Re: [PATCH v1 0/6] objtool: Fixup alternate feature relative addresses

[Peter Zijlstra <peterz@infradead.org>]

On Tue, May 05, 2026 at 02:16:22PM +0530, Sathvika Vasireddy wrote:
> This patch series implements build-time fixup of alternate feature
> relative addresses for powerpc.
> 
> Previously, Nicholas Piggin proposed a build-time solution using a
> custom PowerPC tool [1], which provided the foundation for this approach.
> The current implementation leverages objtool's existing ELF parsing
> infrastructure to do the same.
> 
> This patchset applies atop powerpc/merge branch.
> 
> [1] Original PowerPC tool approach:
>     http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20170521010130.13552-1-npiggin@gmail.com/
> 
> Testing:
> Build and Boot tested on ppc64le, ppc64be, and ppc32be configs.
> 
> Sathvika Vasireddy (6):
>   objtool/powerpc: Add build-time fixup of alternate feature branch
>     targets
>   objtool: Set ELF_F_LAYOUT flag to preserve vmlinux segment layout
>   objtool: Fix "can't find starting instruction" warnings on vmlinux
>   objtool/powerpc: Skip jump destination analysis and unnanotated
>     intra-function call warnings for --ftr-fixup
>   kbuild: Add objtool integration for PowerPC feature fixups
>   powerpc: Enable build-time feature fixup processing by default

Ooh, so 2/3 are because you're not running objtool on vmlinux.o, but
you're running it later in the link stage?

AFAICT ELF_F_LAYOUT should not hurt the normal objtool run, but it
shouldn't be needed either, because we run much earlier, before sections
are placed.

And that also explains why you're the first to have trouble with 'can't
find starting instruction'. vmlinux.o will have unplaced sections that
are all relative 0.

Hmm... perhaps this ftr fixup should be its own command, like klp. Not
munged into check thing. Josh?