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From:   Luke Nelson <lukenels@cs.washington.edu>
To:     bpf@vger.kernel.org
Cc:     Luke Nelson <luke.r.nels@gmail.com>,
        =?UTF-8?q?Bj=C3=B6rn=20T=C3=B6pel?= <bjorn.topel@gmail.com>,
        Xi Wang <xi.wang@gmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        Andrii Nakryiko <andriin@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@chromium.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>, netdev@vger.kernel.org,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: [RFC PATCH bpf-next 2/3] bpf, riscv: Add encodings for compressed instructions
Date:   Mon, 13 Jul 2020 11:37:10 -0700
Message-Id: <20200713183711.762244-3-luke.r.nels@gmail.com>
In-Reply-To: <20200713183711.762244-1-luke.r.nels@gmail.com>
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This patch adds functions for encoding and emitting compressed riscv
(RVC) instructions to the BPF JIT.

Some regular riscv instructions can be compressed into an RVC instruction
if the instruction fields meet some requirements. For example, "add rd,
rs1, rs2" can be compressed into "c.add rd, rs2" when rd == rs1.

To make using RVC encodings simpler, this patch also adds helper
functions that selectively emit either a regular instruction or a
compressed instruction if possible.

For example, emit_add will produce a "c.add" if possible and regular
"add" otherwise.

Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
---
 arch/riscv/net/bpf_jit.h | 474 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 474 insertions(+)

diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h
index 5c89ea904c1a..f3ac2d4a50f7 100644
--- a/arch/riscv/net/bpf_jit.h
+++ b/arch/riscv/net/bpf_jit.h
@@ -13,6 +13,15 @@
 #include <linux/filter.h>
 #include <asm/cacheflush.h>
 
+static inline bool rvc_enabled(void)
+{
+#ifdef CONFIG_RISCV_ISA_C
+	return true;
+#else
+	return false;
+#endif
+}
+
 enum {
 	RV_REG_ZERO =	0,	/* The constant value 0 */
 	RV_REG_RA =	1,	/* Return address */
@@ -48,6 +57,18 @@ enum {
 	RV_REG_T6 =	31,
 };
 
+static inline bool is_creg(u8 reg)
+{
+	return (1 << reg) & (BIT(RV_REG_FP) |
+			     BIT(RV_REG_S1) |
+			     BIT(RV_REG_A0) |
+			     BIT(RV_REG_A1) |
+			     BIT(RV_REG_A2) |
+			     BIT(RV_REG_A3) |
+			     BIT(RV_REG_A4) |
+			     BIT(RV_REG_A5));
+}
+
 struct rv_jit_context {
 	struct bpf_prog *prog;
 	u16 *insns;		/* RV insns */
@@ -134,6 +155,16 @@ static inline int invert_bpf_cond(u8 cond)
 	return -1;
 }
 
+static inline bool is_6b_int(long val)
+{
+	return -(1L << 5) <= val && val < (1L << 5);
+}
+
+static inline bool is_10b_int(long val)
+{
+	return -(1L << 9) <= val && val < (1L << 9);
+}
+
 static inline bool is_12b_int(long val)
 {
 	return -(1L << 11) <= val && val < (1L << 11);
@@ -224,6 +255,59 @@ static inline u32 rv_amo_insn(u8 funct5, u8 aq, u8 rl, u8 rs2, u8 rs1,
 	return rv_r_insn(funct7, rs2, rs1, funct3, rd, opcode);
 }
 
+/* RISC-V compressed instruction formats. */
+
+static inline u32 rv_cr_insn(u8 funct4, u8 rd, u8 rs2, u8 op)
+{
+	return (funct4 << 12) | (rd << 7) | (rs2 << 2) | op;
+}
+
+static inline u32 rv_ci_insn(u8 funct3, u32 imm6, u8 rd, u8 op)
+{
+	u16 imm;
+
+	imm = ((imm6 & 0x20) << 7) | ((imm6 & 0x1f) << 2);
+	return (funct3 << 13) | (rd << 7) | op | imm;
+}
+
+static inline u32 rv_css_insn(u8 funct3, u32 uimm, u8 rs2, u8 op)
+{
+	return (funct3 << 13) | (uimm << 7) | (rs2 << 2) | op;
+}
+
+static inline u32 rv_ciw_insn(u8 funct3, u32 uimm, u8 rd, u8 op)
+{
+	return (funct3 << 13) | (uimm << 5) | ((rd & 0x7) << 2) | op;
+}
+
+static inline u32 rv_cl_insn(u8 funct3, u32 imm_hi, u8 rs1, u32 imm_lo, u8 rd,
+			     u8 op)
+{
+	return (funct3 << 13) | (imm_hi << 10) | ((rs1 & 0x7) << 7) |
+		(imm_lo << 5) | ((rd & 0x7) << 2) | op;
+}
+
+static inline u32 rv_cs_insn(u8 funct3, u32 imm_hi, u8 rs1, u32 imm_lo, u8 rs2,
+			     u8 op)
+{
+	return (funct3 << 13) | (imm_hi << 10) | ((rs1 & 0x7) << 7) |
+		(imm_lo << 5) | ((rs2 & 0x7) << 2) | op;
+}
+
+static inline u32 rv_ca_insn(u8 funct6, u8 rd, u8 funct2, u8 rs2, u8 op)
+{
+	return (funct6 << 10) | ((rd & 0x7) << 7) | (funct2 << 5) |
+		((rs2 & 0x7) << 2) | op;
+}
+
+static inline u32 rv_cb_insn(u8 funct3, u32 imm6, u8 funct2, u8 rd, u8 op)
+{
+	u16 imm;
+
+	imm = ((imm6 & 0x20) << 7) | ((imm6 & 0x1f) << 2);
+	return (funct3 << 13) | (funct2 << 10) | ((rd & 0x7) << 7) | op | imm;
+}
+
 /* Instructions shared by both RV32 and RV64. */
 
 static inline u32 rv_addi(u8 rd, u8 rs1, u16 imm11_0)
@@ -431,6 +515,135 @@ static inline u32 rv_amoadd_w(u8 rd, u8 rs2, u8 rs1, u8 aq, u8 rl)
 	return rv_amo_insn(0, aq, rl, rs2, rs1, 2, rd, 0x2f);
 }
 
+/* RVC instrutions. */
+
+static inline u32 rvc_addi4spn(u8 rd, u32 imm10)
+{
+	u32 imm;
+
+	imm = ((imm10 & 0x30) << 2) | ((imm10 & 0x3c0) >> 4) |
+		((imm10 & 0x4) >> 1) | ((imm10 & 0x8) >> 3);
+	return rv_ciw_insn(0x0, imm, rd, 0x0);
+}
+
+static inline u32 rvc_lw(u8 rd, u32 imm7, u8 rs1)
+{
+	u32 imm_hi, imm_lo;
+
+	imm_hi = (imm7 & 0x38) >> 3;
+	imm_lo = ((imm7 & 0x4) >> 1) | ((imm7 & 0x40) >> 6);
+	return rv_cl_insn(0x2, imm_hi, rs1, imm_lo, rd, 0x0);
+}
+
+static inline u32 rvc_sw(u8 rs1, u32 imm7, u8 rs2)
+{
+	u32 imm_hi, imm_lo;
+
+	imm_hi = (imm7 & 0x38) >> 3;
+	imm_lo = ((imm7 & 0x4) >> 1) | ((imm7 & 0x40) >> 6);
+	return rv_cs_insn(0x6, imm_hi, rs1, imm_lo, rs2, 0x0);
+}
+
+static inline u32 rvc_addi(u8 rd, u8 imm6)
+{
+	return rv_ci_insn(0, imm6, rd, 0x1);
+}
+
+static inline u32 rvc_li(u8 rd, u8 imm6)
+{
+	return rv_ci_insn(0x2, imm6, rd, 0x1);
+}
+
+static inline u32 rvc_addi16sp(u32 imm10)
+{
+	u32 imm;
+
+	imm = ((imm10 & 0x200) >> 4) | (imm10 & 0x10) | ((imm10 & 0x40) >> 3) |
+		((imm10 & 0x180) >> 6) | ((imm10 & 0x20) >> 5);
+	return rv_ci_insn(0x3, imm, RV_REG_SP, 0x1);
+}
+
+static inline u32 rvc_lui(u8 rd, u8 imm6)
+{
+	return rv_ci_insn(0x3, imm6, rd, 0x1);
+}
+
+static inline u32 rvc_srli(u8 rd, u8 imm6)
+{
+	return rv_cb_insn(0x4, imm6, 0, rd, 0x1);
+}
+
+static inline u32 rvc_srai(u8 rd, u8 imm6)
+{
+	return rv_cb_insn(0x4, imm6, 0x1, rd, 0x1);
+}
+
+static inline u32 rvc_andi(u8 rd, u8 imm6)
+{
+	return rv_cb_insn(0x4, imm6, 0x2, rd, 0x1);
+}
+
+static inline u32 rvc_sub(u8 rd, u8 rs)
+{
+	return rv_ca_insn(0x23, rd, 0, rs, 0x1);
+}
+
+static inline u32 rvc_xor(u8 rd, u8 rs)
+{
+	return rv_ca_insn(0x23, rd, 0x1, rs, 0x1);
+}
+
+static inline u32 rvc_or(u8 rd, u8 rs)
+{
+	return rv_ca_insn(0x23, rd, 0x2, rs, 0x1);
+}
+
+static inline u32 rvc_and(u8 rd, u8 rs)
+{
+	return rv_ca_insn(0x23, rd, 0x3, rs, 0x1);
+}
+
+static inline u32 rvc_slli(u8 rd, u8 imm6)
+{
+	return rv_ci_insn(0, imm6, rd, 0x2);
+}
+
+static inline u32 rvc_lwsp(u8 rd, u32 imm8)
+{
+	u32 imm;
+
+	imm = ((imm8 & 0xc0) >> 6) | (imm8 & 0x3c);
+	return rv_ci_insn(0x2, imm, rd, 0x2);
+}
+
+static inline u32 rvc_jr(u8 rs1)
+{
+	return rv_cr_insn(0x8, rs1, RV_REG_ZERO, 0x2);
+}
+
+static inline u32 rvc_mv(u8 rd, u8 rs)
+{
+	return rv_cr_insn(0x8, rd, rs, 0x2);
+}
+
+static inline u32 rvc_jalr(u8 rs1)
+{
+	return rv_cr_insn(0x9, rs1, RV_REG_ZERO, 0x2);
+}
+
+static inline u32 rvc_add(u8 rd, u8 rs)
+{
+	return rv_cr_insn(0x9, rd, rs, 0x2);
+}
+
+static inline u32 rvc_swsp(u32 imm8, u8 rs2)
+{
+	u32 imm;
+
+	imm = (imm8 & 0x3c) | ((imm8 & 0xc0) >> 6);
+	return rv_css_insn(0x6, imm, rs2, 0x2);
+}
+
 /*
  * RV64-only instructions.
  *
@@ -520,6 +733,267 @@ static inline u32 rv_amoadd_d(u8 rd, u8 rs2, u8 rs1, u8 aq, u8 rl)
 	return rv_amo_insn(0, aq, rl, rs2, rs1, 3, rd, 0x2f);
 }
 
+/* RV64-only RVC instructions. */
+
+static inline u32 rvc_ld(u8 rd, u32 imm8, u8 rs1)
+{
+	u32 imm_hi, imm_lo;
+
+	imm_hi = (imm8 & 0x38) >> 3;
+	imm_lo = (imm8 & 0xc0) >> 6;
+	return rv_cl_insn(0x3, imm_hi, rs1, imm_lo, rd, 0x0);
+}
+
+static inline u32 rvc_sd(u8 rs1, u32 imm8, u8 rs2)
+{
+	u32 imm_hi, imm_lo;
+
+	imm_hi = (imm8 & 0x38) >> 3;
+	imm_lo = (imm8 & 0xc0) >> 6;
+	return rv_cs_insn(0x7, imm_hi, rs1, imm_lo, rs2, 0x0);
+}
+
+static inline u32 rvc_subw(u8 rd, u8 rs)
+{
+	return rv_ca_insn(0x27, rd, 0, rs, 0x1);
+}
+
+static inline u32 rvc_addiw(u8 rd, u8 imm6)
+{
+	return rv_ci_insn(0x1, imm6, rd, 0x1);
+}
+
+static inline u32 rvc_ldsp(u8 rd, u32 imm9)
+{
+	u32 imm;
+
+	imm = ((imm9 & 0x1c0) >> 6) | (imm9 & 0x38);
+	return rv_ci_insn(0x3, imm, rd, 0x2);
+}
+
+static inline u32 rvc_sdsp(u32 imm9, u8 rs2)
+{
+	u32 imm;
+
+	imm = (imm9 & 0x38) | ((imm9 & 0x1c0) >> 6);
+	return rv_css_insn(0x7, imm, rs2, 0x2);
+}
+
+#endif /* __riscv_xlen == 64 */
+
+/* Helper functions that emit RVC instructions when possible. */
+
+static inline void emit_jalr(u8 rd, u8 rs, s32 imm, struct rv_jit_context *ctx)
+{
+	if (rvc_enabled() && rd == RV_REG_RA && rs && !imm)
+		emitc(rvc_jalr(rs), ctx);
+	else if (rvc_enabled() && !rd && rs && !imm)
+		emitc(rvc_jr(rs), ctx);
+	else
+		emit(rv_jalr(rd, rs, imm), ctx);
+}
+
+static inline void emit_mv(u8 rd, u8 rs, struct rv_jit_context *ctx)
+{
+	if (rvc_enabled() && rd && rs)
+		emitc(rvc_mv(rd, rs), ctx);
+	else
+		emit(rv_addi(rd, rs, 0), ctx);
+}
+
+static inline void emit_add(u8 rd, u8 rs1, u8 rs2, struct rv_jit_context *ctx)
+{
+	if (rvc_enabled() && rd && rd == rs1 && rs2)
+		emitc(rvc_add(rd, rs2), ctx);
+	else
+		emit(rv_add(rd, rs1, rs2), ctx);
+}
+
+static inline void emit_addi(u8 rd, u8 rs, s32 imm, struct rv_jit_context *ctx)
+{
+	if (rd == rs && !imm)
+		/*
+		 * RVC cannot handle imm == 0. Handle it here by emitting
+		 * no instructions since it should behave as a no-op.
+		 */
+		return;
+	else if (rvc_enabled() && rd == RV_REG_SP && rd == rs &&
+		 is_10b_int(imm) && !(imm & 0xf))
+		emitc(rvc_addi16sp(imm), ctx);
+	else if (rvc_enabled() && is_creg(rd) && rs == RV_REG_SP &&
+		 (u32)imm < 0x400 && !(imm & 0x3) && imm)
+		emitc(rvc_addi4spn(rd, imm), ctx);
+	else if (rvc_enabled() && rd && rd == rs && is_6b_int(imm))
+		emitc(rvc_addi(rd, imm), ctx);
+	else
+		emit(rv_addi(rd, rs, imm), ctx);
+}
+
+static inline void emit_li(u8 rd, s32 imm, struct rv_jit_context *ctx)
+{
+	if (rvc_enabled() && rd && is_6b_int(imm))
+		emitc(rvc_li(rd, imm), ctx);
+	else
+		emit(rv_addi(rd, RV_REG_ZERO, imm), ctx);
+}
+
+static inline void emit_lui(u8 rd, s32 imm, struct rv_jit_context *ctx)
+{
+	if (rvc_enabled() && rd && rd != RV_REG_SP && is_6b_int(imm) && imm)
+		emitc(rvc_lui(rd, imm), ctx);
+	else
+		emit(rv_lui(rd, imm), ctx);
+}
+
+static inline void emit_slli(u8 rd, u8 rs, s32 imm, struct rv_jit_context *ctx)
+{
+	if (rd == rs && !imm)
+		/*
+		 * RVC cannot handle imm == 0. Handle it here by emitting
+		 * no instructions since it should behave as a no-op.
+		 */
+		return;
+	else if (rvc_enabled() && rd && rd == rs)
+		emitc(rvc_slli(rd, imm), ctx);
+	else
+		emit(rv_slli(rd, rs, imm), ctx);
+}
+
+static inline void emit_andi(u8 rd, u8 rs, s32 imm, struct rv_jit_context *ctx)
+{
+	if (rvc_enabled() && is_creg(rd) && rd == rs && is_6b_int(imm))
+		emitc(rvc_andi(rd, imm), ctx);
+	else
+		emit(rv_andi(rd, rs, imm), ctx);
+}
+
+static inline void emit_srli(u8 rd, u8 rs, s32 imm, struct rv_jit_context *ctx)
+{
+	if (rd == rs && !imm)
+		/*
+		 * RVC cannot handle imm == 0. Handle it here by emitting
+		 * no instructions since it should behave as a no-op.
+		 */
+		return;
+	else if (rvc_enabled() && is_creg(rd) && rd == rs)
+		emitc(rvc_srli(rd, imm), ctx);
+	else
+		emit(rv_srli(rd, rs, imm), ctx);
+}
+
+static inline void emit_srai(u8 rd, u8 rs, s32 imm, struct rv_jit_context *ctx)
+{
+	if (rd == rs && !imm)
+		/*
+		 * RVC cannot handle imm == 0. Handle it here by emitting
+		 * no instructions since it should behave as a no-op.
+		 */
+		return;
+	else if (rvc_enabled() && is_creg(rd) && rd == rs)
+		emitc(rvc_srai(rd, imm), ctx);
+	else
+		emit(rv_srai(rd, rs, imm), ctx);
+}
+
+static inline void emit_sub(u8 rd, u8 rs1, u8 rs2, struct rv_jit_context *ctx)
+{
+	if (rvc_enabled() && is_creg(rd) && rd == rs1 && is_creg(rs2))
+		emitc(rvc_sub(rd, rs2), ctx);
+	else
+		emit(rv_sub(rd, rs1, rs2), ctx);
+}
+
+static inline void emit_or(u8 rd, u8 rs1, u8 rs2, struct rv_jit_context *ctx)
+{
+	if (rvc_enabled() && is_creg(rd) && rd == rs1 && is_creg(rs2))
+		emitc(rvc_or(rd, rs2), ctx);
+	else
+		emit(rv_or(rd, rs1, rs2), ctx);
+}
+
+static inline void emit_and(u8 rd, u8 rs1, u8 rs2, struct rv_jit_context *ctx)
+{
+	if (rvc_enabled() && is_creg(rd) && rd == rs1 && is_creg(rs2))
+		emitc(rvc_and(rd, rs2), ctx);
+	else
+		emit(rv_and(rd, rs1, rs2), ctx);
+}
+
+static inline void emit_xor(u8 rd, u8 rs1, u8 rs2, struct rv_jit_context *ctx)
+{
+	if (rvc_enabled() && is_creg(rd) && rd == rs1 && is_creg(rs2))
+		emitc(rvc_xor(rd, rs2), ctx);
+	else
+		emit(rv_xor(rd, rs1, rs2), ctx);
+}
+
+static inline void emit_lw(u8 rd, s32 off, u8 rs1, struct rv_jit_context *ctx)
+{
+	if (rvc_enabled() && rs1 == RV_REG_SP && rd && (u32)off < 0x100 &&
+	    !(off & 0x3))
+		emitc(rvc_lwsp(rd, off), ctx);
+	else if (rvc_enabled() && is_creg(rd) && is_creg(rs1) &&
+		 (u32)off < 0x80 && !(off & 0x3))
+		emitc(rvc_lw(rd, off, rs1), ctx);
+	else
+		emit(rv_lw(rd, off, rs1), ctx);
+}
+
+static inline void emit_sw(u8 rs1, s32 off, u8 rs2, struct rv_jit_context *ctx)
+{
+	if (rvc_enabled() && rs1 == RV_REG_SP && (u32)off < 0x100 &&
+	    !(off & 0x3))
+		emitc(rvc_swsp(off, rs2), ctx);
+	else if (rvc_enabled() && is_creg(rs1) && is_creg(rs2) &&
+		 (u32)off < 0x80 && !(off & 0x3))
+		emitc(rvc_sw(rs1, off, rs2), ctx);
+	else
+		emit(rv_sw(rs1, off, rs2), ctx);
+}
+
+/* RV64-only helper functions. */
+#if __riscv_xlen == 64
+
+static inline void emit_addiw(u8 rd, u8 rs, s32 imm, struct rv_jit_context *ctx)
+{
+	if (rvc_enabled() && rd && rd == rs && is_6b_int(imm))
+		emitc(rvc_addiw(rd, imm), ctx);
+	else
+		emit(rv_addiw(rd, rs, imm), ctx);
+}
+
+static inline void emit_ld(u8 rd, s32 off, u8 rs1, struct rv_jit_context *ctx)
+{
+	if (rvc_enabled() && rs1 == RV_REG_SP && rd && (u32)off < 0x200 &&
+	    !(off & 0x7))
+		emitc(rvc_ldsp(rd, off), ctx);
+	else if (rvc_enabled() && is_creg(rd) && is_creg(rs1) &&
+		 (u32)off < 0x100 && !(off & 0x7))
+		emitc(rvc_ld(rd, off, rs1), ctx);
+	else
+		emit(rv_ld(rd, off, rs1), ctx);
+}
+
+static inline void emit_sd(u8 rs1, s32 off, u8 rs2, struct rv_jit_context *ctx)
+{
+	if (rvc_enabled() && rs1 == RV_REG_SP && (u32)off < 0x200 &&
+	    !(off & 0x7))
+		emitc(rvc_sdsp(off, rs2), ctx);
+	else if (rvc_enabled() && is_creg(rs1) && is_creg(rs2) &&
+		 (u32)off < 0x100 && !(off & 0x7))
+		emitc(rvc_sd(rs1, off, rs2), ctx);
+	else
+		emit(rv_sd(rs1, off, rs2), ctx);
+}
+
+static inline void emit_subw(u8 rd, u8 rs1, u8 rs2, struct rv_jit_context *ctx)
+{
+	if (rvc_enabled() && is_creg(rd) && rd == rs1 && is_creg(rs2))
+		emitc(rvc_subw(rd, rs2), ctx);
+	else
+		emit(rv_subw(rd, rs1, rs2), ctx);
+}
+
 #endif /* __riscv_xlen == 64 */
 
 void bpf_jit_build_prologue(struct rv_jit_context *ctx);
-- 
2.25.1