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x86: bpf_jit: small optimization in emit_bpf_tail_call()
Saves 4 bytes replacing following instructions : lea rax, [rsi + rdx * 8 + offsetof(...)] mov rax, qword ptr [rax] cmp rax, 0 by : mov rax, [rsi + rdx * 8 + offsetof(...)] test rax, rax Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Alexei Starovoitov <ast@kernel.org> Cc: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
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1 changed files with 4 additions and 5 deletions
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@ -287,7 +287,7 @@ static void emit_bpf_tail_call(u8 **pprog)
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EMIT4(0x48, 0x8B, 0x46, /* mov rax, qword ptr [rsi + 16] */
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offsetof(struct bpf_array, map.max_entries));
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EMIT3(0x48, 0x39, 0xD0); /* cmp rax, rdx */
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#define OFFSET1 47 /* number of bytes to jump */
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#define OFFSET1 43 /* number of bytes to jump */
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EMIT2(X86_JBE, OFFSET1); /* jbe out */
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label1 = cnt;
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@ -296,21 +296,20 @@ static void emit_bpf_tail_call(u8 **pprog)
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*/
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EMIT2_off32(0x8B, 0x85, 36); /* mov eax, dword ptr [rbp + 36] */
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EMIT3(0x83, 0xF8, MAX_TAIL_CALL_CNT); /* cmp eax, MAX_TAIL_CALL_CNT */
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#define OFFSET2 36
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#define OFFSET2 32
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EMIT2(X86_JA, OFFSET2); /* ja out */
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label2 = cnt;
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EMIT3(0x83, 0xC0, 0x01); /* add eax, 1 */
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EMIT2_off32(0x89, 0x85, 36); /* mov dword ptr [rbp + 36], eax */
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/* prog = array->ptrs[index]; */
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EMIT4_off32(0x48, 0x8D, 0x84, 0xD6, /* lea rax, [rsi + rdx * 8 + offsetof(...)] */
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EMIT4_off32(0x48, 0x8B, 0x84, 0xD6, /* mov rax, [rsi + rdx * 8 + offsetof(...)] */
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offsetof(struct bpf_array, ptrs));
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EMIT3(0x48, 0x8B, 0x00); /* mov rax, qword ptr [rax] */
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/* if (prog == NULL)
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* goto out;
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*/
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EMIT4(0x48, 0x83, 0xF8, 0x00); /* cmp rax, 0 */
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EMIT3(0x48, 0x85, 0xC0); /* test rax,rax */
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#define OFFSET3 10
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EMIT2(X86_JE, OFFSET3); /* je out */
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label3 = cnt;
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