BPF trampoline can be made to work with existing 5 bytes of BPF program
prologue, but let's add 5 bytes of NOPs to the beginning of every JITed BPF
program to make BPF trampoline job easier. They can be removed in the future.
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Acked-by: Andrii Nakryiko <andriin@xxxxxx>
---
arch/x86/net/bpf_jit_comp.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 9ccf7cd51a21..3123d4ddc6ca 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -206,7 +206,7 @@ struct jit_context {
/* number of bytes emit_call() needs to generate call instruction */
#define X86_CALL_SIZE 5
-#define PROLOGUE_SIZE 20
+#define PROLOGUE_SIZE 25
/*
* Emit x86-64 prologue code for BPF program and check its size.
@@ -215,8 +215,13 @@ struct jit_context {
static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf)
{
u8 *prog = *pprog;
- int cnt = 0;
+ int cnt = X86_CALL_SIZE;
+ /* BPF trampoline can be made to work without these nops,
+ * but let's waste 5 bytes for now and optimize later
+ */
+ memcpy(prog, ideal_nops[NOP_ATOMIC5], cnt);
+ prog += cnt;
EMIT1(0x55); /* push rbp */
EMIT3(0x48, 0x89, 0xE5); /* mov rbp, rsp */
/* sub rsp, rounded_stack_depth */
--
2.23.0
