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From: Brendan Jackman <jackmanb@google.com>
To: bpf@vger.kernel.org
Cc: "Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Andrii Nakryiko" <andrii.nakryiko@gmail.com>,
	"KP Singh" <kpsingh@chromium.org>,
	"Florent Revest" <revest@chromium.org>,
	linux-kernel@vger.kernel.org,
	"Björn Töpel" <bjorn.topel@gmail.com>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"Yonghong Song" <yhs@fb.com>,
	"Brendan Jackman" <jackmanb@google.com>
Subject: [PATCH bpf-next v7 02/11] bpf: x86: Factor out emission of REX byte
Date: Thu, 14 Jan 2021 18:17:42 +0000
Message-ID: <20210114181751.768687-3-jackmanb@google.com> (raw)
In-Reply-To: <20210114181751.768687-1-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>
Acked-by: John Fastabend <john.fastabend@gmail.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 30526776fa78..f15c93275a18 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -702,6 +702,21 @@ static void emit_insn_suffix(u8 **pprog, u32 ptr_reg, u32 val_reg, int off)
 	*pprog = prog;
 }
 
+/*
+ * Emit a REX byte if it will be necessary to address these registers
+ */
+static void maybe_emit_mod(u8 **pprog, u32 dst_reg, u32 src_reg, bool is64)
+{
+	u8 *prog = *pprog;
+	int cnt = 0;
+
+	if (is64)
+		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));
+	*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_mod(&prog, dst_reg, src_reg,
+				       BPF_CLASS(insn->code) == BPF_ALU64);
 			EMIT2(b2, add_2reg(0xC0, dst_reg, src_reg));
 			break;
 
@@ -1302,20 +1315,16 @@ st:			if (is_imm8(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_mod(&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_mod(&prog, dst_reg, src_reg,
+				       BPF_CLASS(insn->code) == BPF_JMP);
 			EMIT2(0x85, add_2reg(0xC0, dst_reg, src_reg));
 			goto emit_cond_jmp;
 
@@ -1351,10 +1360,8 @@ st:			if (is_imm8(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_mod(&prog, dst_reg, dst_reg,
+					       BPF_CLASS(insn->code) == BPF_JMP);
 				EMIT2(0x85, add_2reg(0xC0, dst_reg, dst_reg));
 				goto emit_cond_jmp;
 			}
-- 
2.30.0.284.gd98b1dd5eaa7-goog


  parent reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-14 18:17 [PATCH bpf-next v7 00/11] Atomics for eBPF Brendan Jackman
2021-01-14 18:17 ` [PATCH bpf-next v7 01/11] bpf: x86: Factor out emission of ModR/M for *(reg + off) Brendan Jackman
2021-01-14 18:17 ` Brendan Jackman [this message]
2021-01-14 18:17 ` [PATCH bpf-next v7 03/11] bpf: x86: Factor out a lookup table for some ALU opcodes Brendan Jackman
2021-01-14 18:17 ` [PATCH bpf-next v7 04/11] bpf: Rename BPF_XADD and prepare to encode other atomics in .imm Brendan Jackman
2021-01-14 18:17 ` [PATCH bpf-next v7 05/11] bpf: Move BPF_STX reserved field check into BPF_STX verifier code Brendan Jackman
2021-01-14 18:17 ` [PATCH bpf-next v7 06/11] bpf: Add BPF_FETCH field / create atomic_fetch_add instruction Brendan Jackman
2021-01-14 18:17 ` [PATCH bpf-next v7 07/11] bpf: Add instructions for atomic_[cmp]xchg Brendan Jackman
2021-01-14 18:17 ` [PATCH bpf-next v7 08/11] bpf: Pull out a macro for interpreting atomic ALU operations Brendan Jackman
2021-01-14 18:17 ` [PATCH bpf-next v7 09/11] bpf: Add bitwise atomic instructions Brendan Jackman
2021-01-14 18:17 ` [PATCH bpf-next v7 10/11] bpf: Add tests for new BPF atomic operations Brendan Jackman
2021-01-14 18:17 ` [PATCH bpf-next v7 11/11] bpf: Document new atomic instructions Brendan Jackman
2021-01-15  3:20 ` [PATCH bpf-next v7 00/11] Atomics for eBPF patchwork-bot+netdevbpf
2021-01-15  3:23 ` Alexei Starovoitov

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