[PATCH bpf-next 2/2] bpf, parisc: Add support for BPF_SDIV and BPF_SMOD in the parisc32 JIT

[Nicholas Dudar]

emit_alu_r32() and emit_alu_r64() call the unsigned millicode
($$divU/$$remU) and libgcc-style (hppa_div64()/hppa_div64_rem())
divide/remainder helpers for BPF_DIV and BPF_MOD regardless of the
BPF instruction's signedness, so the parisc32 JIT does not implement
signed BPF_SDIV and BPF_SMOD (off == 1). Signed ALU32 and ALU64
div/mod get an unsigned quotient and remainder rather than the
verifier's and the interpreter's signed result for negative operands.

Thread is_signed = (insn->off == 1) through emit_alu_r32()/
emit_alu_r64(), and on the signed path use the $$divI/$$remI signed
millicode routines (32-bit) or the hppa_sdiv64()/hppa_sdiv64_rem()
helpers added in patch 1 (64-bit) instead of their unsigned
counterparts. $$divI and $$remI are extern-declared and exported next
to $$divU/$$remU in arch/parisc/kernel/parisc_ksyms.c.
bpf_do_misc_fixups() rewrites the zero-divisor and INT_MIN/-1 cases out
of the instruction stream before the JIT runs.

Signed-off-by: Nicholas Dudar <main.kalliope@xxxxxxxxx>
Assisted-by: Claude:claude-opus-4-8
---
 arch/parisc/net/bpf_jit_comp32.c | 29 +++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/arch/parisc/net/bpf_jit_comp32.c b/arch/parisc/net/bpf_jit_comp32.c
index 5ff0cf925fe9..eea0a34a3bfe 100644
--- a/arch/parisc/net/bpf_jit_comp32.c
+++ b/arch/parisc/net/bpf_jit_comp32.c
@@ -321,6 +321,8 @@ static void bpf_put_reg32(const s8 *reg, const s8 *src,
 extern void $$mulI(void);
 extern void $$divU(void);
 extern void $$remU(void);
+extern void $$divI(void);
+extern void $$remI(void);
 
 static void emit_call_millicode(void *func, const s8 arg0,
 		const s8 arg1, u8 opcode, struct hppa_jit_context *ctx)
@@ -562,12 +564,14 @@ static void emit_alu_i32(const s8 *dst, s32 imm,
 }
 
 static void emit_alu_r64(const s8 *dst, const s8 *src,
-			 struct hppa_jit_context *ctx, const u8 op)
+			 struct hppa_jit_context *ctx, const u8 op,
+			 bool is_signed)
 {
 	const s8 *tmp1 = regmap[TMP_REG_1];
 	const s8 *tmp2 = regmap[TMP_REG_2];
 	const s8 *rd;
 	const s8 *rs = bpf_get_reg64(src, tmp2, ctx);
+	void *func;
 
 	if (op == BPF_MOV)
 		rd = bpf_get_reg64_ref(dst, tmp1, false, ctx);
@@ -604,10 +608,12 @@ static void emit_alu_r64(const s8 *dst, const s8 *src,
 		emit_call_libgcc_ll(__muldi3, rd, rs, op, ctx);
 		break;
 	case BPF_DIV:
-		emit_call_libgcc_ll(&hppa_div64, rd, rs, op, ctx);
+		func = is_signed ? &hppa_sdiv64 : &hppa_div64;
+		emit_call_libgcc_ll(func, rd, rs, op, ctx);
 		break;
 	case BPF_MOD:
-		emit_call_libgcc_ll(&hppa_div64_rem, rd, rs, op, ctx);
+		func = is_signed ? &hppa_sdiv64_rem : &hppa_div64_rem;
+		emit_call_libgcc_ll(func, rd, rs, op, ctx);
 		break;
 	case BPF_LSH:
 		emit_call_libgcc_ll(__ashldi3, rd, rs, op, ctx);
@@ -630,7 +636,8 @@ static void emit_alu_r64(const s8 *dst, const s8 *src,
 }
 
 static void emit_alu_r32(const s8 *dst, const s8 *src,
-			 struct hppa_jit_context *ctx, const u8 op)
+			 struct hppa_jit_context *ctx, const u8 op,
+			 bool is_signed)
 {
 	const s8 *tmp1 = regmap[TMP_REG_1];
 	const s8 *tmp2 = regmap[TMP_REG_2];
@@ -666,10 +673,12 @@ static void emit_alu_r32(const s8 *dst, const s8 *src,
 		emit_call_millicode($$mulI, lo(rd), lo(rs), op, ctx);
 		break;
 	case BPF_DIV:
-		emit_call_millicode($$divU, lo(rd), lo(rs), op, ctx);
+		emit_call_millicode(is_signed ? $$divI : $$divU,
+				    lo(rd), lo(rs), op, ctx);
 		break;
 	case BPF_MOD:
-		emit_call_millicode($$remU, lo(rd), lo(rs), op, ctx);
+		emit_call_millicode(is_signed ? $$remI : $$remU,
+				    lo(rd), lo(rs), op, ctx);
 		break;
 	case BPF_LSH:
 		emit(hppa_subi(0x1f, lo(rs), HPPA_REG_T0), ctx);
@@ -1163,12 +1172,12 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct hppa_jit_context *ctx,
 			emit_imm32(tmp2, imm, ctx);
 			src = tmp2;
 		}
-		emit_alu_r64(dst, src, ctx, BPF_OP(code));
+		emit_alu_r64(dst, src, ctx, BPF_OP(code), off == 1);
 		break;
 
 	/* dst = -dst */
 	case BPF_ALU64 | BPF_NEG:
-		emit_alu_r64(dst, tmp2, ctx, BPF_OP(code));
+		emit_alu_r64(dst, tmp2, ctx, BPF_OP(code), false);
 		break;
 
 	case BPF_ALU64 | BPF_MOV | BPF_K:
@@ -1211,7 +1220,7 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct hppa_jit_context *ctx,
 			emit_imm32(tmp2, imm, ctx);
 			src = tmp2;
 		}
-		emit_alu_r32(dst, src, ctx, BPF_OP(code));
+		emit_alu_r32(dst, src, ctx, BPF_OP(code), off == 1);
 		break;
 
 	/* dst = dst OP imm */
@@ -1236,7 +1245,7 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct hppa_jit_context *ctx,
 		 * src is ignored---choose tmp2 as a dummy register since it
 		 * is not on the stack.
 		 */
-		emit_alu_r32(dst, tmp2, ctx, BPF_OP(code));
+		emit_alu_r32(dst, tmp2, ctx, BPF_OP(code), false);
 		break;
 
 	/* dst = BSWAP##imm(dst) */
-- 
2.34.1