[dwarves,v6,0/3] pahole: Inject kfunc decl tags into BTF

Message

Daniel Xu March 25, 2024, 5:53 p.m. UTC

This patchset teaches pahole to parse symbols in .BTF_ids section in
vmlinux and discover exported kfuncs. Pahole then takes the list of
kfuncs and injects a BTF_KIND_DECL_TAG for each kfunc.

Example of encoding:

        $ bpftool btf dump file .tmp_vmlinux.btf | rg "DECL_TAG 'bpf_kfunc'" | wc -l
        121

        $ bpftool btf dump file .tmp_vmlinux.btf | rg 56337
        [56337] FUNC 'bpf_ct_change_timeout' type_id=56336 linkage=static
        [127861] DECL_TAG 'bpf_kfunc' type_id=56337 component_idx=-1

This enables downstream users and tools to dynamically discover which
kfuncs are available on a system by parsing vmlinux or module BTF, both
available in /sys/kernel/btf.

This feature is enabled with --btf_features=decl_tag,decl_tag_kfuncs.

=== Changelog ===

Changes from v5:
* Add gobuffer__sort() helper
* Use strstarts() instead of strncmp()
* Use uint64_t instead of size_t
* Add clarifying comments for get_func_name()

Changes from v4:
* Update man page with decl_tag_kfuncs feature
* Fix release mode build warnings
* Add elf_getshrstrndx() error checking
* Disable tagging if decl_tag feature is off
* Fix malformed func name handling

Changes from v3:
* Guard kfunc tagging behind feature flag
* Use struct btf_id_set8 definition
* Remove unnecessary member from btf_encoder
* Fix code styling

Changes from v2:
* More reliably detect kfunc membership in set8 by tracking set addr ranges
* Rename some variables/functions to be more clear about kfunc vs func

Changes from v1:
* Fix resource leaks
* Fix callee -> caller typo
* Rename btf_decl_tag from kfunc -> bpf_kfunc
* Only grab btf_id_set funcs tagged kfunc
* Presort btf func list

Daniel Xu (3):
  gobuffer: Add gobuffer__sort() helper
  pahole: Add --btf_feature=decl_tag_kfuncs feature
  pahole: Inject kfunc decl tags into BTF

 btf_encoder.c      | 374 +++++++++++++++++++++++++++++++++++++++++++++
 dwarves.h          |   1 +
 gobuffer.c         |   5 +
 gobuffer.h         |   2 +
 man-pages/pahole.1 |   1 +
 pahole.c           |   1 +
 6 files changed, 384 insertions(+)

Comments

Arnaldo Carvalho de Melo April 2, 2024, 8:24 p.m. UTC | #1

On Mon, Mar 25, 2024 at 11:53:36AM -0600, Daniel Xu wrote:
> This patchset teaches pahole to parse symbols in .BTF_ids section in
> vmlinux and discover exported kfuncs. Pahole then takes the list of
> kfuncs and injects a BTF_KIND_DECL_TAG for each kfunc.
> 
> Example of encoding:
> 
>         $ bpftool btf dump file .tmp_vmlinux.btf | rg "DECL_TAG 'bpf_kfunc'" | wc -l
>         121
> 
>         $ bpftool btf dump file .tmp_vmlinux.btf | rg 56337
>         [56337] FUNC 'bpf_ct_change_timeout' type_id=56336 linkage=static
>         [127861] DECL_TAG 'bpf_kfunc' type_id=56337 component_idx=-1
> 
> This enables downstream users and tools to dynamically discover which
> kfuncs are available on a system by parsing vmlinux or module BTF, both
> available in /sys/kernel/btf.
> 
> This feature is enabled with --btf_features=decl_tag,decl_tag_kfuncs.
> 
> === Changelog ===

I'm a bit lagged on my backlog, will try and process these soon,

- Arnaldo
 
> Changes from v5:
> * Add gobuffer__sort() helper
> * Use strstarts() instead of strncmp()
> * Use uint64_t instead of size_t
> * Add clarifying comments for get_func_name()
> 
> Changes from v4:
> * Update man page with decl_tag_kfuncs feature
> * Fix release mode build warnings
> * Add elf_getshrstrndx() error checking
> * Disable tagging if decl_tag feature is off
> * Fix malformed func name handling
> 
> Changes from v3:
> * Guard kfunc tagging behind feature flag
> * Use struct btf_id_set8 definition
> * Remove unnecessary member from btf_encoder
> * Fix code styling
> 
> Changes from v2:
> * More reliably detect kfunc membership in set8 by tracking set addr ranges
> * Rename some variables/functions to be more clear about kfunc vs func
> 
> Changes from v1:
> * Fix resource leaks
> * Fix callee -> caller typo
> * Rename btf_decl_tag from kfunc -> bpf_kfunc
> * Only grab btf_id_set funcs tagged kfunc
> * Presort btf func list
> 
> Daniel Xu (3):
>   gobuffer: Add gobuffer__sort() helper
>   pahole: Add --btf_feature=decl_tag_kfuncs feature
>   pahole: Inject kfunc decl tags into BTF
> 
>  btf_encoder.c      | 374 +++++++++++++++++++++++++++++++++++++++++++++
>  dwarves.h          |   1 +
>  gobuffer.c         |   5 +
>  gobuffer.h         |   2 +
>  man-pages/pahole.1 |   1 +
>  pahole.c           |   1 +
>  6 files changed, 384 insertions(+)
> 
> -- 
> 2.44.0