http://llvm.org/bugs/show_bug.cgi?id=18826
Bug ID: 18826
Summary: MS ABI: clang doesn't create a packed struct when one
is required
Product: clang
Version: unspecified
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: LLVM Codegen
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
consider:
extern "C" int printf(const char *, ...);
char buffer[1 << 10];
struct A {
A() {
printf("A : %u\n", (char *)this - buffer);
}
};
struct B {
bool BField;
B() {
printf("B : %u\n", (char *)this - buffer);
printf("BField : %u\n", (char *)&BField - buffer);
}
};
struct C : virtual A, virtual B {
bool CField;
C() {
printf("C : %u\n", (char *)this - buffer);
printf("CField : %u\n", (char *)&CField - buffer);
printf("A-in-C : %u\n", (char *)(A *)this - buffer);
printf("B-in-C : %u\n", (char *)(B *)this - buffer);
}
};
struct D : C, A {
D() {
printf("D : %u\n", (char *)this - buffer);
printf("C-in-D : %u\n", (char *)(C *)this - buffer);
}
};
void *operator new(size_t, void *pv) { return buffer; }
int main() {
printf("sizeof(A): %u\n", sizeof(A));
printf("sizeof(B): %u\n", sizeof(B));
printf("sizeof(C): %u\n", sizeof(C));
printf("sizeof(D): %u\n", sizeof(D));
new (buffer) D;
}
clang gives us:
sizeof(A): 1
sizeof(B): 1
sizeof(C): 9
sizeof(D): 13
A : 12
B : 12
BField : 12
C : 0
CField : 4
A-in-C : 12
B-in-C : 12
A : 9
D : 0
C-in-D : 0
msvc gives us:
sizeof(A): 1
sizeof(B): 1
sizeof(C): 9
sizeof(D): 9
A : 8
B : 8
BField : 8
C : 0
CField : 4
A-in-C : 8
B-in-C : 8
A : 8
D : 0
C-in-D : 0
C's nvsize is 8 in clang
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