Re: [PATCH bpf-next v2] bpftool: improve btf c dump sorting stability

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

On 06/09/2024 20:56, Eduard Zingerman wrote:
> On Fri, 2024-09-06 at 14:24 +0100, Mykyta Yatsenko wrote:
>> From: Mykyta Yatsenko <yatsenko@meta.com>
>>
>> Existing algorithm for BTF C dump sorting uses only types and names of
>> the structs and unions for ordering. As dump contains structs with the
>> same names but different contents, relative to each other ordering of
>> those structs will be accidental.
>> This patch addresses this problem by introducing a new sorting field
>> that contains hash of the struct/union field names and types to
>> disambiguate comparison of the non-unique named structs.
>>
>> Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
>> ---
> Note, this is still not fully stable, e.g.:
>
> $ for i in $(seq 1 10); \
>    do touch ./kernel/bpf/verifier.c && \
>       ccache-kernel-make.sh -j23 && \
>       ./tools/bpf/bpftool/bpftool btf dump file vmlinux format c > ~/work/tmp/vmlinux.h.$i; \
>    done
>    ...
> $ md5sum ~/work/tmp/vmlinux.h.* | sort -k1
> 76c9b22274c4aa6253ffaafa33ceffd3  /home/eddy/work/tmp/vmlinux.h.2
> 76c9b22274c4aa6253ffaafa33ceffd3  /home/eddy/work/tmp/vmlinux.h.4
> a1c90a62e6cca59869a9cdffbaa3c4de  /home/eddy/work/tmp/vmlinux.h.1
> a1c90a62e6cca59869a9cdffbaa3c4de  /home/eddy/work/tmp/vmlinux.h.10
> a1c90a62e6cca59869a9cdffbaa3c4de  /home/eddy/work/tmp/vmlinux.h.3
> a1c90a62e6cca59869a9cdffbaa3c4de  /home/eddy/work/tmp/vmlinux.h.5
> a1c90a62e6cca59869a9cdffbaa3c4de  /home/eddy/work/tmp/vmlinux.h.6
> a1c90a62e6cca59869a9cdffbaa3c4de  /home/eddy/work/tmp/vmlinux.h.7
> a1c90a62e6cca59869a9cdffbaa3c4de  /home/eddy/work/tmp/vmlinux.h.8
> a1c90a62e6cca59869a9cdffbaa3c4de  /home/eddy/work/tmp/vmlinux.h.9
>
> [...]
>
Interesting, thanks for showing this, I'll try to replicate this test.