linux-kernel - Re: [tip:x86/core 1/1] vmlinux.o: warning: objtool: rcar_pcie

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Message-ID: <20251013185011.GA2734756@noisy.programming.kicks-ass.net>
Date: Mon, 13 Oct 2025 20:50:11 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Ingo Molnar <mingo@...nel.org>, Kees Cook <kees@...nel.org>,
	kernel test robot <lkp@...el.com>
Subject: Re: [tip:x86/core 1/1] vmlinux.o: warning: objtool:
 rcar_pcie_probe+0x13e: no-cfi indirect call!

On Mon, Oct 13, 2025 at 11:30:59AM -0700, Nathan Chancellor wrote:

> Is there any way for objtool to detect these instances and emit a
> slightly differently worded message? Figured it was worth asking ;)

Objtool doesn't really do value tracking, but I'll see if I can hack
something together.

That is, as long as its always:

  xor %r11, %r11
  cs call __x86_indirect_thunk_r11

without any instructions in between, it should be relatively straight
forward. But the moment there can be anything in between we need to
track the value of r11 back from the call or something.