disas/riscv: Provide infrastructure for vendor extensions

A previous patch provides a pointer to the RISCVCPUConfig data.
Let's use this to add the necessary code for vendor extensions.
This patch does not change the current behaviour, but clearly
defines how vendor extension support can be added to the disassembler.

Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
Message-Id: <20230612111034.3955227-7-christoph.muellner@vrull.eu>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

disas/riscv.c

@@ -4700,9 +4700,33 @@ disasm_inst(char *buf, size_t buflen, rv_isa isa, uint64_t pc, rv_inst inst,
     rv_decode dec = { 0 };
     dec.pc = pc;
     dec.inst = inst;
-    dec.opcode_data = rvi_opcode_data;
     dec.cfg = cfg;
-    decode_inst_opcode(&dec, isa);
+
+    static const struct {
+        bool (*guard_func)(const RISCVCPUConfig *);
+        const rv_opcode_data *opcode_data;
+        void (*decode_func)(rv_decode *, rv_isa);
+    } decoders[] = {
+        { always_true_p, rvi_opcode_data, decode_inst_opcode },
+    };
+
+    for (size_t i = 0; i < ARRAY_SIZE(decoders); i++) {
+        bool (*guard_func)(const RISCVCPUConfig *) = decoders[i].guard_func;
+        const rv_opcode_data *opcode_data = decoders[i].opcode_data;
+        void (*decode_func)(rv_decode *, rv_isa) = decoders[i].decode_func;
+
+        if (guard_func(cfg)) {
+            dec.opcode_data = opcode_data;
+            decode_func(&dec, isa);
+            if (dec.op != rv_op_illegal)
+                break;
+        }
+    }
+
+    if (dec.op == rv_op_illegal) {
+        dec.opcode_data = rvi_opcode_data;
+    }
+
     decode_inst_operands(&dec, isa);
     decode_inst_decompress(&dec, isa);
     decode_inst_lift_pseudo(&dec);