arm32, bpf: add support for 32-bit signed division

The cpuv4 added a new BPF_SDIV instruction that does signed division.
The encoding is similar to BPF_DIV but BPF_SDIV sets offset=1.

ARM32 already supports 32-bit BPF_DIV which can be easily extended to
support BPF_SDIV as ARM32 has the SDIV instruction. When the CPU is not
ARM-v7, we implement that SDIV/SMOD with the function call similar to
the implementation of DIV/MOD.

Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/20230907230550.1417590-6-puranjay12@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: puranjaymohan

arch/arm/net/bpf_jit_32.c

@@ -228,6 +228,16 @@ static u32 jit_mod32(u32 dividend, u32 divisor)
 	return dividend % divisor;
 }
 
+static s32 jit_sdiv32(s32 dividend, s32 divisor)
+{
+	return dividend / divisor;
+}
+
+static s32 jit_smod32(s32 dividend, s32 divisor)
+{
+	return dividend % divisor;
+}
+
 static inline void _emit(int cond, u32 inst, struct jit_ctx *ctx)
 {
 	inst |= (cond << 28);
@@ -477,17 +487,18 @@ static inline int epilogue_offset(const struct jit_ctx *ctx)
 	return to - from - 2;
 }
 
-static inline void emit_udivmod(u8 rd, u8 rm, u8 rn, struct jit_ctx *ctx, u8 op)
+static inline void emit_udivmod(u8 rd, u8 rm, u8 rn, struct jit_ctx *ctx, u8 op, u8 sign)
 {
 	const int exclude_mask = BIT(ARM_R0) | BIT(ARM_R1);
 	const s8 *tmp = bpf2a32[TMP_REG_1];
+	u32 dst;
 
 #if __LINUX_ARM_ARCH__ == 7
 	if (elf_hwcap & HWCAP_IDIVA) {
-		if (op == BPF_DIV)
-			emit(ARM_UDIV(rd, rm, rn), ctx);
-		else {
-			emit(ARM_UDIV(ARM_IP, rm, rn), ctx);
+		if (op == BPF_DIV) {
+			emit(sign ? ARM_SDIV(rd, rm, rn) : ARM_UDIV(rd, rm, rn), ctx);
+		} else {
+			emit(sign ? ARM_SDIV(ARM_IP, rm, rn) : ARM_UDIV(ARM_IP, rm, rn), ctx);
 			emit(ARM_MLS(rd, rn, ARM_IP, rm), ctx);
 		}
 		return;
@@ -515,8 +526,19 @@ static inline void emit_udivmod(u8 rd, u8 rm, u8 rn, struct jit_ctx *ctx, u8 op)
 	emit(ARM_PUSH(CALLER_MASK & ~exclude_mask), ctx);
 
 	/* Call appropriate function */
-	emit_mov_i(ARM_IP, op == BPF_DIV ?
-		   (u32)jit_udiv32 : (u32)jit_mod32, ctx);
+	if (sign) {
+		if (op == BPF_DIV)
+			dst = (u32)jit_sdiv32;
+		else
+			dst = (u32)jit_smod32;
+	} else {
+		if (op == BPF_DIV)
+			dst = (u32)jit_udiv32;
+		else
+			dst = (u32)jit_mod32;
+	}
+
+	emit_mov_i(ARM_IP, dst, ctx);
 	emit_blx_r(ARM_IP, ctx);
 
 	/* Restore caller-saved registers from stack */
@@ -1551,7 +1573,7 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
 			rt = src_lo;
 			break;
 		}
-		emit_udivmod(rd_lo, rd_lo, rt, ctx, BPF_OP(code));
+		emit_udivmod(rd_lo, rd_lo, rt, ctx, BPF_OP(code), off);
 		arm_bpf_put_reg32(dst_lo, rd_lo, ctx);
 		if (!ctx->prog->aux->verifier_zext)
 			emit_a32_mov_i(dst_hi, 0, ctx);

arch/arm/net/bpf_jit_32.h

@@ -139,6 +139,7 @@
 #define ARM_INST_TST_I		0x03100000
 
 #define ARM_INST_UDIV		0x0730f010
+#define ARM_INST_SDIV		0x0710f010
 
 #define ARM_INST_UMULL		0x00800090
 
@@ -267,6 +268,7 @@
 #define ARM_TST_I(rn, imm)	_AL3_I(ARM_INST_TST, 0, rn, imm)
 
 #define ARM_UDIV(rd, rn, rm)	(ARM_INST_UDIV | (rd) << 16 | (rn) | (rm) << 8)
+#define ARM_SDIV(rd, rn, rm)	(ARM_INST_SDIV | (rd) << 16 | (rn) | (rm) << 8)
 
 #define ARM_UMULL(rd_lo, rd_hi, rn, rm)	(ARM_INST_UMULL | (rd_hi) << 16 \
 					 | (rd_lo) << 12 | (rm) << 8 | rn)