Re: [PATCH v2 3/6] objtool: Fix "can't find starting instruction" warnings on vmlinux

[Peter Zijlstra <peterz@infradead.org>]

On Tue, Sep 29, 2026 at 11:21:34AM +0530, Shivang Upadhyay wrote:
> From: Sathvika Vasireddy <sv@linux.ibm.com>
> 
> Objtool throws a lot of can't find starting instruction warnings
> when run on vmlinux with --ftr-fixup option.
> 
> These warnings are seen because find_insn() function looks for
> instructions at offsets that are relative to the start of the section.
> In case of individual object files (.o), there are no can't find
> starting instruction warnings seen because the actual offset
> associated with an instruction is itself a relative offset since the
> sections start at offset 0x0.
> 
> However, in case of vmlinux, find_insn() function fails to find
> instructions at the actual offset associated with an instruction
> since the sections in vmlinux do not start at offset 0x0. Due to
> this, find_insn() will look for absolute offset and not the relative
> offset. This is resulting in a lot of can't find starting instruction
> warnings when objtool is run on vmlinux.

I'm confused; decode_instructions() iterates the section and inserts the
instructions at the exact offset it finds them at. Therefore it should
be able to find them again at that same offset, irrespective of the
actual start, no?

> +			if (func->len == 0 && is_notype_sym(func))
> +				continue;
> +
> +			func_off = opts.ftr_fixup ?
> +				func->offset - sec->sh.sh_addr : func->offset;

function offset really should not depend on opts. It should work
irrespective of any option, no?