Re: [PATCH -rc v1] gcov: Disable gcov build with GCC 10

[Colin Ian King <colin.king@canonical.com>]

On 10/09/2020 13:52, Peter Oberparleiter wrote:
> On 04.09.2020 17:58, Leon Romanovsky wrote:
>> GCOV built with GCC 10 doesn't initialize n_function variable.
>> This produces different kernel panics as was seen by Colin in
>> Ubuntu [1] and me in FC 32 [2].
>>
>> As a workaround, let's disable GCOV build for broken GCC 10 version.
>>
>> [1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1891288
>> [2] https://lore.kernel.org/lkml/20200827133932.3338519-1-leon@kernel.org
>> Cc: Colin Ian King <colin.king@canonical.com>
>> Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
> 
> The following patch should fix the problem with gcov and GCC 10.
> I successfully tested it with kernel 5.9-rc4 on s390 using GCC 10.1.1
> and also with GCC 9.1.1 to see that it didn't break support for previous
> GCC versions. In both cases there were no kernel panics and gcov worked
> fine.
> 
> Could you try this patch to see if it also fixes the problem in your
> environment?
> 

This works perfectly, tested with gcc 10.2 on linux 5.9-rc4 (tip) on an
ARM64 Socionext Synquacer E-Series (Cortex A-53) system.

thanks!

Tested-and-Acked-by: Colin Ian King <colin.king@canonical.com>

> ---8<---
> From: Peter Oberparleiter <oberpar@linux.ibm.com>
> Subject: [PATCH] gcov: add support for GCC 10.1
> 
> Using gcov to collect coverage data for kernels compiled with GCC 10.1
> causes random malfunctions and kernel crashes. This is the result of a
> changed GCOV_COUNTERS value in GCC 10.1 that causes a mismatch between
> the layout of the gcov_info structure created by GCC profiling code and
> the related structure used by the kernel.
> 
> Fix this by updating the in-kernel GCOV_COUNTERS value. Also re-enable
> config GCOV_KERNEL for use with GCC 10.
> 
> Reported-by: Colin Ian King <colin.king@canonical.com>
> Reported-by: Leon Romanovsky <leonro@nvidia.com>
> Signed-off-by: Peter Oberparleiter <oberpar@linux.ibm.com>
> ---
>  kernel/gcov/Kconfig   | 1 -
>  kernel/gcov/gcc_4_7.c | 4 +++-
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/gcov/Kconfig b/kernel/gcov/Kconfig
> index bb4b680e8455..3110c77230c7 100644
> --- a/kernel/gcov/Kconfig
> +++ b/kernel/gcov/Kconfig
> @@ -4,7 +4,6 @@ menu "GCOV-based kernel profiling"
>  config GCOV_KERNEL
>  	bool "Enable gcov-based kernel profiling"
>  	depends on DEBUG_FS
> -	depends on !CC_IS_GCC || GCC_VERSION < 100000
>  	select CONSTRUCTORS if !UML
>  	default n
>  	help
> diff --git a/kernel/gcov/gcc_4_7.c b/kernel/gcov/gcc_4_7.c
> index 908fdf5098c3..53c67c87f141 100644
> --- a/kernel/gcov/gcc_4_7.c
> +++ b/kernel/gcov/gcc_4_7.c
> @@ -19,7 +19,9 @@
>  #include <linux/vmalloc.h>
>  #include "gcov.h"
> 
> -#if (__GNUC__ >= 7)
> +#if (__GNUC__ >= 10)
> +#define GCOV_COUNTERS			8
> +#elif (__GNUC__ >= 7)
>  #define GCOV_COUNTERS			9
>  #elif (__GNUC__ > 5) || (__GNUC__ == 5 && __GNUC_MINOR__ >= 1)
>  #define GCOV_COUNTERS			10
>