diff options
author | Daniel Borkmann <daniel@iogearbox.net> | 2018-02-24 03:08:02 +0300 |
---|---|---|
committer | Alexei Starovoitov <ast@kernel.org> | 2018-02-24 09:50:00 +0300 |
commit | 0869175220b339b81de48872c8198c3ed75782e3 (patch) | |
tree | fabeb650153a6cc3c2bc1fdefbe47f44cebf56e2 /arch/x86 | |
parent | 4c38e2f386b4fc5fd95d1203c74819948e2e903d (diff) | |
download | linux-0869175220b339b81de48872c8198c3ed75782e3.tar.xz |
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>
Diffstat (limited to 'arch/x86')
-rw-r--r-- | arch/x86/net/bpf_jit_comp.c | 28 |
1 files changed, 16 insertions, 12 deletions
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 5b8fc1326aa1..70f9748da7aa 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -216,7 +216,7 @@ struct jit_context { /* emit x64 prologue code for BPF program and check it's size. * bpf_tail_call helper will skip it while jumping into another program */ -static void emit_prologue(u8 **pprog, u32 stack_depth) +static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf) { u8 *prog = *pprog; int cnt = 0; @@ -251,18 +251,21 @@ static void emit_prologue(u8 **pprog, u32 stack_depth) /* mov qword ptr [rbp+24],r15 */ EMIT4(0x4C, 0x89, 0x7D, 24); - /* Clear the tail call counter (tail_call_cnt): for eBPF tail calls - * we need to reset the counter to 0. It's done in two instructions, - * resetting rax register to 0 (xor on eax gets 0 extended), and - * moving it to the counter location. - */ + if (!ebpf_from_cbpf) { + /* Clear the tail call counter (tail_call_cnt): for eBPF tail + * calls we need to reset the counter to 0. It's done in two + * instructions, resetting rax register to 0, and moving it + * to the counter location. + */ - /* xor eax, eax */ - EMIT2(0x31, 0xc0); - /* mov qword ptr [rbp+32], rax */ - EMIT4(0x48, 0x89, 0x45, 32); + /* xor eax, eax */ + EMIT2(0x31, 0xc0); + /* mov qword ptr [rbp+32], rax */ + EMIT4(0x48, 0x89, 0x45, 32); + + BUILD_BUG_ON(cnt != PROLOGUE_SIZE); + } - BUILD_BUG_ON(cnt != PROLOGUE_SIZE); *pprog = prog; } @@ -453,7 +456,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, int proglen = 0; u8 *prog = temp; - emit_prologue(&prog, bpf_prog->aux->stack_depth); + emit_prologue(&prog, bpf_prog->aux->stack_depth, + bpf_prog_was_classic(bpf_prog)); if (seen_ld_abs) emit_load_skb_data_hlen(&prog); |