rep movs* implementation

src/striga/semantics.py

@@ -63,6 +63,7 @@ class GPR(NamedTuple):
     "af": 4,
     "zf": 6,
     "sf": 7,
+    "df": 10,
     "of": 11,
 }
 
@@ -123,6 +124,7 @@ def __init__(self, module: Module, *, verbose=False):
             "of": 8,
             "pf": 8,
             "af": 8,
+            "df": 8,
         }
         self.reg_types = {
             name: types.int_n(size) for name, size in self.reg_sizes.items()

src/striga/x86/control.py

@@ -403,6 +403,16 @@ def clc(sem: Semantics):
     sem.flag_write("cf", sem.i1.constant(0))
 
 
+@semantic
+def std(sem: Semantics):
+    sem.flag_write("df", sem.i1.constant(1))
+
+
+@semantic
+def cld(sem: Semantics):
+    sem.flag_write("df", sem.i1.constant(0))
+
+
 @semantic
 def int_(sem: Semantics):
     sem.ir.ret_void()

src/striga/x86/data.py

@@ -1,6 +1,6 @@
-from capstone import CS_OP_REG
-from llvm import lookup_intrinsic_id
-from ..semantics import FLAGS, Semantics, semantic
+from capstone import CS_OP_REG, CS_OP_MEM
+from llvm import lookup_intrinsic_id, IntPredicate
+from ..semantics import FLAGS, Semantics, Successor, semantic, _semantics
 
 
 @semantic
@@ -168,3 +168,68 @@ def xchg(sem: Semantics):
     dst = sem.op_read(0)
     sem.op_write(0, src)
     sem.op_write(1, dst)
+
+
+def _movs_step(sem: Semantics):
+    size = sem.insn.operands[0].size
+    sem.op_write(0, sem.op_read(1))
+    df = sem.flag_read("df")
+    delta = sem.ir.select(
+        df, sem.const64(-size, sign_extend=True), sem.const64(size)
+    )
+    sem.reg_write("rsi", sem.ir.add(sem.reg_read("rsi"), delta))
+    sem.reg_write("rdi", sem.ir.add(sem.reg_read("rdi"), delta))
+
+
+@semantic
+def movsb(sem: Semantics):
+    _movs_step(sem)
+
+
+@semantic
+def movsw(sem: Semantics):
+    _movs_step(sem)
+
+
+@semantic
+def movsq(sem: Semantics):
+    _movs_step(sem)
+
+
+@semantic
+def movsd(sem: Semantics):
+    if all(op.type == CS_OP_MEM for op in sem.insn.operands):
+        _movs_step(sem)
+    else:
+        mov(sem)
+
+
+def _rep(sem: Semantics, step_fn):
+    addr = sem.insn.address
+    fallthrough = addr + sem.insn.size
+    check = sem.function.append_basic_block(f"rep_check_{addr:#x}")
+    body = sem.function.append_basic_block(f"rep_body_{addr:#x}")
+    exit_block = sem.get_or_create_block(fallthrough)
+
+    sem.ir.br(check)
+
+    with check.create_builder() as ir:
+        sem.ir = ir
+        cond = sem.ir.icmp(IntPredicate.NE, sem.reg_read("rcx"), sem.const64(0))
+        sem.ir.cond_br(cond, body, exit_block)
+
+    with body.create_builder() as ir:
+        sem.ir = ir
+        step_fn(sem)
+        sem.reg_write("rcx", sem.ir.sub(sem.reg_read("rcx"), sem.const64(1)))
+        sem.ir.br(check)
+
+    return [Successor(addr, sem.const64(fallthrough))]
+
+
+def _rep_movs(sem: Semantics):
+    return _rep(sem, _movs_step)
+
+
+for _m in ("rep movsb", "rep movsw", "rep movsd", "rep movsq"):
+    _semantics[_m] = _rep_movs