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bpf: Inline bpf_iter_num_destroy() as a no-op

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Once destroy() returns the stack slot is no longer tracked as iterator
state, so zeroing it is dead work. Make the kfunc a no-op and inline the
call to a single BPF_JA 0 (the fixup can't drop the instruction outright,
so emit a nop; the JITs elide it).

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260804134601.2305303-5-puranjay@kernel.org
This commit is contained in:
Puranjay Mohan
2026-08-04 06:45:56 -07:00
committed by Andrii Nakryiko
parent e933477048
commit 39f047682f
2 changed files with 5 additions and 3 deletions
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4
kernel/bpf/bpf_iter.c
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@@ -818,9 +818,7 @@ __bpf_kfunc int *bpf_iter_num_next(struct bpf_iter_num* it)
__bpf_kfunc void bpf_iter_num_destroy(struct bpf_iter_num *it)
{
struct bpf_iter_num_kern *s = (void *)it;
s->cur = s->end = 0;
/* no-op */
}
__bpf_kfunc_end_defs();

4
kernel/bpf/verifier.c
View File

@@ -20047,6 +20047,10 @@ int bpf_fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
insn_buf[i++] = BPF_ST_MEM(BPF_DW, BPF_REG_1, 0, 0);
insn_buf[i++] = BPF_MOV64_IMM(BPF_REG_0, 0);
*cnt = i;
} else if (desc->func_id == special_kfunc_list[KF_bpf_iter_num_destroy]) {
/* bpf_iter_num_destroy() is a no-op; emit a nop to drop the call */
insn_buf[0] = BPF_JMP_A(0);
*cnt = 1;
}
if (env->insn_aux_data[insn_idx].arg_prog) {