[3.11.y.z extended stable] Patch "x86, hweight: Fix BUG when booting with CONFIG_GCOV_PROFILE_ALL=y" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    x86, hweight: Fix BUG when booting with CONFIG_GCOV_PROFILE_ALL=y

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 1c2a9d9f943d457957c8ea8ca8ea378bceeb4e05 Mon Sep 17 00:00:00 2001
From: Peter Oberparleiter <oberpar at linux.vnet.ibm.com>
Date: Thu, 6 Feb 2014 15:58:20 +0100
Subject: x86, hweight: Fix BUG when booting with CONFIG_GCOV_PROFILE_ALL=y

commit 6583327c4dd55acbbf2a6f25e775b28b3abf9a42 upstream.

Commit d61931d89b, "x86: Add optimized popcnt variants" introduced
compile flag -fcall-saved-rdi for lib/hweight.c. When combined with
options -fprofile-arcs and -O2, this flag causes gcc to generate
broken constructor code. As a result, a 64 bit x86 kernel compiled
with CONFIG_GCOV_PROFILE_ALL=y prints message "gcov: could not create
file" and runs into sproadic BUGs during boot.

The gcc people indicate that these kinds of problems are endemic when
using ad hoc calling conventions.  It is therefore best to treat any
file compiled with ad hoc calling conventions as an isolated
environment and avoid things like profiling or coverage analysis,
since those subsystems assume a "normal" calling conventions.

This patch avoids the bug by excluding lib/hweight.o from coverage
profiling.

Reported-by: Meelis Roos <mroos at linux.ee>
Cc: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Peter Oberparleiter <oberpar at linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/52F3A30C.7050205@linux.vnet.ibm.com
Signed-off-by: H. Peter Anvin <hpa at zytor.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 lib/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/Makefile b/lib/Makefile
index 7baccfd..fc2f9ef 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -45,6 +45,7 @@ lib-$(CONFIG_RWSEM_GENERIC_SPINLOCK) += rwsem-spinlock.o
 lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
 lib-$(CONFIG_PERCPU_RWSEM) += percpu-rwsem.o

+GCOV_PROFILE_hweight.o := n
 CFLAGS_hweight.o = $(subst $(quote),,$(CONFIG_ARCH_HWEIGHT_CFLAGS))
 obj-$(CONFIG_GENERIC_HWEIGHT) += hweight.o

--
1.8.3.2