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

[Eduard Zingerman <eddyz87@gmail.com>]

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

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