[PATCH] D54125: [LTO] Drop non-prevailing definitions only if linkage is not local or appending

[Teresa Johnson via Phabricator via llvm-commits]

tejohnson added a comment.

In D54125#1314634 <https://reviews.llvm.org/D54125#1314634>, @tejohnson wrote:

> In D54125#1313868 <https://reviews.llvm.org/D54125#1313868>, @void wrote:
>
> > To replicate the failure, do this:
> >
> >   $ llvm-ar rcsTD test-archive.o softirq.o irqdesc.o
> >   $ ld.gold -plugin LLVMgold.so -plugin-opt=thinlto -plugin-opt=-code-model=kernel -plugin-opt=jobs=6 -plugin-opt=-stack-alignment=8 -m elf_x86_64 -r -o test-object.o --whole-archive test-archive.o
> >   $ nm test-object.o  | grep W
> >   0000000000001370 W arch_dynirq_lower_bound
> >   00000000000001b0 W arch_early_irq_init
> >   00000000000001a0 W arch_probe_nr_irqs
> >   0000000000000190 W early_irq_init
> >
> >
> > Note that `early_irq_init` is still weak. It should have resolved to a concrete function.
>
>
> I tried the reproducer and via -plugin-opts=save-temps I can see that the linker is telling LTO that the copy of early_irq_init in irqdesc.o is non-prevailing and that the softirq.o copy is prevailing. Therefore, with this patch the copy in irqdesc.o which is non-weak is dropped, and the weak copy in softirq.o is kept. So LTO seems to be doing what it should be based on what gold tells it.
>
> The question is why is gold picking the weak symbol as the prevailing copy and not the strong one? Note that if the order of the object files is reversed in the llvm-ar invocation, the irqdesc.o copy of that symbol is the prevailing one as per the linker, and we keep the strong symbol instead.


Interestingly, lld behaves differently. Even with the softirq.o being put first in the archive as you have in your repro, it says that the version of early_irq_init in irqdesc is the prevailing copy, and the strong symbol is kept. Bug in gold?


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