Translate offsetof (#186)

Author: lucic71

cpp2rust/converter/converter.cpp

@@ -3052,6 +3052,24 @@ bool Converter::VisitTypeTraitExpr(clang::TypeTraitExpr *expr) {
   return false;
 }
 
+bool Converter::VisitOffsetOfExpr(clang::OffsetOfExpr *expr) {
+  std::string member_path;
+  for (unsigned i = 0; i < expr->getNumComponents(); ++i) {
+    const clang::OffsetOfNode &node = expr->getComponent(i);
+    ENSURE(node.getKind() == clang::OffsetOfNode::Field);
+    if (!member_path.empty()) {
+      member_path += '.';
+    }
+    member_path += GetNamedDeclAsString(node.getField());
+  }
+  StrCat(
+      std::format("::std::mem::offset_of!({}, {}) as u64",
+                  GetUnsafeTypeAsString(expr->getTypeSourceInfo()->getType()),
+                  member_path));
+  computed_expr_type_ = ComputedExprType::FreshValue;
+  return false;
+}
+
 bool Converter::VisitEnumDecl(clang::EnumDecl *decl) {
   ENSURE(decl_ids_.insert(GetID(decl)).second);
   if (Mapper::Contains(ctx_.getCanonicalTagType(decl))) {

cpp2rust/converter/converter.h

@@ -349,6 +349,8 @@ class Converter : public clang::RecursiveASTVisitor<Converter> {
 
   virtual bool VisitTypeTraitExpr(clang::TypeTraitExpr *expr);
 
+  virtual bool VisitOffsetOfExpr(clang::OffsetOfExpr *expr);
+
   virtual bool VisitEnumDecl(clang::EnumDecl *decl);
 
   virtual void AddFromImpl(clang::EnumDecl *decl);

tests/unit/offsetof.cpp

@@ -0,0 +1,36 @@
+// no-compile: refcount
+#include <assert.h>
+#include <stddef.h>
+#include <stdint.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;
+};
+
+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);
+
+  return 0;
+}

tests/unit/out/unsafe/offsetof.rs

@@ -0,0 +1,49 @@
+extern crate libc;
+use libc::*;
+extern crate libcc2rs;
+use libcc2rs::*;
+use std::collections::BTreeMap;
+use std::io::{Read, Seek, Write};
+use std::os::fd::{AsFd, FromRawFd, IntoRawFd};
+use std::rc::Rc;
+#[repr(C)]
+#[derive(Copy, Clone, Default)]
+pub struct Layout {
+    pub a: u8,
+    pub b: u32,
+    pub c: u16,
+}
+#[repr(C)]
+#[derive(Copy, Clone, Default)]
+pub struct Inner {
+    pub x: u16,
+    pub y: u32,
+}
+#[repr(C)]
+#[derive(Copy, Clone, Default)]
+pub struct Outer {
+    pub pad: u8,
+    pub inner: Inner,
+}
+pub fn main() {
+    unsafe {
+        std::process::exit(main_0() as i32);
+    }
+}
+unsafe fn main_0() -> i32 {
+    assert!(((::std::mem::offset_of!(Layout, a) as u64) == (0_u64)));
+    assert!(((::std::mem::offset_of!(Layout, b) as u64) == (4_u64)));
+    assert!(((::std::mem::offset_of!(Layout, c) as u64) == (8_u64)));
+    assert!(((::std::mem::offset_of!(Outer, inner.y) as u64) == (8_u64)));
+    let mut v: Layout = Layout {
+        a: 0_u8,
+        b: 0_u32,
+        c: 0_u16,
+    };
+    v.b = 3735928559_u32;
+    let mut base: *mut u8 = ((&mut v as *mut Layout) as *mut u8);
+    let mut bp: *mut u32 =
+        ((base.offset((::std::mem::offset_of!(Layout, b) as u64) as isize)) as *mut u32);
+    assert!(((*bp) == (3735928559_u32)));
+    return 0;
+}