linux-kernel - [PATCH 1/1] x86/vdso: fix a reference to a non-existing instruction

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Date:	Thu,  5 Mar 2015 09:13:31 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	luto@...capital.net
Cc:	linux-kernel@...r.kernel.org, rguenther@...e.de,
	Jiri Slaby <jslaby@...e.cz>, stable@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: [PATCH 1/1] x86/vdso: fix a reference to a non-existing instruction

.LSTARTFDEDLSI1 says:
        /* HACK: The dwarf2 unwind routines will subtract 1 from the
           return address to get an address in the middle of the
           presumed call instruction.  Since we didn't get here via
           a call, we need to include the nop before the real start
           to make up for it.  */
        .long .LSTART_sigreturn-1-.     /* PC-relative start address */

But commit 69d0627a7f6e891189124d784d2fa90cae7c449a (x86 vDSO: reorder
vdso32 code) from 2.6.25 replaced
  .org __kernel_vsyscall+32,0x90
by ALIGN right before __kernel_sigreturn. Of course, ALIGN need not
generate any nop in there. Esp. gcc5 collapses vclock_gettime.o and
int80.o together with no generated nops as "ALIGN". In that case
kernel does not even link:
ld: .eh_frame_hdr table[4] FDE at 0000000000000648 overlaps table[5] FDE at 0000000000000670.

So fix this by adding there at least a single nop and make the
function ALIGN possibly with more nops then.

Kudos for reporting and diagnosing should go to Richard.

Signed-off-by: Jiri Slaby <jslaby@...e.cz>
Reported-by: Richard Biener <rguenther@...e.de>
Cc: stable@...r.kernel.org
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: x86@...nel.org
---
 arch/x86/vdso/vdso32/sigreturn.S | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/vdso/vdso32/sigreturn.S b/arch/x86/vdso/vdso32/sigreturn.S
index 31776d0efc8c..d7ec4e251c0a 100644
--- a/arch/x86/vdso/vdso32/sigreturn.S
+++ b/arch/x86/vdso/vdso32/sigreturn.S
@@ -17,6 +17,7 @@
 	.text
 	.globl __kernel_sigreturn
 	.type __kernel_sigreturn,@function
+	nop /* this guy is needed for .LSTARTFDEDLSI1 below (watch for HACK) */
 	ALIGN
 __kernel_sigreturn:
 .LSTART_sigreturn:
-- 
2.3.0

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