x86_64-asm: support endbr64 instruction

endbr64 has no operand but comes with a ModR/M byte. Handle it in the same way as *fence instructions. Co-authored-by: Yao Zi <[email protected]> Signed-off-by: Yao Zi <[email protected]> Signed-off-by: John Nunley <[email protected]>
TinyCC · Oct 27, 2024 · a21b5f1 · a21b5f1
1 parent 6acf301
commit a21b5f1
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Showing 2 changed files with 12 additions and 3 deletions.
diff --git a/i386-asm.c b/i386-asm.c
@@ -1002,15 +1002,21 @@ ST_FUNC void asm_opcode(TCCState *s1, int opcode)
     modrm_index = -1;
     modreg_index = -1;
     if (pa->instr_type & OPC_MODRM) {
+#ifdef TCC_TARGET_X86_64
 	if (!nb_ops) {
 	    /* A modrm opcode without operands is a special case (e.g. mfence).
-	       It has a group and acts as if there's an register operand 0
-	       (ax).  */
+	       It has a group and acts as if there's an register operand 0 */
 	    i = 0;
 	    ops[i].type = OP_REG;
-	    ops[i].reg = 0;
+	    if (pa->sym == TOK_ASM_endbr64)
+	      ops[i].reg = 2; // dx
+	    else if (pa->sym >= TOK_ASM_lfence && pa->sym <= TOK_ASM_sfence)
+  	      ops[i].reg = 0; // ax
+	    else
+	      tcc_error("bad MODR/M opcode without operands");
 	    goto modrm_found;
 	}
+#endif
         /* first look for an ea operand */
         for(i = 0;i < nb_ops; i++) {
             if (op_type[i] & OP_EA)

diff --git a/x86_64-asm.h b/x86_64-asm.h
@@ -538,6 +538,9 @@ ALT(DEF_ASM_OP2(movhps, 0x0f17, 0, OPC_MODRM, OPT_SSE, OPT_EA | OPT_REG32 ))
     DEF_ASM_OP0L(mfence, 0x0fae, 6, OPC_MODRM)
     DEF_ASM_OP0L(sfence, 0x0fae, 7, OPC_MODRM)
     DEF_ASM_OP1(clflush, 0x0fae, 7, OPC_MODRM, OPT_EA)
+
+    /* Control-Flow Enforcement */
+    DEF_ASM_OP0L(endbr64, 0xf30f1e, 7, OPC_MODRM)
 #undef ALT
 #undef DEF_ASM_OP0
 #undef DEF_ASM_OP0L