This is version #2 of the gcov kernel support patch set (see further

below for an in-depth explanation). Patch base is 2.6.26-rc3.
Changes are mostly based on mailing list feedback:
 * added more documentation

 * moved gcov config menu to general setup

 * renamed some structures and variables (removed _t, lowercase ctors)

 * split mod versioning change into separate patch (3)

 * split GCC_VERSION_LOWER into separate patch (2)

 * split gcov core patch into two patches (5+6) for better readability

 * absolute paths only used when CONFIG_GCOV_PROFILE is set

 * fixed compile problem with CONFIG_MODULES=n

 * fixed memory leak in gcov fs code

 * more style changes
Patch overview:
[PATCH 1/7] kernel: call constructors

[PATCH 2/7] kernel: introduce GCC_VERSION_LOWER macro

[PATCH 3/7] kbuild: delay object file renaming during module versioning

[PATCH 4/7] seq_file: add function to write binary data

[PATCH 5/7] gcov: add gcov profiling infrastructure

[PATCH 6/7] kbuild: make source and include paths absolute

[PATCH 7/7] gcov: architecture specific compile flag adjustments
===
This set of patches enables the use of GCC's coverage testing tool

gcov [1] with kernel 2.6.25. Coverage data for the running kernel is

exported via debugfs in a gcov-compatible format. To get coverage

data for a specific file, simply use gcov with the -o option:
# gcov -o /sys/kernel/debug/gcov/tmp/linux-2.6.25/kernel spinlock.c
This will create source code files annotated with execution counts

in the current directory. In addition, graphical gcov front-ends such

as lcov [2] can be used to automate the process of collecting data

for the entire kernel and provide coverage overviews in HTML format.
Possible uses:
* debugging (has this line been executed at all?)

* test improvement (how do I change my test to cover these lines?)

* minimizing kernel configurations (do I need this option if the

  associated code is never executed?)
Known issues:
* some architecture specific problems: the patch...
[ message continues ]

powerpc blew up:
/opt/crosstool/gcc-4.1.0-glibc-2.3.6/powerpc64-unknown-linux-gnu/lib/gcc/powerpc64-unknown-linux-gnu/4.1.0/../../../../powerpc64-unknown-linux-gnu/bin/ld: skipping incompatible /opt/crosstool/gcc-4.1.0-glibc-2.3.6/powerpc64-unknown-linux-gnu/lib/gcc/powerpc64-unknown-linux-gnu/4.1.0/./libgcov.a when searching for -lgcov

/opt/crosstool/gcc-4.1.0-glibc-2.3.6/powerpc64-unknown-linux-gnu/lib/gcc/powerpc64-unknown-linux-gnu/4.1.0/../../../../powerpc64-unknown-linux-gnu/bin/ld: cannot find -lgcov

collect2: ld returned 1 exit status

make[2]: *** [arch/powerpc/kernel/vdso32/vdso32.so.dbg] Error 1

make[1]: *** [arch/powerpc/kernel/vdso32] Error 2
--

This looks like a secondary linking process. It's best to exclude the

whole directory from GCOV profiling (which should ony work for C files

anyway).
Below is an update for patch #7 of the gcov series that includes the

corresponding changes.
---
[PATCH 7/7] gcov: architecture specific compile flag adjustments
From: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
Exclude code from profiling which is not linked to the main kernel or

which is running in a context not compatible with the assumptions made

by gcc's profiling code.
Signed-off-by: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>

---

 arch/arm/boot/compressed/Makefile      |    1 +

 arch/powerpc/kernel/vdso32/Makefile    |    1 +

 arch/powerpc/kernel/vdso64/Makefile    |    1 +

 arch/ppc/boot/Makefile                 |    1 +

 arch/ppc/boot/common/Makefile          |    1 +

 arch/ppc/boot/simple/Makefile          |    1 +

 arch/x86/boot/Makefile                 |    1 +

 arch/x86/boot/compressed/Makefile      |    1 +

 arch/x86/kernel/acpi/realmode/Makefile |    1 +

 9 files changed, 9 insertions(+)
Index: linux-2.6.26-rc3/arch/arm/boot/compressed/Makefile

===================================================================

--- linux-2.6.26-rc3.orig/arch/arm/boot/compressed/Makefile

+++ linux-2.6.26-rc3/arch/arm/boot/compressed/Makefile

@@ -7,6 +7,7 @@

 HEAD	= head.o

 OBJS	= misc.o

 FONTC	= $(srctree)/drivers/video/console/font_acorn_8x8.c

+GCOV	:= n
 #

 # Architecture dependencies

Index: linux-2.6.26-rc3/arch/x86/boot/compressed/Makefile

===================================================================

--- linux-2.6.26-rc3.orig/arch/x86/boot/compressed/Makefile

+++ linux-2.6.26-rc3/arch/x86/boot/compressed/Makefile

@@ -12,6 +12,7 @@ cflags-$(CONFIG_X86_64) := -mcmodel=smal

 KBUILD_CFLAGS += $(cflags-y)

 KBUILD_CFLAGS += $(call cc-option,-ffreestanding)

 KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)

+GCOV := n
 KBUILD_AFLAGS  := $(KBUILD_CFLAGS) -D__ASSEMBLY__...
[ message continues ]

Sounds like your toolchain was built without biarch support, but you're

using it for the 32-bit parts of the kernel anyway.  Which works as long

as you're not using any libraries, but now you need libgcov.a .
What does
/opt/crosstool/gcc-4.1.0-glibc-2.3.6/powerpc64-unknown-linux-gnu/bin/

powerpc64-unknown-linux-gnu-gcc -v
say?  (Or whatever the correct path to that compiler is, the directory

structure is a bit unusual here it seems).  There shouldn't be a

--disable-biarch there.
Or, what does
find

/opt/crosstool/gcc-4.1.0-glibc-2.3.6/powerpc64-unknown-linux-gnu/4.1.0/

-name libgcov.a
say?  (It should usually find three versions: 64-bit, 32-bit, 32-bit no

float).
You *can* build with a non-biarch compiler, but then you need to point

the kernel build system at a 32-bit toolchain to use for the 32-bit

parts (via CROSS32_COMPILE).
Segher
--

y:/home/akpm> /opt/crosstool/gcc-4.1.0-glibc-2.3.6/powerpc64-unknown-linux-gnu/bin/powerpc64-unknown-linux-gnu-gcc -v

Using built-in specs.

Target: powerpc64-unknown-linux-gnu

Configured with: /home/axboe/crosstool-0.43/build/powerpc64-unknown-linux-gnu/gcc-4.1.0-glibc-2.3.6/gcc-4.1.0/configure --target=powerpc64-unknown-linux-gnu --host=x86_64-host_unknown-linux-gnu --prefix=/opt/crosstool/gcc-4.1.0-glibc-2.3.6/powerpc64-unknown-linux-gnu --disable-multilib --with-sysroot=/opt/crosstool/gcc-4.1.0-glibc-2.3.6/powerpc64-unknown-linux-gnu/powerpc64-unknown-linux-gnu/sys-root --with-local-prefix=/opt/crosstool/gcc-4.1.0-glibc-2.3.6/powerpc64-unknown-linux-gnu/powerpc64-unknown-linux-gnu/sys-root --disable-nls --enable-threads=posix --enable-symvers=gnu --enable-__cxa_atexit --enable-languages=c --enable-shared --enable-c99 --enable-long-long

Thread model: posix
Only a single hit:
/opt/crosstool/gcc-4.1.0-glibc-2.3.6/powerpc64-unknown-linux-gnu/lib/gcc/powerpc64-unknown-linux-gnu/4.1.0/libgcov.a
and it contains
y:/home/akpm/ppc> ar x libgcov.a

y:/home/akpm/ppc> l

total 316

-rw-r--r-- 1 akpm akpm  44192 May 23 09:53 _gcov.o

-rw-r--r-- 1 akpm akpm   8448 May 23 09:53 _gcov_execl.o

-rw-r--r-- 1 akpm akpm   8584 May 23 09:53 _gcov_execle.o

-rw-r--r-- 1 akpm akpm   8456 May 23 09:53 _gcov_execlp.o

-rw-r--r-- 1 akpm akpm   7384 May 23 09:53 _gcov_execv.o

-rw-r--r-- 1 akpm akpm   7544 May 23 09:53 _gcov_execve.o

-rw-r--r-- 1 akpm akpm   7392 May 23 09:53 _gcov_execvp.o

-rw-r--r-- 1 akpm akpm   7264 May 23 09:53 _gcov_fork.o

-rw-r--r-- 1 akpm akpm   7240 May 23 09:53 _gcov_interval_profiler.o

-rw-r--r-- 1 akpm akpm   7464 May 23 09:53 _gcov_merge_add.o

-rw-r--r-- 1 akpm akpm   8544 May 23 09:53 _gcov_merge_delta.o

-rw-r--r-- 1 akpm akpm   8488 May 23 09:53 _gcov_merge_single.o

-rw-r--r-- 1 akpm akpm   6976 May 23 09:53 _gcov_one_value_profiler.o

-rw-r--r-- 1 akpm akpm   6856 May 23 09:53 _gcov_pow2_profiler.o

-rw-r--r-- 1 akpm akpm 146492 May 23 09:52 libgcov.a

y:/home/akpm/ppc...
[ message continues ]

That's the culprit.  I believe 4.1.0 enables multilib by default on

PowerPC

compilers that target 64-bit by default (the patch for that is dated

almost

a full year before the 4.1.0 release).  I have no idea why crosstool

disables this support; perhaps there were some problems with some older
You were lucky, yes.  If your compiler would have been just a little

bit older it wouldn't have been able to build 32-bit at all.
Do you have a separate 32-bit PowerPC compiler?  If so, just set

CROSS32_COMPILE to it; if not, you'll need a new toolchain.  In

that case, it's probably worthwhile to upgrade to 4.1.2 at least...
Segher
--

On Fri, 23 May 2008 23:52:43 +0200
Sigh.  Life's too short.  I'll go back to testing powerpc builds on the

powerpc box.
--

I reviewed the patches and they look good to me (except for

some minor nits, probably not worth fixing)
-Andi

--