[bpf-next,v1,0/4] 'bpf_fastcall' attribute in vmlinux.h and bpf_helper_defs.h

Message

Eduard Zingerman Sept. 16, 2024, 9:17 a.m. UTC

The goal of this patch-set is to reflect attribute bpf_fastcall
for supported helpers and kfuncs in generated header files.
For helpers this requires a tweak for scripts/bpf_doc.py and an update
to uapi/linux/bpf.h doc-comment.
For kfuncs this requires:
- introduction of a new KF_FASTCALL flag;
- modification to pahole to read kfunc flags and generate
  DECL_TAG "bpf_fastcall" for marked kfuncs;
- modification to bpftool to scan for DECL_TAG "bpf_fastcall"
  presence.

In both cases the following helper macro is defined in the generated
header:

    #ifndef __bpf_fastcall
    #if __has_attribute(bpf_fastcall)
    #define __bpf_fastcall __attribute__((bpf_fastcall))
    #else
    #define __bpf_fastcall
    #endif
    #endif

And is used to mark appropriate function prototypes. More information
about bpf_fastcall attribute could be found in [1] and [2].

Modifications to pahole are submitted separately.

[1] LLVM source tree commit:
    64e464349bfc ("[BPF] introduce __attribute__((bpf_fastcall))")

[2] Linux kernel tree commit (note: feature was renamed from
    no_caller_saved_registers to bpf_fastcall after this commit):
    52839f31cece ("Merge branch 'no_caller_saved_registers-attribute-for-helper-calls'")

Eduard Zingerman (4):
  bpf: allow specifying bpf_fastcall attribute for BPF helpers
  bpf: __bpf_fastcall for bpf_get_smp_processor_id in uapi
  bpf: use KF_FASTCALL to mark kfuncs supporting fastcall contract
  bpftool:  __bpf_fastcall for kfuncs marked with special decl_tag

 include/linux/btf.h            |  1 +
 include/uapi/linux/bpf.h       |  2 +
 kernel/bpf/helpers.c           |  4 +-
 kernel/bpf/verifier.c          |  5 +-
 scripts/bpf_doc.py             | 50 ++++++++++++++++-
 tools/bpf/bpftool/btf.c        | 98 ++++++++++++++++++++++++++++++----
 tools/include/uapi/linux/bpf.h |  2 +
 7 files changed, 144 insertions(+), 18 deletions(-)

Comments

Eduard Zingerman Sept. 16, 2024, 9:22 a.m. UTC | #1

On Mon, 2024-09-16 at 02:17 -0700, Eduard Zingerman wrote:

> Modifications to pahole are submitted separately.

Note, corresponding pahole changes are submitted here:
https://lore.kernel.org/bpf/[e-mail]/

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