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authorDaniel Borkmann <daniel@iogearbox.net>2018-02-24 01:08:02 +0100
committerAlexei Starovoitov <ast@kernel.org>2018-02-23 22:50:00 -0800
commit0869175220b339b81de48872c8198c3ed75782e3 (patch)
treefabeb650153a6cc3c2bc1fdefbe47f44cebf56e2 /arch/x86/net
parent4c38e2f386b4fc5fd95d1203c74819948e2e903d (diff)
downloadlinux-0869175220b339b81de48872c8198c3ed75782e3.tar.bz2
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/net')
-rw-r--r--arch/x86/net/bpf_jit_comp.c28
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);