Translate offsetof in refcount (#255)

Refcount structs don't have the same layout as C structs. Don't
translate offsetof as std::mem::offset_of, instead let clang evaluate
the offset and hardcode it in the generated rust code. ByteRepr takes
care of using it correctly.

Author: lucic71

cpp2rust/converter/models/converter_refcount.cpp

@@ -417,6 +417,14 @@ bool ConverterRefCount::VisitCXXRecordDecl(clang::CXXRecordDecl *decl) {
   return false;
 }
 
+bool ConverterRefCount::VisitOffsetOfExpr(clang::OffsetOfExpr *expr) {
+  clang::Expr::EvalResult result;
+  ENSURE(expr->EvaluateAsInt(result, ctx_));
+  StrCat(std::format("{}_usize", result.Val.getInt().getZExtValue()));
+  computed_expr_type_ = ComputedExprType::FreshValue;
+  return false;
+}
+
 void ConverterRefCount::ConvertOrdAndPartialOrdTraits(
     const clang::CXXRecordDecl *decl, const clang::FunctionDecl *op) {
   std::string first_branch, second_branch, first_return, second_return;

cpp2rust/converter/models/converter_refcount.h

@@ -28,6 +28,8 @@ class ConverterRefCount final : public Converter {
 
   bool VisitCXXRecordDecl(clang::CXXRecordDecl *decl) override;
 
+  bool VisitOffsetOfExpr(clang::OffsetOfExpr *expr) override;
+
   void EmitRustUnion(clang::RecordDecl *decl) override;
 
   bool EmitsReprCForRecords() const override { return false; }

tests/unit/offsetof.cpp

@@ -1,36 +1,37 @@
-// no-compile: refcount
 #include <assert.h>
 #include <stddef.h>
 #include <stdint.h>
+#include <string.h>
 
 struct Layout {
   uint8_t a;
   uint32_t b;
   uint16_t c;
 };
 
-struct Inner {
-  uint16_t x;
-  uint32_t y;
-};
-
-struct Outer {
-  uint8_t pad;
-  struct Inner inner;
+struct Frame {
+  uint16_t tag;
+  char body[64];
 };
 
 int main(void) {
   assert(offsetof(struct Layout, a) == 0);
   assert(offsetof(struct Layout, b) == 4);
   assert(offsetof(struct Layout, c) == 8);
 
-  assert(offsetof(struct Outer, inner.y) == 8);
-
   struct Layout v = {0};
   v.b = 0xDEADBEEF;
   unsigned char *base = (unsigned char *)&v;
   uint32_t *bp = (uint32_t *)(base + offsetof(struct Layout, b));
   assert(*bp == 0xDEADBEEF);
 
+  *(uint32_t *)(base + offsetof(struct Layout, b)) = 0x12345678;
+  assert(v.b == 0x12345678);
+
+  const char *text = "example-body";
+  size_t len = strlen(text) + 1;
+  size_t total = offsetof(struct Frame, body) + len;
+  assert(total == 2 + len);
+
   return 0;
 }

tests/unit/out/refcount/offsetof.rs

@@ -0,0 +1,112 @@
+extern crate libcc2rs;
+use libcc2rs::*;
+use std::cell::RefCell;
+use std::collections::BTreeMap;
+use std::io::prelude::*;
+use std::io::{Read, Seek, Write};
+use std::os::fd::AsFd;
+use std::rc::{Rc, Weak};
+#[derive(Default)]
+pub struct Layout {
+    pub a: Value<u8>,
+    pub b: Value<u32>,
+    pub c: Value<u16>,
+}
+impl Clone for Layout {
+    fn clone(&self) -> Self {
+        let mut this = Self {
+            a: Rc::new(RefCell::new((*self.a.borrow()))),
+            b: Rc::new(RefCell::new((*self.b.borrow()))),
+            c: Rc::new(RefCell::new((*self.c.borrow()))),
+        };
+        this
+    }
+}
+impl ByteRepr for Layout {
+    fn byte_size() -> usize {
+        12
+    }
+    fn to_bytes(&self, buf: &mut [u8]) {
+        (*self.a.borrow()).to_bytes(&mut buf[0..1]);
+        (*self.b.borrow()).to_bytes(&mut buf[4..8]);
+        (*self.c.borrow()).to_bytes(&mut buf[8..10]);
+    }
+    fn from_bytes(buf: &[u8]) -> Self {
+        Self {
+            a: Rc::new(RefCell::new(<u8>::from_bytes(&buf[0..1]))),
+            b: Rc::new(RefCell::new(<u32>::from_bytes(&buf[4..8]))),
+            c: Rc::new(RefCell::new(<u16>::from_bytes(&buf[8..10]))),
+        }
+    }
+}
+#[derive()]
+pub struct Frame {
+    pub tag: Value<u16>,
+    pub body: Value<Box<[u8]>>,
+}
+impl Clone for Frame {
+    fn clone(&self) -> Self {
+        let mut this = Self {
+            tag: Rc::new(RefCell::new((*self.tag.borrow()))),
+            body: Rc::new(RefCell::new((*self.body.borrow()).clone())),
+        };
+        this
+    }
+}
+impl Default for Frame {
+    fn default() -> Self {
+        Frame {
+            tag: <Value<u16>>::default(),
+            body: Rc::new(RefCell::new(
+                (0..64).map(|_| <u8>::default()).collect::<Box<[u8]>>(),
+            )),
+        }
+    }
+}
+impl ByteRepr for Frame {
+    fn byte_size() -> usize {
+        66
+    }
+    fn to_bytes(&self, buf: &mut [u8]) {
+        (*self.tag.borrow()).to_bytes(&mut buf[0..2]);
+        (*self.body.borrow()).to_bytes(&mut buf[2..66]);
+    }
+    fn from_bytes(buf: &[u8]) -> Self {
+        Self {
+            tag: Rc::new(RefCell::new(<u16>::from_bytes(&buf[0..2]))),
+            body: Rc::new(RefCell::new(<Box<[u8]>>::from_bytes(&buf[2..66]))),
+        }
+    }
+}
+pub fn main() {
+    std::process::exit(main_0());
+}
+fn main_0() -> i32 {
+    assert!((0_usize == 0_usize));
+    assert!((4_usize == 4_usize));
+    assert!((8_usize == 8_usize));
+    let v: Value<Layout> = Rc::new(RefCell::new(Layout {
+        a: Rc::new(RefCell::new(0_u8)),
+        b: Rc::new(RefCell::new(<u32>::default())),
+        c: Rc::new(RefCell::new(<u16>::default())),
+    }));
+    (*(*v.borrow()).b.borrow_mut()) = 3735928559_u32;
+    let base: Value<Ptr<u8>> = Rc::new(RefCell::new((v.as_pointer()).reinterpret_cast::<u8>()));
+    let bp: Value<Ptr<u32>> = Rc::new(RefCell::new(
+        ((*base.borrow()).offset((4_usize) as isize)).reinterpret_cast::<u32>(),
+    ));
+    assert!((((*bp.borrow()).read()) == 3735928559_u32));
+    ((*base.borrow()).offset((4_usize) as isize))
+        .reinterpret_cast::<u32>()
+        .write(305419896_u32);
+    assert!(((*(*v.borrow()).b.borrow()) == 305419896_u32));
+    let text: Value<Ptr<u8>> = Rc::new(RefCell::new(Ptr::from_string_literal(b"example-body")));
+    let len: Value<usize> = Rc::new(RefCell::new(
+        ((*text.borrow()).to_string_iterator().count()).wrapping_add(1_usize),
+    ));
+    let total: Value<usize> = Rc::new(RefCell::new(
+        ((2_usize as u64).wrapping_add(((*len.borrow()) as u64)) as usize),
+    ));
+    assert!(((*total.borrow()) == (2_usize).wrapping_add((*len.borrow()))));
+    return 0;
+}

tests/unit/out/unsafe/offsetof.rs

@@ -14,16 +14,18 @@ pub struct Layout {
     pub c: u16,
 }
 #[repr(C)]
-#[derive(Copy, Clone, Default)]
-pub struct Inner {
-    pub x: u16,
-    pub y: u32,
+#[derive(Copy, Clone)]
+pub struct Frame {
+    pub tag: u16,
+    pub body: [libc::c_char; 64],
 }
-#[repr(C)]
-#[derive(Copy, Clone, Default)]
-pub struct Outer {
-    pub pad: u8,
-    pub inner: Inner,
+impl Default for Frame {
+    fn default() -> Self {
+        Frame {
+            tag: 0_u16,
+            body: [(0 as libc::c_char); 64],
+        }
+    }
 }
 pub fn main() {
     unsafe {
@@ -34,7 +36,6 @@ unsafe fn main_0() -> i32 {
     assert!(((::std::mem::offset_of!(Layout, a)) == (0_usize)));
     assert!(((::std::mem::offset_of!(Layout, b)) == (4_usize)));
     assert!(((::std::mem::offset_of!(Layout, c)) == (8_usize)));
-    assert!(((::std::mem::offset_of!(Outer, inner.y)) == (8_usize)));
     let mut v: Layout = Layout {
         a: 0_u8,
         b: 0_u32,
@@ -45,5 +46,12 @@ unsafe fn main_0() -> i32 {
     let mut bp: *mut u32 =
         ((base.offset((::std::mem::offset_of!(Layout, b)) as isize)) as *mut u32);
     assert!(((*bp) == (3735928559_u32)));
+    (*((base.offset((::std::mem::offset_of!(Layout, b)) as isize)) as *mut u32)) = 305419896_u32;
+    assert!(((v.b) == (305419896_u32)));
+    let mut text: *const libc::c_char = c"example-body".as_ptr();
+    let mut len: usize = (libc::strlen(text)).wrapping_add(1_usize);
+    let mut total: usize =
+        ((::std::mem::offset_of!(Frame, body) as u64).wrapping_add((len as u64)) as usize);
+    assert!(((total) == ((2_usize).wrapping_add(len))));
     return 0;
 }