linux-kernel - [PATCH v2 3/5] x86/bpf: Move epilogue generation to a dedicated function

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Date:   Fri, 14 Jun 2019 12:56:42 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org, Alexei Starovoitov <ast@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
        Song Liu <songliubraving@...com>,
        Kairui Song <kasong@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        David Laight <David.Laight@...LAB.COM>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>
Subject: [PATCH v2 3/5] x86/bpf: Move epilogue generation to a dedicated function

Improve code readability by moving the BPF JIT function epilogue
generation code to a dedicated emit_epilogue() function, analagous to
the existing emit_prologue() function.

Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/net/bpf_jit_comp.c | 37 ++++++++++++++++++++++++-------------
 1 file changed, 24 insertions(+), 13 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 32bfab4e21eb..da8c988b0f0f 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -240,6 +240,28 @@ static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf)
 	*pprog = prog;
 }
 
+static void emit_epilogue(u8 **pprog)
+{
+	u8 *prog = *pprog;
+	int cnt = 0;
+
+	/* mov rbx, qword ptr [rbp+0] */
+	EMIT4(0x48, 0x8B, 0x5D, 0);
+	/* mov r13, qword ptr [rbp+8] */
+	EMIT4(0x4C, 0x8B, 0x6D, 8);
+	/* mov r14, qword ptr [rbp+16] */
+	EMIT4(0x4C, 0x8B, 0x75, 16);
+	/* mov r15, qword ptr [rbp+24] */
+	EMIT4(0x4C, 0x8B, 0x7D, 24);
+
+	/* add rbp, AUX_STACK_SPACE */
+	EMIT4(0x48, 0x83, 0xC5, AUX_STACK_SPACE);
+	EMIT1(0xC9); /* leave */
+	EMIT1(0xC3); /* ret */
+
+	*pprog = prog;
+}
+
 /*
  * Generate the following code:
  *
@@ -1036,19 +1058,8 @@ xadd:			if (is_imm8(insn->off))
 			seen_exit = true;
 			/* Update cleanup_addr */
 			ctx->cleanup_addr = proglen;
-			/* mov rbx, qword ptr [rbp+0] */
-			EMIT4(0x48, 0x8B, 0x5D, 0);
-			/* mov r13, qword ptr [rbp+8] */
-			EMIT4(0x4C, 0x8B, 0x6D, 8);
-			/* mov r14, qword ptr [rbp+16] */
-			EMIT4(0x4C, 0x8B, 0x75, 16);
-			/* mov r15, qword ptr [rbp+24] */
-			EMIT4(0x4C, 0x8B, 0x7D, 24);
-
-			/* add rbp, AUX_STACK_SPACE */
-			EMIT4(0x48, 0x83, 0xC5, AUX_STACK_SPACE);
-			EMIT1(0xC9); /* leave */
-			EMIT1(0xC3); /* ret */
+
+			emit_epilogue(&prog);
 			break;
 
 		default:
-- 
2.20.1