https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111742
Bug ID: 111742
Summary: Misaligned generated code with MI using aligned
virtual base
Product: gcc
Version: 13.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: cuzdav at gmail dot com
Target Milestone: ---
Generated code is misaligned (and crashes in slightly more complex code), in
trunk all the way back to gcc 8.1, when built in c++11 or higher, with O3.
(Linux, x86)
Complete code:
//////////////////////////////////////////
struct X {
void * a = nullptr;
void * b = nullptr;
};
struct alignas(16) AlignedData { };
struct A : virtual AlignedData {
X xxx;
};
struct B : virtual AlignedData {};
struct Test : B, A {};
Test* t = new Test;
int main() {}
//////////////////////////////////////////
Compiler Explorer demo:
https://godbolt.org/z/aodTdaedW
Running with UB-san reports this:
/app/example.cpp:14:8: runtime error: constructor call on misaligned address
0x00000227f2b8 for type 'struct A', which requires 16 byte alignment
0x00000227f2b8: note: pointer points here
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00
^
/app/example.cpp:8:8: runtime error: member access within misaligned address
0x00000227f2b8 for type 'struct A', which requires 16 byte alignment
0x00000227f2b8: note: pointer points here
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00
^
