linux-kernel - Re: GCOV doesn't seem to work on ARM with kernel 2.6.35-rc6

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Message-id: <4C50342F.2080001@samsung.local>
Date:	Wed, 28 Jul 2010 15:44:15 +0200
From:	Karol Lewandowski <k.lewandowsk@...sung.com>
To:	Peter Oberparleiter <oberpar@...ux.vnet.ibm.com>
Cc:	Karol Lewandowski <k.lewandowsk@...sung.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: GCOV doesn't seem to work on ARM with kernel 2.6.35-rc6

On 07/28/2010 03:12 PM, Peter Oberparleiter wrote:
> On 27.07.2010 09:35, Karol Lewandowski wrote:
>> On 07/26/2010 06:57 PM, Peter Oberparleiter wrote:
>>> Karol Lewandowski wrote:
>>>> On 07/26/2010 12:32 PM, Karol Lewandowski wrote:
>>>>> I'm trying to use code coverage measurements with mainline Linux kernel
>>>>> 2.6.35-rc6 on ARM platform (specifically on Samsung's S5PC110 board).
>> ...
>>> I just tested gcov support for 2.6.35-rc6 on s390 and it works without
>>> a problem. My assumption would be that you are using an EABI-GCC to
>>> compile your kernel. Those compilers name their constructor symbols
>>
>> Exactly.
>>
>>> differently than the vanilla GCC so that the whole constructor calling
>>> mechanism on which the gcov support relies, will fail. If that is
>>> indeed the case, the following testing patch should solve your
>>> problem:
>>
>> Yes, that was the case and your patch indeed solved my problem.
>
> Excellent. I could imagine that other ARM users might also benefit from
> this patch. Before I submit it for integration though, I need to make
> sure that it also works for kernel modules. Could you enable profiling
> for a kernel module and verify that you are seeing files in
> /sys/kernel/debug/gcov belonging to that module??

That does work too.

However, having seen this[x] patch I would ask if constructor name might 
be dynamically selected via user-(in)visible Kconfig option (like in 
that patch?)  I've tested it and it does seem to work too.

[x] 
http://groups.google.com/group/linux.kernel/browse_thread/thread/84439151c5386e0f/d7dbec62b9d7989f?show_docid=d7dbec62b9d7989f

I've copy pasted interesting parts from that patch below - I'm sure you 
get the idea.

Thanks.

--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -442,7 +442,7 @@
  #ifdef CONFIG_CONSTRUCTORS
  #define KERNEL_CTORS() . = ALIGN(8);                      \
                         VMLINUX_SYMBOL(__ctors_start) = .; \
-                       *(.ctors)                          \
+                       *(CONFIG_GCOV_CTORS)               \

--- a/kernel/gcov/Kconfig
+++ b/kernel/gcov/Kconfig
+config GCOV_CTORS
+       string
+       depends on GCOV_KERNEL
+       default ".init_array" if ARM && AEABI
+       default ".ctors"

--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2296,7 +2296,7 @@ static noinline struct module *load_module(void 
__user *umod,
                                             "__kcrctab_unused_gpl");
  #endif
  #ifdef CONFIG_CONSTRUCTORS
-       mod->ctors = section_objs(hdr, sechdrs, secstrings, ".ctors",
+       mod->ctors = section_objs(hdr, sechdrs, secstrings, 
CONFIG_GCOV_CTORS, sizeof(*mod->ctors), &mod->num_ctors);
--
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