[PATCH bpf-next v3 0/3] bpf: Reduce verifier stack frame size

[Yonghong Song <yonghong.song@linux.dev>]

Arnd Bergmann reported an issue ([1]) where clang compiler (less than
llvm18) may trigger an error where the stack frame size exceeds the limit.
I can reproduce the error like below:
  kernel/bpf/verifier.c:24491:5: error: stack frame size (2552) exceeds limit (1280) in 'bpf_check'
      [-Werror,-Wframe-larger-than]
  kernel/bpf/verifier.c:19921:12: error: stack frame size (1368) exceeds limit (1280) in 'do_check'
      [-Werror,-Wframe-larger-than]

This patch series fixed the above two errors by reducing stack size.
See each individual patches for details.

  [1] https://lore.kernel.org/bpf/20250620113846.3950478-1-arnd@kernel.org/

Changelogs:
  v2 -> v3:
    - v2: https://lore.kernel.org/bpf/20250702171134.2370432-1-yonghong.song@linux.dev/
    - Rename env->callchain to env->callchain_buf so it is clear that
    - env->callchain_buf is used for a temp buf.
      
  v1 -> v2:
    - v1: https://lore.kernel.org/bpf/20250702053332.1991516-1-yonghong.song@linux.dev/
    - Simplify assignment to struct bpf_insn pointer in do_misc_fixups().
    - Restore original implementation in opt_hard_wire_dead_code_branches()
      as only one insn on the stack.
    - Avoid unnecessary insns for 64bit modulo (mod 0/-1) operations.

Yonghong Song (3):
  bpf: Simplify assignment to struct bpf_insn pointer in
    do_misc_fixups()
  bpf: Reduce stack frame size by using env->insn_buf for bpf insns
  bpf: Avoid putting struct bpf_scc_callchain variables on the stack

 include/linux/bpf_verifier.h |   1 +
 kernel/bpf/verifier.c        | 230 +++++++++++++++++------------------
 2 files changed, 113 insertions(+), 118 deletions(-)

-- 
2.47.1