linux-kernel - Re: objtool crash processing drivers/gpu/drm/vmwgfx/vmwgfx

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Message-ID: <grnfthlwv6jozl4psujzqyj7mwnsyugpwr5tcy72n4qermqpyp@mabr2g2dbt2g>
Date: Thu, 27 Mar 2025 20:57:49 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Ingo Molnar <mingo@...nel.org>
Cc: Arnd Bergmann <arnd@...db.de>, Peter Zijlstra <peterz@...radead.org>, 
	linux-kernel@...r.kernel.org
Subject: Re: objtool crash processing drivers/gpu/drm/vmwgfx/vmwgfx_msg.o

On Thu, Mar 27, 2025 at 05:41:18PM +0100, Ingo Molnar wrote:
> 
> * Arnd Bergmann <arnd@...db.de> wrote:
> 
> > I saw this on one randconfig build failing today with yesterday's
> > next-20250326 (with a couple of patches on top), using gcc-14.2
> > and the attached config I assume this is a rare configuration:
> > 
> > ./tools/objtool/objtool --hacks=jump_label --hacks=noinstr --sls --stackval --static-call --uaccess   --module drivers/gpu/drm/vmwgfx/vmwgfx_msg.o
> > Segmentation fault
> > 
> > I have not tried to analyze it any further, but I would guess that
> > this is a rare configuration, not a recent regression.
> 
> I can reproduce this now too, not with a randconfig but with a distro 
> DEB package build:

Thanks, I was able to reproduce with both configs.  The below fixes it,
which then results in another warning:

  drivers/gpu/drm/vmwgfx/vmwgfx_msg.o: warning: objtool: vmw_recv_msg.cold+0x0: unreachable instruction
  drivers/gpu/drm/vmwgfx/vmwgfx_msg.o: warning: objtool: vmw_recv_msg.cold+0x3: unreachable instruction
  drivers/gpu/drm/vmwgfx/vmwgfx_msg.o: warning: objtool: vmw_recv_msg.cold+0x6: skipping duplicate warning(s)

Which is another easy fix.  I'll send patches.

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 3bf29923d5c0..29de1709ea00 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -4037,7 +4037,7 @@ static bool ignore_unreachable_insn(struct objtool_file *file, struct instructio
 	 * It may also insert a UD2 after calling a __noreturn function.
 	 */
 	prev_insn = prev_insn_same_sec(file, insn);
-	if (prev_insn->dead_end &&
+	if (prev_insn && prev_insn->dead_end &&
 	    (insn->type == INSN_BUG ||
 	     (insn->type == INSN_JUMP_UNCONDITIONAL &&
 	      insn->jump_dest && insn->jump_dest->type == INSN_BUG)))