Commit 08691752 authored by Daniel Borkmann's avatar Daniel Borkmann Committed by Alexei Starovoitov

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: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 4c38e2f3
......@@ -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);
......
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