linux-kernel - Re: [PATCH] objtool: Detect non-relocated text references

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Message-ID: <20241004072847.zihm6dw7y5m4e2lb@treble>
Date: Fri, 4 Oct 2024 00:28:47 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] objtool: Detect non-relocated text references

On Fri, Oct 04, 2024 at 08:54:16AM +0200, Ard Biesheuvel wrote:
> On Fri, 4 Oct 2024 at 02:31, Josh Poimboeuf <jpoimboe@...nel.org> wrote:
> > However there are some "lea xxx(%rip)" cases which don't use relocations
> > because they're referencing code in the same translation unit.
> 
> input section

"in the same translation unit and section" ?

> > However if we enable -fpie, the compiler would start generating them and
> > there would definitely be bugs in the IBT sealing.
> >
> 
> -fpie is guaranteed to break things, but even without it, Clang may
> issue RIP-relative LEA instructions (or LLD when it performs
> relaxations), so this is definitely worth addressing even if we don't
> enable -fpie.

I haven't seen this with Clang either.  Also, objtool runs before the
linker so LLD relaxations shouldn't matter.

-- 
Josh