[RFC bpf-next 1/2] bpf, mips: Factor narrow loads out of emit_ldx()

[Nicholas Dudar]

Factor the byte, half-word, and word load selection out of emit_ldx()
in both MIPS JIT backends. The existing unsigned LDX paths remain the
only callers and retain the same native instructions, upper-half
handling, and clobber accounting. The double-word paths remain
unchanged.

This gives narrow loads one width dispatcher that can be extended
without duplicating the BPF size switch. No functional change
intended.

Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Nicholas Dudar <main.kalliope@xxxxxxxxx>
---
 arch/mips/net/bpf_jit_comp32.c | 28 ++++++++++++++++++++--------
 arch/mips/net/bpf_jit_comp64.c | 18 ++++++++++++++++--
 2 files changed, 36 insertions(+), 10 deletions(-)

diff --git a/arch/mips/net/bpf_jit_comp32.c b/arch/mips/net/bpf_jit_comp32.c
index b3f6b92ac34ed..48a3c834453f2 100644
--- a/arch/mips/net/bpf_jit_comp32.c
+++ b/arch/mips/net/bpf_jit_comp32.c
@@ -707,24 +707,36 @@ static void emit_trunc_r64(struct jit_context *ctx, const u8 dst[], u32 width)
 	}
 }
 
-/* Load operation: dst = *(size*)(src + off) */
-static void emit_ldx(struct jit_context *ctx,
-		     const u8 dst[], u8 src, s16 off, u8 size)
+/* Narrow load operation: dst = *(size *)(src + off) */
+static void emit_ldx_narrow(struct jit_context *ctx,
+			    u8 dst, u8 src, s16 off, u8 size)
 {
 	switch (size) {
 	/* Load a byte */
 	case BPF_B:
-		emit(ctx, lbu, lo(dst), off, src);
-		emit(ctx, move, hi(dst), MIPS_R_ZERO);
+		emit(ctx, lbu, dst, off, src);
 		break;
 	/* Load a half word */
 	case BPF_H:
-		emit(ctx, lhu, lo(dst), off, src);
-		emit(ctx, move, hi(dst), MIPS_R_ZERO);
+		emit(ctx, lhu, dst, off, src);
 		break;
 	/* Load a word */
 	case BPF_W:
-		emit(ctx, lw, lo(dst), off, src);
+		emit(ctx, lw, dst, off, src);
+		break;
+	}
+}
+
+/* Load operation: dst = *(size *)(src + off) */
+static void emit_ldx(struct jit_context *ctx,
+		     const u8 dst[], u8 src, s16 off, u8 size)
+{
+	switch (size) {
+	/* Load a byte, half word or word */
+	case BPF_B:
+	case BPF_H:
+	case BPF_W:
+		emit_ldx_narrow(ctx, lo(dst), src, off, size);
 		emit(ctx, move, hi(dst), MIPS_R_ZERO);
 		break;
 	/* Load a double word */
diff --git a/arch/mips/net/bpf_jit_comp64.c b/arch/mips/net/bpf_jit_comp64.c
index ee99f46828c86..22fb58f970223 100644
--- a/arch/mips/net/bpf_jit_comp64.c
+++ b/arch/mips/net/bpf_jit_comp64.c
@@ -398,8 +398,9 @@ static void emit_trunc_r64(struct jit_context *ctx, u8 dst, u32 width)
 	clobber_reg(ctx, dst);
 }
 
-/* Load operation: dst = *(size*)(src + off) */
-static void emit_ldx(struct jit_context *ctx, u8 dst, u8 src, s16 off, u8 size)
+/* Narrow load operation: dst = *(size *)(src + off) */
+static void emit_ldx_narrow(struct jit_context *ctx,
+			    u8 dst, u8 src, s16 off, u8 size)
 {
 	switch (size) {
 	/* Load a byte */
@@ -414,6 +415,19 @@ static void emit_ldx(struct jit_context *ctx, u8 dst, u8 src, s16 off, u8 size)
 	case BPF_W:
 		emit(ctx, lwu, dst, off, src);
 		break;
+	}
+}
+
+/* Load operation: dst = *(size *)(src + off) */
+static void emit_ldx(struct jit_context *ctx, u8 dst, u8 src, s16 off, u8 size)
+{
+	switch (size) {
+	/* Load a byte, half word or word */
+	case BPF_B:
+	case BPF_H:
+	case BPF_W:
+		emit_ldx_narrow(ctx, dst, src, off, size);
+		break;
 	/* Load a double word */
 	case BPF_DW:
 		emit(ctx, ld, dst, off, src);