[PATCH 3.4 102/172] x86/vdso: Fix the build on GCC5

From: lizf
Date: Tue Jun 16 2015 - 05:14:22 EST

From: Jiri Slaby <jslaby@xxxxxxx>

3.4.108-rc1 review patch. If anyone has any objections, please let me know.


commit e893286918d2cde3a94850d8f7101cd1039e0c62 upstream.

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.


/* 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

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@xxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
Acked-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1425543211-12542-1-git-send-email-jslaby@xxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Zefan Li <lizefan@xxxxxxxxxx>
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 @@
.globl __kernel_sigreturn
.type __kernel_sigreturn,@function
+ nop /* this guy is needed for .LSTARTFDEDLSI1 below (watch for HACK) */

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