linux-kernel - Re: linux-next: Tree for Apr 3 (objtool)

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Date:   Wed, 3 Apr 2019 15:53:05 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: linux-next: Tree for Apr 3 (objtool)

On Wed, Apr 03, 2019 at 08:02:43AM -0700, Randy Dunlap wrote:
> On 4/3/19 1:24 AM, Stephen Rothwell wrote:
> > Hi all,
> > 
> > Changes since 20190402:
> > 
> 
> on x86_64:
> 
> arch/x86/entry/entry_64.o: warning: objtool: .entry.text+0x909: unreachable instruction

Your .o file looks odd.  I can't recreate the issue when I build the
same object.

Did the issue only just now show up?  Can you bisect it?  What version
of binutils are you using?

Here's the disassembly:

------------------
     903:	e8 00 00 00 00       	callq  908 <interrupt_entry+0xc8>
			904: R_X86_64_PC32	trace_hardirqs_off_thunk-0x4
     908:	c3                   	retq   
     909:	eb 75                	jmp    980 <common_interrupt>
     90b:	66 66 2e 0f 1f 84 00 	data16 nopw %cs:0x0(%rax,%rax,1)
     912:	00 00 00 00 
     916:	66 66 2e 0f 1f 84 00 	data16 nopw %cs:0x0(%rax,%rax,1)
     91d:	00 00 00 00 
     921:	66 66 2e 0f 1f 84 00 	data16 nopw %cs:0x0(%rax,%rax,1)
     928:	00 00 00 00 
     92c:	66 66 2e 0f 1f 84 00 	data16 nopw %cs:0x0(%rax,%rax,1)
     933:	00 00 00 00 
     937:	66 66 2e 0f 1f 84 00 	data16 nopw %cs:0x0(%rax,%rax,1)
     93e:	00 00 00 00 
     942:	66 66 2e 0f 1f 84 00 	data16 nopw %cs:0x0(%rax,%rax,1)
     949:	00 00 00 00 
     94d:	66 66 2e 0f 1f 84 00 	data16 nopw %cs:0x0(%rax,%rax,1)
     954:	00 00 00 00 
     958:	66 66 2e 0f 1f 84 00 	data16 nopw %cs:0x0(%rax,%rax,1)
     95f:	00 00 00 00 
     963:	66 66 2e 0f 1f 84 00 	data16 nopw %cs:0x0(%rax,%rax,1)
     96a:	00 00 00 00 
     96e:	66 66 2e 0f 1f 84 00 	data16 nopw %cs:0x0(%rax,%rax,1)
     975:	00 00 00 00 
     979:	0f 1f 80 00 00 00 00 	nopl   0x0(%rax)

0000000000000980 <common_interrupt>:
------------------

Where the heck does that "jmp 980" come from?  I don't see it in the
code:

------------------
ENTRY(interrupt_entry)
	....
	TRACE_IRQS_OFF

	ret
END(interrupt_entry)
_ASM_NOKPROBE(interrupt_entry)


/* Interrupt entry/exit. */

	/*
	 * The interrupt stubs push (~vector+0x80) onto the stack and
	 * then jump to common_interrupt.
	 */
	.p2align CONFIG_X86_L1_CACHE_SHIFT
common_interrupt:
------------------

Hopefully gas isn't inserting stray jumps for code alignments...

-- 
Josh