a > > reasonable workaround to me. > > > > Reviewed-by: Sami Tolvanen <[email protected]> > > Tested-by: Sami Tolvanen <[email protected]> Thanks, I'll get this sent to Linus. -- Kees Cook
