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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,
	Brendan Jackman <jackmanb@google.com>,
	John Fastabend <john.fastabend@gmail.com>
Subject: [PATCH bpf-next v5 01/11] bpf: x86: Factor out emission of ModR/M for *(reg + off)
Date: Tue, 15 Dec 2020 12:18:05 +0000
Message-ID: <20201215121816.1048557-2-jackmanb@google.com> (raw)
In-Reply-To: <20201215121816.1048557-1-jackmanb@google.com>

The case for JITing atomics is about to get more complicated. Let's
factor out some common code to make the review and result more
readable.

NB the atomics code doesn't yet use the new helper - a subsequent
patch will add its use as a side-effect of other changes.

Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 arch/x86/net/bpf_jit_comp.c | 43 +++++++++++++++++++++----------------
 1 file changed, 25 insertions(+), 18 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 796506dcfc42..30526776fa78 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -681,6 +681,27 @@ static void emit_mov_reg(u8 **pprog, bool is64, u32 dst_reg, u32 src_reg)
 	*pprog = prog;
 }
 
+/* Emit the suffix (ModR/M etc) for addressing *(ptr_reg + off) and val_reg */
+static void emit_insn_suffix(u8 **pprog, u32 ptr_reg, u32 val_reg, int off)
+{
+	u8 *prog = *pprog;
+	int cnt = 0;
+
+	if (is_imm8(off)) {
+		/* 1-byte signed displacement.
+		 *
+		 * If off == 0 we could skip this and save one extra byte, but
+		 * special case of x86 R13 which always needs an offset is not
+		 * worth the hassle
+		 */
+		EMIT2(add_2reg(0x40, ptr_reg, val_reg), off);
+	} else {
+		/* 4-byte signed displacement */
+		EMIT1_off32(add_2reg(0x80, ptr_reg, val_reg), off);
+	}
+	*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)
 {
@@ -708,15 +729,7 @@ static void emit_ldx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
 		EMIT2(add_2mod(0x48, src_reg, dst_reg), 0x8B);
 		break;
 	}
-	/*
-	 * If insn->off == 0 we can save one extra byte, but
-	 * special case of x86 R13 which always needs an offset
-	 * is not worth the hassle
-	 */
-	if (is_imm8(off))
-		EMIT2(add_2reg(0x40, src_reg, dst_reg), off);
-	else
-		EMIT1_off32(add_2reg(0x80, src_reg, dst_reg), off);
+	emit_insn_suffix(&prog, src_reg, dst_reg, off);
 	*pprog = prog;
 }
 
@@ -751,10 +764,7 @@ static void emit_stx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
 		EMIT2(add_2mod(0x48, dst_reg, src_reg), 0x89);
 		break;
 	}
-	if (is_imm8(off))
-		EMIT2(add_2reg(0x40, dst_reg, src_reg), off);
-	else
-		EMIT1_off32(add_2reg(0x80, dst_reg, src_reg), off);
+	emit_insn_suffix(&prog, dst_reg, src_reg, off);
 	*pprog = prog;
 }
 
@@ -1240,11 +1250,8 @@ st:			if (is_imm8(insn->off))
 			goto xadd;
 		case BPF_STX | BPF_XADD | BPF_DW:
 			EMIT3(0xF0, add_2mod(0x48, dst_reg, src_reg), 0x01);
-xadd:			if (is_imm8(insn->off))
-				EMIT2(add_2reg(0x40, dst_reg, src_reg), insn->off);
-			else
-				EMIT1_off32(add_2reg(0x80, dst_reg, src_reg),
-					    insn->off);
+xadd:
+			emit_modrm_dstoff(&prog, dst_reg, src_reg, insn->off);
 			break;
 
 			/* call */
-- 
2.29.2.684.gfbc64c5ab5-goog


  reply index

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-15 12:18 [PATCH bpf-next v4 00/11] Atomics for eBPF Brendan Jackman
2020-12-15 12:18 ` Brendan Jackman [this message]
2020-12-15 12:18 ` [PATCH bpf-next v2] libbpf: Expose libbpf ringbufer epoll_fd Brendan Jackman
2020-12-15 18:35   ` Andrii Nakryiko
2020-12-15 12:18 ` [PATCH bpf-next v5 02/11] bpf: x86: Factor out emission of REX byte Brendan Jackman
2020-12-15 12:18 ` [PATCH bpf-next v5 03/11] bpf: x86: Factor out a lookup table for some ALU opcodes Brendan Jackman
2020-12-15 12:18 ` [PATCH bpf-next v5 04/11] bpf: Rename BPF_XADD and prepare to encode other atomics in .imm Brendan Jackman
2020-12-15 14:05   ` Björn Töpel
2020-12-15 12:18 ` [PATCH bpf-next v5 05/11] bpf: Move BPF_STX reserved field check into BPF_STX verifier code Brendan Jackman
2020-12-15 12:18 ` [PATCH bpf-next v5 06/11] bpf: Add BPF_FETCH field / create atomic_fetch_add instruction Brendan Jackman
2020-12-15 12:18 ` [PATCH bpf-next v5 07/11] bpf: Add instructions for atomic_[cmp]xchg Brendan Jackman
2020-12-16  6:47   ` Yonghong Song
2020-12-15 12:18 ` [PATCH bpf-next v5 08/11] bpf: Pull out a macro for interpreting atomic ALU operations Brendan Jackman
2020-12-15 12:18 ` [PATCH bpf-next v5 09/11] bpf: Add bitwise atomic instructions Brendan Jackman
2020-12-16  6:53   ` Yonghong Song
2020-12-15 12:18 ` [PATCH bpf-next v5 10/11] bpf: Add tests for new BPF atomic operations Brendan Jackman
2020-12-15 12:18 ` [PATCH bpf-next v5 11/11] bpf: Document new atomic instructions Brendan Jackman
2020-12-16  7:08   ` Yonghong Song
2020-12-16 11:44     ` Brendan Jackman
2020-12-16 15:25       ` Yonghong Song

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