riscv64,exec: add more amo instructions

src/isa/riscv64/exec/all-instr.h

@@ -58,3 +58,5 @@ make_EHelper(amoswap);
 make_EHelper(amoadd);
 make_EHelper(amoor);
 make_EHelper(amoand);
+make_EHelper(amomaxu);
+make_EHelper(amoxor);

src/isa/riscv64/exec/amo.c

@@ -61,3 +61,17 @@ make_EHelper(amoand) {
   amo_update();
   print_asm_template3(amoand);
 }
+
+make_EHelper(amomaxu) {
+  amo_load();
+  s1 = (s0 > id_src2->val ? s0 : id_src2->val);
+  amo_update();
+  print_asm_template3(amomaxu);
+}
+
+make_EHelper(amoxor) {
+  amo_load();
+  rtl_xor(&s1, &s0, &id_src2->val);
+  amo_update();
+  print_asm_template3(amoxor);
+}

src/isa/riscv64/exec/exec.c

@@ -72,7 +72,7 @@ static make_EHelper(atomic) {
     EMPTY, EX(amoswap), EX(lr), EX(sc)
   };
   static OpcodeEntry table_hi [8] = {
-    EX(amoadd), EMPTY, EX(amoor), EX(amoand), EMPTY, EMPTY, EMPTY, EMPTY
+    EX(amoadd), EX(amoxor), EX(amoor), EX(amoand), EMPTY, EMPTY, EMPTY, EX(amomaxu)
   };
 
   decinfo.width = 1 << decinfo.isa.instr.funct3;