NACK/Cmnt: [SRU JAMMY] [PATCH] UBUNTU: SAUCE: scripts/pahole-flags.sh: Add --skip_encoding_btf_enum64 for pahole versions >= 124

[Stefan Bader]

On 29.01.24 11:19, Stefan Bader wrote:
> On 26.01.24 19:54, mitchell.augustin at canonical.com wrote:
>> From: Mitchell Augustin <mitchell.augustin at canonical.com>
>>
>> BugLink: https://bugs.launchpad.net/bugs/2051376
>>
>> UpstreamStatus: Merged with 5.15.148
>>
>> This patch will not go upstream since 6.7-rc1 converts this script 
>> into a makefile snippet, and since this patch is already present
>> in upstream 5.15.148 and the master branch for Noble.
>>
>> New pahole (version 1.24) generates by default new BTF_KIND_ENUM64 BTF 
>> tag,
>> which is not supported by stable kernel.
>>
>> As a result the kernel with CONFIG_DEBUG_INFO_BTF option will fail to
>> compile with following error:
>>
>>    BTFIDS  vmlinux
>> FAILED: load BTF from vmlinux: Invalid argument
>>
>> New pahole provides --skip_encoding_btf_enum64 option to skip 
>> BTF_KIND_ENUM64
>> generation and produce BTF supported by stable kernel.
>>
>> (cherry picked from commit b775fbf532dc01ae53a6fc56168fd30cb4b0c658 in 
>> 5.15.148 tree)
>>
>> Signed-off-by: Mitchell Augustin <mitchell.augustin at canonical.com>
>> ---
> 
> Rejected for the following reasons:
> Ok, so this patch is taken from the upstream stable repository. In which 
> case the proper provenance (including commit message) needs to be 
> preserved. That is if there is a need for speed. Eventually all 
> linux-5.15.y will be picked into Jammy, we just lag a bit behind 
> (currently we have 5.15.143 committed).
> So what the patch should look like is:
> 
>  From b775fbf532dc01ae53a6fc56168fd30cb4b0c658 Mon Sep 17 00:00:00 2001
> From: Martin Rodriguez Reboredo <yakoyoku at gmail.com>
> Date: Sun, 4 Sep 2022 15:19:01 +0200
> Subject: [PATCH] kbuild: Add skip_encoding_btf_enum64 option to pahole
> 
> BugLink: https://bugs.launchpad.net/bugs/2051376
> 
> New pahole (version 1.24) generates by default new BTF_KIND_ENUM64 BTF tag,
> which is not supported by stable kernel.
> 
> As a result the kernel with CONFIG_DEBUG_INFO_BTF option will fail to
> compile with following error:
> 
>    BTFIDS  vmlinux
> FAILED: load BTF from vmlinux: Invalid argument
> 
> New pahole provides --skip_encoding_btf_enum64 option to skip 
> BTF_KIND_ENUM64
> generation and produce BTF supported by stable kernel.
> 
> Adding this option to scripts/pahole-flags.sh.
> 
> This change does not have equivalent commit in linus tree, because linus 
> tree
> has support for BTF_KIND_ENUM64 tag, so it does not need to be disabled.

I think this ^ in the upstream stable commit message answered the 
question I asked below. So it is the kernel build environment that 
matters. And only the old kernel version requires adjustment when being 
compiled with a pahole version 1.24 or later.

> 
> Signed-off-by: Martin Rodriguez Reboredo <yakoyoku at gmail.com>
> Signed-off-by: Jiri Olsa <jolsa at kernel.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> 
> (cherry picked from commit b775fbf532dc01ae53a6fc56168fd30cb4b0c658 
> linux-5.15.y)
> Signed-off-by: Mitchell Augustin <mitchell.augustin at canonical.com>
> ---
>   scripts/pahole-flags.sh | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> ...
> 
> The second question I had in previous replies was whether we also need 
> to do something for HWE kernels. Jammy (5.15) fails to compile when 
> pahole >= 1.24 is available. This must be a configuration other than 
> what we use by default for the distro, otherwise we should have seen 
> this. But we also have HWE kernels (now 6.5, at some point 6.8). I 
> currently do not see something adjusted in the 6.5 kernel. That might 
> mean in Mantic there is a pahole version which does not have the 
> problem. Or it is the kernel Makefiles which got adjusted, so this is no 
> longer necessary.
> 
> -Stefan
>>   scripts/pahole-flags.sh | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
>> index ac8b23787427..d38fa6d84d62 100755
>> --- a/scripts/pahole-flags.sh
>> +++ b/scripts/pahole-flags.sh
>> @@ -4,7 +4,7 @@
>>   extra_paholeopt=
>>   if ! [ -x "$(command -v ${PAHOLE})" ]; then
>> -    return
>> +    exit 0
>>   fi
>>   pahole_ver=$($(dirname $0)/pahole-version.sh ${PAHOLE})
>> @@ -17,4 +17,8 @@ if [ "${pahole_ver}" -ge "121" ]; then
>>       extra_paholeopt="${extra_paholeopt} --btf_gen_floats"
>>   fi
>> +if [ "${pahole_ver}" -ge "124" ]; then
>> +    extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_enum64"
>> +fi
>> +
>>   echo ${extra_paholeopt}
> 
> 

-- 
- Stefan

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