linux-kernel - Re: [FYI] objtool: .export_symbol…: data relocation to !ENDBR: stpcpy

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Message-ID: <20240802093552.GG39708@noisy.programming.kicks-ass.net>
Date: Fri, 2 Aug 2024 11:35:52 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [FYI] objtool: .export_symbol…:
 data relocation to !ENDBR: stpcpy

On Thu, Aug 01, 2024 at 05:28:36PM +0200, Sebastian Andrzej Siewior wrote:
> Hi,
> 
> defconfig on x86-64 with gcc-14 I get this:
> | vmlinux.o: warning: objtool: .export_symbol+0x26980: data relocation to !ENDBR: stpcpy+0x0
> 
> objdump ->
> 
> | 0000000000000110 <stpcpy>:
> |  110:   66 66 2e 0f 1f 84 00    data16 cs nopw 0x0(%rax,%rax,1)
> |  117:   00 00 00 00 
> |  11b:   0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)
> |  120:   f3 0f 1e fa             endbr64
> 
> okay, no endbr64 on entry label.
> 
> | $ make lib/string.s
> ->
> |         .type   stpcpy, @function
> | stpcpy:
> |         .p2align 5
> |         endbr64
> | .L30:
> | # lib/string.c:193:  while ((*dest++ = *src++) != '\0')
> |         movzbl  (%rsi), %eax    # MEM[(const char *)src_8 + -1B], _1
> 
> an alignment request after the function label before endbr64 which gets
> expanded into NOP_11+NOP_5.
> I don't see this with gcc-13.
> Reported as https://gcc.gnu.org/PR116174

Fun, thanks for tracking that down!