if the base class and the derived class have different alignments, g++
sometimes uses the alignment of the base class for the derived class.
it happens if the source code has definition of a base class instance before
the declaration of the derived class, then the base alignment is used, which is
wrong.
3 files to reproduce the bug:
====================== gcc_align_bug.h ========================
#pragma pack(push, 1)
struct myset_t : public std::set<int>
{
void myadd(int x);
};
#pragma pack(pop)
====================== gcc_align_bug.cpp ======================
#include <set>
#include <stdio.h>
// comment this line to fix the bug. apparently is causes generation of
// wrong code for myset_t:
std::set<int> my_intset;
#include "gcc_align_bug.h"
int main()
{
printf("alignment bug demo\n");
myset_t s;
s.myadd(0); // crash
// NOTREACHED
printf("all ok\n");
return 0;
}
====================== myadd.cpp ======================
#include <set>
#include "gcc_align_bug.h"
//-------------------------------------------------------------------------
void myset_t::myadd(int x)
{
// will crash here:
insert(x);
}
Compile without any options and run:
> g++ gcc_align_bug.cpp myadd.cpp
> ./a.out
alignment bug demo
Segmentation fault
--
Summary: structure alignment for derived class is wrong in some
cases
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: info at hex-rays dot com
GCC build triplet: 4.4.1 - 4.1.3 and probably other builds
GCC host triplet: x86-linux-elf
GCC target triplet: x86-linux-elf
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42158
