bpf: Reserve space for BPF trampoline in BPF programs (9fd4a39d) · Commits · 戴 / test

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@kernel.org> Signed-off-by:

Daniel Borkmann <daniel@iogearbox.net> Acked-by:

Andrii Nakryiko <andriin@fb.com> Acked-by:

Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20191114185720.1641606-14-ast@kernel.org

arch/x86/net/bpf_jit_comp.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -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 */

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