asm: add initial support for memory operand only instructions

* add dec, inc instruction for with memory operand

4 files changed, 174 insertions, 4 deletions

diff --git a/src/asm.rs b/src/asm.rs
index 7deeb70..711de8a 100644
--- a/src/asm.rs
+++ b/src/asm.rs
@@ -154,6 +154,52 @@ impl Asm {
         self.emit(&[opc, modrm]);
     }
 
+    /// Encode a memory operand instruction.
+    pub(crate) fn encode_m<T: MemOpSized>(&mut self, opc: u8, opc_ext: u8, op1: T)
+    where
+        Self: EncodeM<T>,
+    {
+        let op1 = op1.mem_op();
+
+        // M operand encoding.
+        //   op1 -> modrm.rm
+        let (mode, rm) = match op1 {
+            MemOp::Indirect(..) => {
+                assert!(!op1.base().need_sib() && !op1.base().is_pc_rel());
+                (0b00, op1.base().idx())
+            }
+            MemOp::IndirectDisp(..) => {
+                assert!(!op1.base().need_sib());
+                (0b10, op1.base().idx())
+            }
+            MemOp::IndirectBaseIndex(..) => {
+                assert!(!op1.base().is_pc_rel());
+                // Using rsp as index register is interpreted as just base w/o offset.
+                //   https://wiki.osdev.org/X86-64_Instruction_Encoding#32.2F64-bit_addressing_2
+                // Disallow this case, as guard for the user.
+                assert!(!matches!(op1.index(), Reg64::rsp));
+                (0b00, 0b100)
+            }
+        };
+
+        let modrm = modrm(
+            mode,    /* mode */
+            opc_ext, /* reg */
+            rm,      /* rm */
+        );
+
+        let prefix = <Self as EncodeM<T>>::legacy_prefix();
+        let rex = <Self as EncodeM<T>>::rex(&op1);
+
+        self.emit_optional(&[prefix, rex]);
+        self.emit(&[opc, modrm]);
+        match op1 {
+            MemOp::Indirect(..) => {}
+            MemOp::IndirectDisp(_, disp) => self.emit(&disp.to_ne_bytes()),
+            MemOp::IndirectBaseIndex(base, index) => self.emit(&[sib(0, index.idx(), base.idx())]),
+        }
+    }
+
     /// Encode a memory-immediate instruction.
     pub(crate) fn encode_mi<T: Imm>(&mut self, opc: u8, opc_ext: u8, op1: MemOp, op2: T)
     where
@@ -330,7 +376,7 @@ pub(crate) trait EncodeMR<T: Reg> {
     }
 
     fn rex(op1: &MemOp, op2: T) -> Option<u8> {
-        if op2.need_rex() || (op1.base().is_ext()) {
+        if op2.need_rex() || op1.base().is_ext() || op1.index().is_ext() {
             Some(rex(
                 op2.rexw(),
                 op2.idx(),
@@ -359,7 +405,7 @@ pub(crate) trait EncodeMI<T: Imm> {
     }
 
     fn rex(op1: &MemOp) -> Option<u8> {
-        if op1.base().is_ext() {
+        if op1.base().is_ext() || op1.index().is_ext() {
             Some(rex(false, 0, op1.index().idx(), op1.base().idx()))
         } else {
             None
@@ -374,3 +420,40 @@ impl EncodeMI<Imm16> for Asm {
     }
 }
 impl EncodeMI<Imm32> for Asm {}
+
+/// Encode helper for memory operand instructions.
+pub(crate) trait EncodeM<T: MemOpSized> {
+    fn legacy_prefix() -> Option<u8> {
+        None
+    }
+
+    fn rex(op1: &MemOp) -> Option<u8> {
+        if op1.base().is_ext() || op1.index().is_ext() || Self::is_64bit() {
+            Some(rex(
+                Self::is_64bit(),
+                0,
+                op1.index().idx(),
+                op1.base().idx(),
+            ))
+        } else {
+            None
+        }
+    }
+
+    fn is_64bit() -> bool {
+        false
+    }
+}
+
+impl EncodeM<MemOp8> for Asm {}
+impl EncodeM<MemOp16> for Asm {
+    fn legacy_prefix() -> Option<u8> {
+        Some(0x66)
+    }
+}
+impl EncodeM<MemOp32> for Asm {}
+impl EncodeM<MemOp64> for Asm {
+    fn is_64bit() -> bool {
+        true
+    }
+}
diff --git a/src/insn/dec.rs b/src/insn/dec.rs
index 1377d1c..66b83aa 100644
--- a/src/insn/dec.rs
+++ b/src/insn/dec.rs
@@ -1,5 +1,5 @@
 use super::Dec;
-use crate::{Asm, Reg32, Reg64};
+use crate::{Asm, MemOp16, MemOp32, MemOp64, MemOp8, Reg32, Reg64};
 
 impl Dec<Reg64> for Asm {
     fn dec(&mut self, op1: Reg64) {
@@ -12,3 +12,27 @@ impl Dec<Reg32> for Asm {
         self.encode_r(0xff, 1, op1);
     }
 }
+
+impl Dec<MemOp8> for Asm {
+    fn dec(&mut self, op1: MemOp8) {
+        self.encode_m(0xfe, 1, op1);
+    }
+}
+
+impl Dec<MemOp16> for Asm {
+    fn dec(&mut self, op1: MemOp16) {
+        self.encode_m(0xff, 1, op1);
+    }
+}
+
+impl Dec<MemOp32> for Asm {
+    fn dec(&mut self, op1: MemOp32) {
+        self.encode_m(0xff, 1, op1);
+    }
+}
+
+impl Dec<MemOp64> for Asm {
+    fn dec(&mut self, op1: MemOp64) {
+        self.encode_m(0xff, 1, op1);
+    }
+}
diff --git a/src/insn/inc.rs b/src/insn/inc.rs
index ede780a..1530d63 100644
--- a/src/insn/inc.rs
+++ b/src/insn/inc.rs
@@ -1,5 +1,5 @@
 use super::Inc;
-use crate::{Asm, Reg32, Reg64};
+use crate::{Asm, MemOp16, MemOp32, MemOp64, MemOp8, Reg32, Reg64};
 
 impl Inc<Reg64> for Asm {
     fn inc(&mut self, op1: Reg64) {
@@ -12,3 +12,27 @@ impl Inc<Reg32> for Asm {
         self.encode_r(0xff, 0, op1);
     }
 }
+
+impl Inc<MemOp8> for Asm {
+    fn inc(&mut self, op1: MemOp8) {
+        self.encode_m(0xfe, 0, op1);
+    }
+}
+
+impl Inc<MemOp16> for Asm {
+    fn inc(&mut self, op1: MemOp16) {
+        self.encode_m(0xff, 0, op1);
+    }
+}
+
+impl Inc<MemOp32> for Asm {
+    fn inc(&mut self, op1: MemOp32) {
+        self.encode_m(0xff, 0, op1);
+    }
+}
+
+impl Inc<MemOp64> for Asm {
+    fn inc(&mut self, op1: MemOp64) {
+        self.encode_m(0xff, 0, op1);
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 131440a..6bbfcbf 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -88,6 +88,7 @@ pub use reg::{Reg16, Reg32, Reg64, Reg8};
 pub use rt::Runtime;
 
 /// Type representing a memory operand.
+#[derive(Clone, Copy)]
 pub enum MemOp {
     /// An indirect memory operand, eg `mov [rax], rcx`.
     Indirect(Reg64),
@@ -123,3 +124,41 @@ impl MemOp {
         }
     }
 }
+
+/// Trait to give size hints for memory operands.
+trait MemOpSized {
+    fn mem_op(&self) -> MemOp;
+}
+
+macro_rules! impl_memop_sized {
+    ($(#[$doc:meta] $name:ident)+) => {
+        $(
+        #[$doc]
+        pub struct $name(MemOp);
+
+        impl $name {
+            /// Create a memory with size hint from a raw memory operand.
+            pub fn from(op: MemOp) -> Self {
+                Self(op)
+            }
+        }
+
+        impl MemOpSized for $name {
+            fn mem_op(&self) -> MemOp {
+                self.0
+            }
+        }
+        )+
+    };
+}
+
+impl_memop_sized!(
+    /// A memory operand with a word (8 bit) size hint.
+    MemOp8
+    /// A memory operand with a word (16 bit) size hint.
+    MemOp16
+    /// A memory operand with a dword (32 bit) size hint.
+    MemOp32
+    /// A memory operand with a qword (64 bit) size hint.
+    MemOp64
+);