[PATCH v2 6/8] objtool/klp: Add LoongArch jump opcode bytes support

[George Guo <dongtai.guo@linux.dev>]

From: George Guo <guodongtai@kylinos.cn>

Implement arch_jump_opcode_bytes() for LoongArch so that klp checksums
for jump/call instructions with non-relocated destination offsets are
position-independent, mirroring the x86 and arm64 implementations.

Mask out the embedded branch offset while preserving the opcode and the
register operands, which differ per instruction format:

  - B/BL (reg0i26):                  no regs -> 0xfc000000
  - BEQZ/BNEZ/BCEQZ/BCNEZ (reg1i21): keep rj/cj -> 0xfc0003e0
  - JIRL/BEQ/BNE/.../BGEU (reg2i16): keep rj/rd -> 0xfc0003ff

Co-developed-by: Kexin Liu <liukexin@kylinos.cn>
Signed-off-by: Kexin Liu <liukexin@kylinos.cn>
Signed-off-by: George Guo <guodongtai@kylinos.cn>
---
 tools/objtool/arch/loongarch/decode.c | 41 +++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/tools/objtool/arch/loongarch/decode.c b/tools/objtool/arch/loongarch/decode.c
index 674e4efd138f..12facd0cc8d1 100644
--- a/tools/objtool/arch/loongarch/decode.c
+++ b/tools/objtool/arch/loongarch/decode.c
@@ -432,6 +432,47 @@ unsigned long arch_jump_table_sym_offset(struct reloc *reloc, struct reloc *tabl
 	}
 }
 
+size_t arch_jump_opcode_bytes(struct objtool_file *file, struct instruction *insn,
+			      unsigned char *buf)
+{
+	union loongarch_instruction *code;
+	u32 insn_word;
+
+	insn_word = le32toh(*(u32 *)(insn->sec->data->d_buf + insn->offset));
+	code = (union loongarch_instruction *)&insn_word;
+
+	switch (code->reg0i26_format.opcode) {
+	case b_op:
+	case bl_op:
+		/* reg0i26: 26-bit offset, no register operands */
+		insn_word &= 0xfc000000;
+		break;
+	case beqz_op:
+	case bnez_op:
+	case bceqz_op:		/* == bcnez_op */
+		/* reg1i21: keep opcode + rj/cj at bits[9:5] */
+		insn_word &= 0xfc0003e0;
+		break;
+	case jirl_op:
+	case beq_op:
+	case bne_op:
+	case blt_op:
+	case bge_op:
+	case bltu_op:
+	case bgeu_op:
+		/* reg2i16: keep opcode + rj/rd at bits[9:0] */
+		insn_word &= 0xfc0003ff;
+		break;
+	default:
+		break;
+	}
+
+	insn_word = htole32(insn_word);
+	memcpy(buf, &insn_word, sizeof(insn_word));
+
+	return LOONGARCH_INSN_SIZE;
+}
+
 #ifdef DISAS
 
 int arch_disas_info_init(struct disassemble_info *dinfo)
-- 
2.25.1