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bpf, x64: save 5 bytes in prologue when ebpf insns came from cbpf
While it's rather cumbersome to reduce prologue for cBPF->eBPF migrations wrt spill/fill for r15 which is callee saved register due to bpf_error path in bpf_jit.S that is both used by migrations as well as native eBPF, we can still trivially save 5 bytes in prologue for the former since tail calls can never be used there. cBPF->eBPF migrations also have their own custom prologue in BPF asm that xors A and X reg anyway, so it's fine we skip this here. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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@ -216,7 +216,7 @@ struct jit_context {
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/* emit x64 prologue code for BPF program and check it's size.
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* bpf_tail_call helper will skip it while jumping into another program
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*/
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static void emit_prologue(u8 **pprog, u32 stack_depth)
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static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf)
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{
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u8 *prog = *pprog;
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int cnt = 0;
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@ -251,18 +251,21 @@ static void emit_prologue(u8 **pprog, u32 stack_depth)
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/* mov qword ptr [rbp+24],r15 */
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EMIT4(0x4C, 0x89, 0x7D, 24);
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/* Clear the tail call counter (tail_call_cnt): for eBPF tail calls
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* we need to reset the counter to 0. It's done in two instructions,
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* resetting rax register to 0 (xor on eax gets 0 extended), and
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* moving it to the counter location.
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*/
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if (!ebpf_from_cbpf) {
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/* Clear the tail call counter (tail_call_cnt): for eBPF tail
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* calls we need to reset the counter to 0. It's done in two
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* instructions, resetting rax register to 0, and moving it
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* to the counter location.
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*/
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/* xor eax, eax */
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EMIT2(0x31, 0xc0);
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/* mov qword ptr [rbp+32], rax */
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EMIT4(0x48, 0x89, 0x45, 32);
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/* xor eax, eax */
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EMIT2(0x31, 0xc0);
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/* mov qword ptr [rbp+32], rax */
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EMIT4(0x48, 0x89, 0x45, 32);
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BUILD_BUG_ON(cnt != PROLOGUE_SIZE);
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}
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BUILD_BUG_ON(cnt != PROLOGUE_SIZE);
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*pprog = prog;
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}
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@ -453,7 +456,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
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int proglen = 0;
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u8 *prog = temp;
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emit_prologue(&prog, bpf_prog->aux->stack_depth);
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emit_prologue(&prog, bpf_prog->aux->stack_depth,
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bpf_prog_was_classic(bpf_prog));
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if (seen_ld_abs)
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emit_load_skb_data_hlen(&prog);
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