From 10b7f6d581f04b284a8308d4c1c82a59dae36a6b Mon Sep 17 00:00:00 2001
From: iximeow <me@iximeow.net>
Date: Wed, 15 Jan 2020 20:20:55 -0800
Subject: avoid needing to dynamically allocate in yaxpeax-x86 ffi

this makes ffi builds also no-std, and significantly smaller too
---
 ffi/src/lib.rs | 64 ++++++++++++++++++++++++++++++++++------------------------
 1 file changed, 38 insertions(+), 26 deletions(-)

diff --git a/ffi/src/lib.rs b/ffi/src/lib.rs
index 12e077b..9d726d2 100644
--- a/ffi/src/lib.rs
+++ b/ffi/src/lib.rs
@@ -1,43 +1,55 @@
-use yaxpeax_arch::{Arch, Decoder, LengthedInstruction, Address};
+#![no_std]
+#![feature(lang_items)]
+
+#[panic_handler]
+#[cold]
+fn panic(panic: &core::panic::PanicInfo) -> ! {
+    loop {}
+}
+
+#[lang = "eh_personality"] extern fn eh_personality() {}
+
+use yaxpeax_arch::{Arch, Decoder, LengthedInstruction, Address, AddressBase};
 use yaxpeax_x86::x86_64;
 
-use std::fmt::Write;
+use core::fmt::Write;
 
 #[no_mangle]
-pub unsafe extern "C" fn yaxpeax_decode_x86_64_optimistic(data: *const std::os::raw::c_char, length: std::os::raw::c_longlong, inst: *mut yaxpeax_x86::Instruction) -> bool {
-    let inst: &mut yaxpeax_x86::Instruction = std::mem::transmute(inst);
-    <x86_64 as Arch>::Decoder::default().decode_into(inst, std::slice::from_raw_parts(data as *const u8, length as usize).iter().cloned()).is_err()
+pub unsafe extern "C" fn yaxpeax_decode_x86_64_optimistic(data: *const u8, length: u64, inst: *mut yaxpeax_x86::Instruction) -> bool {
+    let inst: &mut yaxpeax_x86::Instruction = core::mem::transmute(inst);
+    <x86_64 as Arch>::Decoder::default().decode_into(inst, core::slice::from_raw_parts(data as *const u8, length as usize).iter().cloned()).is_err()
 }
 
 #[no_mangle]
 pub unsafe extern "C" fn yaxpeax_instr_length_x86_64(inst: *mut yaxpeax_x86::Instruction) -> usize {
-    let inst: &mut yaxpeax_x86::Instruction = std::mem::transmute(inst);
+    let inst: &mut yaxpeax_x86::Instruction = core::mem::transmute(inst);
     inst.len().to_linear()
 }
 
-#[no_mangle]
-pub unsafe extern "C" fn yaxpeax_instr_fmt(inst: *mut yaxpeax_x86::Instruction, size: *mut u64, capacity: *mut u64) -> *mut u8 {
-    let inst: &mut yaxpeax_x86::Instruction = std::mem::transmute(inst);
-    let mut res = String::with_capacity(128);
-
-    write!(res, "{}", inst).unwrap();
-
-    let mut bytes = res.into_bytes();
-    let ptr = bytes.as_mut_ptr();
-    *capacity = bytes.capacity() as u64;
-    *size = bytes.len() as u64;
-    std::mem::forget(bytes);
-    ptr
+struct InstructionSink<'buf> {
+    buf: &'buf mut [u8],
+    offs: usize,
 }
 
-#[no_mangle]
-pub unsafe extern "C" fn yaxpeax_instr_x86_64_blank() -> *mut yaxpeax_x86::Instruction {
-    Box::leak(Box::new(yaxpeax_x86::Instruction::invalid()))
+impl<'a> core::fmt::Write for InstructionSink<'a> {
+    fn write_str(&mut self, s: &str) -> core::fmt::Result {
+        for b in s.bytes() {
+            if self.offs < self.buf.len() {
+                self.buf[self.offs] = b;
+                self.offs += 1;
+            } else {
+                break;
+            }
+        }
+
+        Ok(())
+    }
 }
 
 #[no_mangle]
-pub unsafe extern "C" fn yaxpeax_str_drop(data: *mut u8, size: u64, capacity: u64) {
-    std::mem::drop(
-        Vec::from_raw_parts(data, size as usize, capacity as usize)
-    );
+pub unsafe extern "C" fn yaxpeax_instr_fmt(inst: *mut yaxpeax_x86::Instruction, text: *mut u8, len: usize) {
+    let inst: &mut yaxpeax_x86::Instruction = core::mem::transmute(inst);
+    let mut res = core::slice::from_raw_parts_mut(text, len);
+
+    write!(InstructionSink { buf: res, offs: 0 }, "{}", inst).unwrap();
 }
-- 
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