Re: [PATCH bpf-next 0/7] bpftool: Add LLVM as default library for disassembling JIT-ed programs

["Niklas Söderlund" <niklas.soderlund@corigine.com>]

Hi Quentin,

Thanks for your work.

On 2022-09-06 14:36:06 +0100, Quentin Monnet wrote:
> To disassemble instructions for JIT-ed programs, bpftool has relied on the
> libbfd library. This has been problematic in the past: libbfd's interface
> is not meant to be stable and has changed several times, hence the
> detection of the two related features from the Makefile
> (disassembler-four-args and disassembler-init-styled). When it comes to
> shipping bpftool, this has also caused issues with several distribution
> maintainers unwilling to support the feature (for example, Debian's page
> for binutils-dev, libbfd's package, says: "Note that building Debian
> packages which depend on the shared libbfd is Not Allowed.").
> 
> This patchset adds support for LLVM as the primary library for
> disassembling instructions for JIT-ed programs.
> 
> We keep libbfd as a fallback. One reason for this is that currently it
> works well, we have all we need in terms of features detection in the
> Makefile, so it provides a fallback for disassembling JIT-ed programs if
> libbfd is installed but LLVM is not. The other reason is that libbfd
> supports nfp instruction for Netronome's SmartNICs and can be used to
> disassemble offloaded programs, something that LLVM cannot do (Niklas
> confirmed that the feature is still in use). However, if libbfd's interface
> breaks again in the future, we might reconsider keeping support for it.

I have tested the fallback method for NFP and it works as expected and 
one can dump the offloaded program. I know there is discussion about the 
output format of the LLVM path, but for the whole series from a NFP 
point of view,

Tested-by: Niklas Söderlund <niklas.soderlund@corigine.com>

> 
> Quentin Monnet (7):
>   bpftool: Define _GNU_SOURCE only once
>   bpftool: Remove asserts from JIT disassembler
>   bpftool: Split FEATURE_TESTS/FEATURE_DISPLAY definitions in Makefile
>   bpftool: Group libbfd defs in Makefile, only pass them if we use
>     libbfd
>   bpftool: Refactor disassembler for JIT-ed programs
>   bpftool: Add LLVM as default library for disassembling JIT-ed programs
>   bpftool: Add llvm feature to "bpftool version"
> 
>  .../bpftool/Documentation/common_options.rst  |   8 +-
>  tools/bpf/bpftool/Makefile                    |  65 +++--
>  tools/bpf/bpftool/common.c                    |   2 +
>  tools/bpf/bpftool/iter.c                      |   2 +
>  tools/bpf/bpftool/jit_disasm.c                | 244 ++++++++++++++----
>  tools/bpf/bpftool/main.c                      |  10 +
>  tools/bpf/bpftool/main.h                      |  29 ++-
>  tools/bpf/bpftool/map.c                       |   1 -
>  tools/bpf/bpftool/net.c                       |   2 +
>  tools/bpf/bpftool/perf.c                      |   2 +
>  tools/bpf/bpftool/prog.c                      |  17 +-
>  tools/bpf/bpftool/xlated_dumper.c             |   2 +
>  12 files changed, 291 insertions(+), 93 deletions(-)
> 
> -- 
> 2.34.1
> 

-- 
Kind Regards,
Niklas Söderlund