Re: [PATCH v2 3/6] objtool: Fix "can't find starting instruction" warnings on vmlinux
flat view
From: Peter Zijlstra <peterz@infradead.org>
Date: 2026-09-29 14:24:51
Also in:
linux-kbuild, lkml
On Tue, Sep 29, 2026 at 11:21:34AM +0530, Shivang Upadhyay wrote:
From: Sathvika Vasireddy <redacted> 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?
quoted hunk ↗ jump to hunk
+ 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?