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From: Brendan Jackman <jackmanb@google.com>
To: bpf@vger.kernel.org
Cc: Alexei Starovoitov <ast@kernel.org>, Yonghong Song <yhs@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	KP Singh <kpsingh@chromium.org>,
	Florent Revest <revest@chromium.org>,
	Brendan Jackman <jackmanb@google.com>
Subject: [PATCH 2/7] bpf: x86: Factor out emission of REX byte
Date: Mon, 23 Nov 2020 17:31:57 +0000	[thread overview]
Message-ID: <20201123173202.1335708-3-jackmanb@google.com> (raw)
In-Reply-To: <20201123173202.1335708-1-jackmanb@google.com>

The JIT case for encoding atomic ops is about to get more
complicated. In order to make the review & resulting code easier,
let's factor out some shared helpers.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 arch/x86/net/bpf_jit_comp.c | 39 ++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 94b17bd30e00..a839c1a54276 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -702,6 +702,21 @@ static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off)
 	*pprog = prog;
 }
 
+/*
+ * Emit a REX byte if it will be necessary to address these registers
+ */
+static void maybe_emit_rex(u8 **pprog, u32 reg_rm, u32 reg_reg, bool wide)
+{
+	u8 *prog = *pprog;
+	int cnt = 0;
+
+	if (wide)
+		EMIT1(add_2mod(0x48, reg_rm, reg_reg));
+	else if (is_ereg(reg_rm) || is_ereg(reg_reg))
+		EMIT1(add_2mod(0x40, reg_rm, reg_reg));
+	*pprog = prog;
+}
+
 /* LDX: dst_reg = *(u8*)(src_reg + off) */
 static void emit_ldx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
 {
@@ -854,10 +869,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 			case BPF_OR: b2 = 0x09; break;
 			case BPF_XOR: b2 = 0x31; break;
 			}
-			if (BPF_CLASS(insn->code) == BPF_ALU64)
-				EMIT1(add_2mod(0x48, dst_reg, src_reg));
-			else if (is_ereg(dst_reg) || is_ereg(src_reg))
-				EMIT1(add_2mod(0x40, dst_reg, src_reg));
+			maybe_emit_rex(&prog, dst_reg, src_reg,
+				       BPF_CLASS(insn->code) == BPF_ALU64);
 			EMIT2(b2, add_2reg(0xC0, dst_reg, src_reg));
 			break;
 
@@ -1301,20 +1314,16 @@ xadd:			emit_modrm_dstoff(&prog, dst_reg, src_reg, insn->off);
 		case BPF_JMP32 | BPF_JSGE | BPF_X:
 		case BPF_JMP32 | BPF_JSLE | BPF_X:
 			/* cmp dst_reg, src_reg */
-			if (BPF_CLASS(insn->code) == BPF_JMP)
-				EMIT1(add_2mod(0x48, dst_reg, src_reg));
-			else if (is_ereg(dst_reg) || is_ereg(src_reg))
-				EMIT1(add_2mod(0x40, dst_reg, src_reg));
+			maybe_emit_rex(&prog, dst_reg, src_reg,
+				       BPF_CLASS(insn->code) == BPF_JMP);
 			EMIT2(0x39, add_2reg(0xC0, dst_reg, src_reg));
 			goto emit_cond_jmp;
 
 		case BPF_JMP | BPF_JSET | BPF_X:
 		case BPF_JMP32 | BPF_JSET | BPF_X:
 			/* test dst_reg, src_reg */
-			if (BPF_CLASS(insn->code) == BPF_JMP)
-				EMIT1(add_2mod(0x48, dst_reg, src_reg));
-			else if (is_ereg(dst_reg) || is_ereg(src_reg))
-				EMIT1(add_2mod(0x40, dst_reg, src_reg));
+			maybe_emit_rex(&prog, dst_reg, src_reg,
+				       BPF_CLASS(insn->code) == BPF_JMP);
 			EMIT2(0x85, add_2reg(0xC0, dst_reg, src_reg));
 			goto emit_cond_jmp;
 
@@ -1350,10 +1359,8 @@ xadd:			emit_modrm_dstoff(&prog, dst_reg, src_reg, insn->off);
 		case BPF_JMP32 | BPF_JSLE | BPF_K:
 			/* test dst_reg, dst_reg to save one extra byte */
 			if (imm32 == 0) {
-				if (BPF_CLASS(insn->code) == BPF_JMP)
-					EMIT1(add_2mod(0x48, dst_reg, dst_reg));
-				else if (is_ereg(dst_reg))
-					EMIT1(add_2mod(0x40, dst_reg, dst_reg));
+				maybe_emit_rex(&prog, dst_reg, dst_reg,
+					       BPF_CLASS(insn->code) == BPF_JMP);
 				EMIT2(0x85, add_2reg(0xC0, dst_reg, dst_reg));
 				goto emit_cond_jmp;
 			}
-- 
2.29.2.454.gaff20da3a2-goog


  parent reply	other threads:[~2020-11-23 17:32 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-23 17:31 [PATCH 0/7] Atomics for eBPF Brendan Jackman
2020-11-23 17:31 ` [PATCH 1/7] bpf: Factor out emission of ModR/M for *(reg + off) Brendan Jackman
2020-11-23 17:31 ` Brendan Jackman [this message]
2020-11-23 17:31 ` [PATCH 3/7] bpf: Rename BPF_XADD and prepare to encode other atomics in .imm Brendan Jackman
2020-11-23 23:54   ` Yonghong Song
2020-11-24 11:02     ` Brendan Jackman
2020-11-24 16:04       ` Yonghong Song
2020-11-24  3:28   ` kernel test robot
2020-11-24  3:28     ` kernel test robot
2020-11-24  6:50   ` Alexei Starovoitov
2020-11-24 11:21     ` Brendan Jackman
2020-11-24 22:43       ` Alexei Starovoitov
2020-11-23 17:31 ` [PATCH 4/7] bpf: Move BPF_STX reserved field check into BPF_STX verifier code Brendan Jackman
2020-11-23 17:32 ` [PATCH 5/7] bpf: Add BPF_FETCH field / create atomic_fetch_add instruction Brendan Jackman
2020-11-23 21:12   ` kernel test robot
2020-11-23 21:12     ` kernel test robot
2020-11-23 21:51   ` kernel test robot
2020-11-23 21:51     ` kernel test robot
2020-11-24  6:52   ` Alexei Starovoitov
2020-11-24 10:48     ` Brendan Jackman
2020-11-23 17:32 ` [PATCH 6/7] bpf: Add instructions for atomic_cmpxchg and friends Brendan Jackman
2020-11-23 19:29   ` Brendan Jackman
2020-11-24  6:40   ` Alexei Starovoitov
2020-11-24 10:55     ` Brendan Jackman
2020-11-24 22:51       ` Alexei Starovoitov
2020-11-23 17:32 ` [PATCH 7/7] bpf: Add tests for new BPF atomic operations Brendan Jackman
2020-11-24  0:26   ` Yonghong Song
2020-11-24 13:10     ` Brendan Jackman
2020-11-23 17:36 ` [PATCH 0/7] Atomics for eBPF Brendan Jackman

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