s390/dis: Instruction decoding interface

Provide a new function, insn_to_mnemonic, by which e.g. kvm can obtain
a human-readable decoding of an instruction's opcode.

Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/s390/include/asm/processor.h

@@ -138,6 +138,7 @@ extern int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags);
 extern unsigned long thread_saved_pc(struct task_struct *t);
 
 extern void show_code(struct pt_regs *regs);
+extern int insn_to_mnemonic(unsigned char *instruction, char buf[8]);
 
 unsigned long get_wchan(struct task_struct *p);
 #define task_pt_regs(tsk) ((struct pt_regs *) \

arch/s390/kernel/dis.c

@@ -1468,6 +1468,33 @@ static struct insn *find_insn(unsigned char *code)
 	return NULL;
 }
 
+/**
+ * insn_to_mnemonic - decode an s390 instruction
+ * @instruction: instruction to decode
+ * @buf: buffer to fill with mnemonic
+ *
+ * Decode the instruction at @instruction and store the corresponding
+ * mnemonic into @buf.
+ * @buf is left unchanged if the instruction could not be decoded.
+ * Returns:
+ *  %0 on success, %-ENOENT if the instruction was not found.
+ */
+int insn_to_mnemonic(unsigned char *instruction, char buf[8])
+{
+	struct insn *insn;
+
+	insn = find_insn(instruction);
+	if (!insn)
+		return -ENOENT;
+	if (insn->name[0] == '\0')
+		snprintf(buf, sizeof(buf), "%s",
+			 long_insn_name[(int) insn->name[1]]);
+	else
+		snprintf(buf, sizeof(buf), "%.5s", insn->name);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(insn_to_mnemonic);
+
 static int print_insn(char *buffer, unsigned char *code, unsigned long addr)
 {
 	struct insn *insn;