linux-kernel - [tip:x86/urgent] x86/vdso: Fix the build on GCC5

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Message-ID: <tip-e893286918d2cde3a94850d8f7101cd1039e0c62@git.kernel.org>
Date:	Fri, 6 Mar 2015 00:39:38 -0800
From:	tip-bot for Jiri Slaby <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	luto@...capital.net, linux-kernel@...r.kernel.org, jslaby@...e.cz,
	stable@...r.kernel.org, torvalds@...ux-foundation.org,
	bp@...en8.de, mingo@...nel.org, rguenther@...e.de, hpa@...or.com,
	tglx@...utronix.de
Subject: [tip:x86/urgent] x86/vdso: Fix the build on GCC5

Commit-ID:  e893286918d2cde3a94850d8f7101cd1039e0c62
Gitweb:     http://git.kernel.org/tip/e893286918d2cde3a94850d8f7101cd1039e0c62
Author:     Jiri Slaby <jslaby@...e.cz>
AuthorDate: Thu, 5 Mar 2015 09:13:31 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 6 Mar 2015 09:34:45 +0100

x86/vdso: Fix the build on GCC5

On gcc5 the kernel does not link:

  ld: .eh_frame_hdr table[4] FDE at 0000000000000648 overlaps table[5] FDE at 0000000000000670.

Because prior GCC versions always emitted NOPs on ALIGN directives, but
gcc5 started omitting them.

.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 69d0627a7f6e ("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".

So fix this by adding to that point at least a single NOP and make the
function ALIGN possibly with more NOPs then.

Kudos for reporting and diagnosing should go to Richard.

Reported-by: Richard Biener <rguenther@...e.de>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
Acked-by: Andy Lutomirski <luto@...capital.net>
Cc: <stable@...r.kernel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/1425543211-12542-1-git-send-email-jslaby@suse.cz
Signed-off-by: Ingo Molnar <mingo@...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 31776d0..d7ec4e2 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:
--
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