From ec4e19d01ff401aad04dc1fcdb08781db83c4786 Mon Sep 17 00:00:00 2001
From: Brendan Hansknecht <brendan.hansknecht@gmail.com>
Date: Sun, 15 Nov 2020 21:05:53 -0800
Subject: [PATCH] Extract remain assembly to asm.rs

---
 compiler/gen_dev/src/x86_64/asm.rs | 27 ++++++++++++++++++++++++++-
 compiler/gen_dev/src/x86_64/mod.rs | 12 ++++--------
 2 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/compiler/gen_dev/src/x86_64/asm.rs b/compiler/gen_dev/src/x86_64/asm.rs
index 8ec5689947..8962c4e4af 100644
--- a/compiler/gen_dev/src/x86_64/asm.rs
+++ b/compiler/gen_dev/src/x86_64/asm.rs
@@ -22,7 +22,8 @@ pub enum Register {
     R15,
 }
 
-const REX_W: u8 = 0x48;
+const REX: u8 = 0x40;
+const REX_W: u8 = REX + 0x8;
 
 fn add_rm_extension(reg: Register, byte: u8) -> u8 {
     if reg as u8 > 7 {
@@ -68,3 +69,27 @@ pub fn mov_register64bit_register64bit<'a>(buf: &mut Vec<'a, u8>, dst: Register,
     let src_mod = (src as u8 % 8) << 3;
     buf.extend(&[rex, 0x89, 0xC0 + dst_mod + src_mod]);
 }
+
+pub fn ret_near<'a>(buf: &mut Vec<'a, u8>) {
+    buf.push(0xC3);
+}
+
+pub fn pop_register64bit<'a>(buf: &mut Vec<'a, u8>, reg: Register) {
+    if reg as u8 > 7 {
+        let rex = add_reg_extension(reg, REX);
+        let reg_mod = reg as u8 % 8;
+        buf.extend(&[rex, 0x58 + reg_mod]);
+    } else {
+        buf.push(0x50 + reg as u8);
+    }
+}
+
+pub fn push_register64bit<'a>(buf: &mut Vec<'a, u8>, reg: Register) {
+    if reg as u8 > 7 {
+        let rex = add_reg_extension(reg, REX);
+        let reg_mod = reg as u8 % 8;
+        buf.extend(&[rex, 0x50 + reg_mod]);
+    } else {
+        buf.push(0x50 + reg as u8);
+    }
+}
diff --git a/compiler/gen_dev/src/x86_64/mod.rs b/compiler/gen_dev/src/x86_64/mod.rs
index 1ebc6d6fe7..03dd7d3ee5 100644
--- a/compiler/gen_dev/src/x86_64/mod.rs
+++ b/compiler/gen_dev/src/x86_64/mod.rs
@@ -57,19 +57,15 @@ impl<'a> Backend<'a> for X86_64Backend<'a> {
         // TODO: handle allocating and cleaning up data on the stack.
         let mut out = bumpalo::vec![in self.env.arena];
         if !self.leaf_proc {
-            // push rbp     (0x55)
-            // mov rbp, rsp (0x48, 0x89, 0xE5)
-            out.extend(&[0x55]);
-            asm::mov_register64bit_register64bit(&mut out, Register::RBP, Register::RSP)
+            asm::push_register64bit(&mut out, Register::RBP);
+            asm::mov_register64bit_register64bit(&mut out, Register::RBP, Register::RSP);
         }
         out.extend(&self.buf);
 
         if !self.leaf_proc {
-            // pop rbp
-            out.push(0x5D);
+            asm::pop_register64bit(&mut out, Register::RBP);
         }
-        // ret
-        out.push(0xC3);
+        asm::ret_near(&mut out);
 
         out.into_bump_slice()
     }