From 8316b628bbc9945fd1d08305317cf49a6482801f Mon Sep 17 00:00:00 2001
From: Johannes Stoelp <johannes.stoelp@gmail.com>
Date: Sun, 5 Mar 2023 22:20:48 +0100
Subject: Added CALL and call extern fn example

---
 examples/add.rs  | 30 ++++++++++++++++++++++++++++++
 src/insn.rs      |  6 ++++++
 src/insn/call.rs |  7 +++++++
 src/prelude.rs   |  2 +-
 src/rt.rs        |  3 ++-
 5 files changed, 46 insertions(+), 2 deletions(-)
 create mode 100644 examples/add.rs
 create mode 100644 src/insn/call.rs

diff --git a/examples/add.rs b/examples/add.rs
new file mode 100644
index 0000000..ef010b6
--- /dev/null
+++ b/examples/add.rs
@@ -0,0 +1,30 @@
+use juicebox_asm::prelude::*;
+use juicebox_asm::Runtime;
+use Reg64::*;
+
+extern "C" fn add(a: u32, b: u32) -> u32 {
+    a + b
+}
+
+fn main() {
+    let mut asm = Asm::new();
+
+    // SystemV abi:
+    //   rdi -> first argument
+    //   rsi -> second argument
+    //   rax -> return value
+    //
+    asm.mov(rsi, Imm64::from(42));
+    asm.mov(rax, Imm64::from(add as u64));
+    asm.call(rax);
+    asm.ret();
+
+    let code = asm.into_code();
+    std::fs::write("jit.asm", &code).unwrap();
+
+    let rt = Runtime::new(&code);
+    let add42 = unsafe { rt.as_fn::<extern "C" fn(u32) -> u32>() };
+
+    let res = add42(5);
+    assert_eq!(res, 47);
+}
diff --git a/src/insn.rs b/src/insn.rs
index 2a6ca42..8810085 100644
--- a/src/insn.rs
+++ b/src/insn.rs
@@ -1,6 +1,7 @@
 //! Trait definitions of various instructions.
 
 mod add;
+mod call;
 mod dec;
 mod jmp;
 mod jnz;
@@ -15,6 +16,11 @@ pub trait Add<T, U> {
     fn add(&mut self, op1: T, op2: U);
 }
 
+pub trait Call<T> {
+    /// Emit a call instruction.
+    fn call(&mut self, op1: T);
+}
+
 pub trait Dec<T> {
     /// Emit a decrement instruction.
     fn dec(&mut self, op1: T);
diff --git a/src/insn/call.rs b/src/insn/call.rs
new file mode 100644
index 0000000..8a71db8
--- /dev/null
+++ b/src/insn/call.rs
@@ -0,0 +1,7 @@
+use crate::prelude::*;
+
+impl Call<Reg64> for Asm {
+    fn call(&mut self, op1: Reg64) {
+        self.encode_r(0xff, 0x2, op1);
+    }
+}
diff --git a/src/prelude.rs b/src/prelude.rs
index 0093240..b21d67c 100644
--- a/src/prelude.rs
+++ b/src/prelude.rs
@@ -7,4 +7,4 @@ pub use crate::imm::{Imm16, Imm32, Imm64, Imm8};
 pub use crate::label::Label;
 pub use crate::reg::{Reg16, Reg32, Reg64, Reg8};
 
-pub use crate::insn::{Add, Dec, Jmp, Jnz, Jz, Mov, Test};
+pub use crate::insn::{Add, Call, Dec, Jmp, Jnz, Jz, Mov, Test};
diff --git a/src/rt.rs b/src/rt.rs
index 1e9289e..7b5f74b 100644
--- a/src/rt.rs
+++ b/src/rt.rs
@@ -11,7 +11,7 @@ pub struct Runtime {
 
 impl Runtime {
     /// Create a new [Runtime].
-    pub fn new(code: &[u8]) -> Runtime {
+    pub fn new(code: impl AsRef<[u8]>) -> Runtime {
         // Allocate a single page.
         let len = core::num::NonZeroUsize::new(4096).unwrap();
         let buf = unsafe {
@@ -27,6 +27,7 @@ impl Runtime {
         };
         {
             // Copy over code.
+            let code = code.as_ref();
             assert!(code.len() < len.get());
             unsafe { std::ptr::copy_nonoverlapping(code.as_ptr(), buf.cast(), len.get()) };
         }
-- 
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