[PATCH bpf-next 2/7] arm64: insn: Add encoder for ADD/SUB (extended register)

[Puranjay Mohan <puranjay@kernel.org>]

From: Tejun Heo <tj@kernel.org>

The insn library encodes the immediate and shifted-register forms of
ADD/SUB but not the extended-register form. The BPF JIT wants it to
rebase a 32-bit arena offset onto the arena kernel base in a single
instruction, add xN, xBASE, wN, uxtw, instead of a separate zero-extend
followed by a plain add.

Add aarch64_insn_gen_add_sub_extended_reg(), modeled on the
shifted-register generator. The option and imm3 fields occupy the same
bits as the shifted form's shift amount, so they are encoded through the
existing IMM_6 field type.

Note that register 31 does not mean the same thing in the two forms: in
the extended-register encoding it is SP for Rn, and for Rd unless the
instruction sets the flags, while it stays XZR for Rm. Callers porting a
shifted-register site that passes A64_ZR need to be aware of that, so
say so above the function.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
---
 arch/arm64/include/asm/insn.h | 23 ++++++++++++++
 arch/arm64/lib/insn.c         | 60 +++++++++++++++++++++++++++++++++++
 2 files changed, 83 insertions(+)

diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
index cc0702fa64a79..4548e8015808d 100644
--- a/arch/arm64/include/asm/insn.h
+++ b/arch/arm64/include/asm/insn.h
@@ -205,6 +205,18 @@ enum aarch64_insn_adsb_type {
 	AARCH64_INSN_ADSB_SUB_SETFLAGS
 };
 
+/* option field of add/sub (extended register) */
+enum aarch64_insn_extend_type {
+	AARCH64_INSN_EXTEND_UXTB,
+	AARCH64_INSN_EXTEND_UXTH,
+	AARCH64_INSN_EXTEND_UXTW,
+	AARCH64_INSN_EXTEND_UXTX,
+	AARCH64_INSN_EXTEND_SXTB,
+	AARCH64_INSN_EXTEND_SXTH,
+	AARCH64_INSN_EXTEND_SXTW,
+	AARCH64_INSN_EXTEND_SXTX,
+};
+
 enum aarch64_insn_movewide_type {
 	AARCH64_INSN_MOVEWIDE_ZERO,
 	AARCH64_INSN_MOVEWIDE_KEEP,
@@ -378,6 +390,10 @@ __AARCH64_INSN_FUNCS(add,	0x7F200000, 0x0B000000)
 __AARCH64_INSN_FUNCS(adds,	0x7F200000, 0x2B000000)
 __AARCH64_INSN_FUNCS(sub,	0x7F200000, 0x4B000000)
 __AARCH64_INSN_FUNCS(subs,	0x7F200000, 0x6B000000)
+__AARCH64_INSN_FUNCS(add_ext,	0x7F200000, 0x0B200000)
+__AARCH64_INSN_FUNCS(adds_ext,	0x7F200000, 0x2B200000)
+__AARCH64_INSN_FUNCS(sub_ext,	0x7F200000, 0x4B200000)
+__AARCH64_INSN_FUNCS(subs_ext,	0x7F200000, 0x6B200000)
 __AARCH64_INSN_FUNCS(madd,	0x7FE08000, 0x1B000000)
 __AARCH64_INSN_FUNCS(msub,	0x7FE08000, 0x1B008000)
 __AARCH64_INSN_FUNCS(udiv,	0x7FE0FC00, 0x1AC00800)
@@ -637,6 +653,13 @@ u32 aarch64_insn_gen_add_sub_shifted_reg(enum aarch64_insn_register dst,
 					 int shift,
 					 enum aarch64_insn_variant variant,
 					 enum aarch64_insn_adsb_type type);
+u32 aarch64_insn_gen_add_sub_extended_reg(enum aarch64_insn_register dst,
+					  enum aarch64_insn_register src,
+					  enum aarch64_insn_register reg,
+					  enum aarch64_insn_extend_type extend,
+					  int shift,
+					  enum aarch64_insn_variant variant,
+					  enum aarch64_insn_adsb_type type);
 u32 aarch64_insn_gen_data1(enum aarch64_insn_register dst,
 			   enum aarch64_insn_register src,
 			   enum aarch64_insn_variant variant,
diff --git a/arch/arm64/lib/insn.c b/arch/arm64/lib/insn.c
index 37ce75f7f1f08..e70ac02385153 100644
--- a/arch/arm64/lib/insn.c
+++ b/arch/arm64/lib/insn.c
@@ -986,6 +986,66 @@ u32 aarch64_insn_gen_add_sub_shifted_reg(enum aarch64_insn_register dst,
 	return aarch64_insn_encode_immediate(AARCH64_INSN_IMM_6, insn, shift);
 }
 
+/*
+ * Unlike the shifted-register form, register 31 is not XZR everywhere here:
+ * it encodes SP for @src, and for @dst too unless @type sets the flags. Only
+ * @reg keeps the XZR meaning.
+ */
+u32 aarch64_insn_gen_add_sub_extended_reg(enum aarch64_insn_register dst,
+					  enum aarch64_insn_register src,
+					  enum aarch64_insn_register reg,
+					  enum aarch64_insn_extend_type extend,
+					  int shift,
+					  enum aarch64_insn_variant variant,
+					  enum aarch64_insn_adsb_type type)
+{
+	u32 insn;
+
+	switch (type) {
+	case AARCH64_INSN_ADSB_ADD:
+		insn = aarch64_insn_get_add_ext_value();
+		break;
+	case AARCH64_INSN_ADSB_SUB:
+		insn = aarch64_insn_get_sub_ext_value();
+		break;
+	case AARCH64_INSN_ADSB_ADD_SETFLAGS:
+		insn = aarch64_insn_get_adds_ext_value();
+		break;
+	case AARCH64_INSN_ADSB_SUB_SETFLAGS:
+		insn = aarch64_insn_get_subs_ext_value();
+		break;
+	default:
+		pr_err("%s: unknown add/sub encoding %d\n", __func__, type);
+		return AARCH64_BREAK_FAULT;
+	}
+
+	switch (variant) {
+	case AARCH64_INSN_VARIANT_32BIT:
+		break;
+	case AARCH64_INSN_VARIANT_64BIT:
+		insn |= AARCH64_INSN_SF_BIT;
+		break;
+	default:
+		pr_err("%s: unknown variant encoding %d\n", __func__, variant);
+		return AARCH64_BREAK_FAULT;
+	}
+
+	if (shift < 0 || shift > 4) {
+		pr_err("%s: invalid shift encoding %d\n", __func__, shift);
+		return AARCH64_BREAK_FAULT;
+	}
+
+	insn = aarch64_insn_encode_register(AARCH64_INSN_REGTYPE_RD, insn, dst);
+
+	insn = aarch64_insn_encode_register(AARCH64_INSN_REGTYPE_RN, insn, src);
+
+	insn = aarch64_insn_encode_register(AARCH64_INSN_REGTYPE_RM, insn, reg);
+
+	/* option in bits [15:13] and imm3 in [12:10] together fill IMM_6 */
+	return aarch64_insn_encode_immediate(AARCH64_INSN_IMM_6, insn,
+					     (extend << 3) | shift);
+}
+
 u32 aarch64_insn_gen_data1(enum aarch64_insn_register dst,
 			   enum aarch64_insn_register src,
 			   enum aarch64_insn_variant variant,
-- 
2.53.0-Meta