[LLVMbugs] [Bug 18610] New: ABI incompatibility with GCC regarding aligned virtual base

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=18610

            Bug ID: 18610
           Summary: ABI incompatibility with GCC regarding aligned virtual
                    base
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: david.majnemer at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

We place an aligned virtual base at an offset which is not a multiple of it's
alignment.

consider:
extern "C" int printf(const char *, ...);
struct A {};
struct __attribute__((aligned(16))) B : A {};
#pragma pack(push, 8)
struct C : virtual B, A {};
#pragma pack(pop)
int main() {
  printf("sizeof(C): %zu\n", sizeof(C));
}

compile with:
~/llvm/build/bin/clang++ -cc1 -triple x86_64-unknown-linux-gnu different.cpp -o
clang_test

clang gives us 24
gcc gives us 32


also:
$ ~/llvm/build/bin/clang++ -cc1 different.cpp -fdump-record-layouts
-emit-llvm-only
*** Dumping AST Record Layout
   0 | struct A (empty)
     | [sizeof=1, dsize=1, align=1
     |  nvsize=1, nvalign=1]


*** Dumping AST Record Layout
   0 | struct B (empty)
   0 |   struct A (base) (empty)
     | [sizeof=16, dsize=0, align=16
     |  nvsize=1, nvalign=16]


*** Dumping AST Record Layout
   0 | struct C
   0 |   (C vtable pointer)
   0 |   struct A (base) (empty)
   8 |   struct B (virtual base) (empty)
   8 |     struct A (base) (empty)
     | [sizeof=24, dsize=8, align=8
     |  nvsize=8, nvalign=8]

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20140125/c1660c42/attachment.html>