Hi all, I have recently met a segfault in a program I had to port from x86 to ARMv7. After some investigation I managed to narrow it down to a few C++ lines which when compiled with -O > 0 will always produce an incorrect assembly on ARM. I am using GCC 4.2.1 for ARM. The register R1 holding the pointer to the construction vtable for the Parent-in-Child is actually pointing to the wrong Parent-in-Child vtable: Let's assume we have a virtual base class A, two derived class B and C virtually inheriting from A and a final class D derived from B and C. When instantiating D, the CTOR for B is called with R1 pointing to the construction vtable for C-in-D instead of the one for B-in-D, which thus make the program crash since it tries to access an uninitialized element of the vtable for C when trying to access elements in B. (I hope it is clear enough). When compiling with the -fno-toplevel-reorder, the issue disappear since the CTORs are called in the correct order and with their corresponding construction vtable. Compiling with -fno-unit-at-a-time also fixes the problem, but it is deprecated according to GCC documentation. Disabling inlining also works obviously. It seems to be related to bug: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41354 however the -fno-tree-sink doesn't resolve the issue, so I am assuming that it is not a duplicate. Since the code seems legit from an ISO C++ point of view, I assume that GCC is doing something wrong when inlining some CTORs. Can you guys confirm me that ? Here is a sample code: class A { public: ~A() {} virtual int e() = 0; }; class B : virtual public A { public: ~B() {} virtual int f() = 0; }; class C : virtual public A { public: ~C(); C(int a); protected: int _c; virtual int e(); }; class D : public C, virtual public B { public: ~D(); D(int a); virtual int f(); }; C::C(int a) { _c = a; } C::~C() {} int C::e() { return _c; } D::D(int a):C(a) { } D::~D() {} int D::f() { return _c+1; } int main() { D* d = new D(1); } Here is GDB analysis: Program received signal SIGSEGV, Segmentation fault. 0x00008530 in C::C () (gdb) disas Dump of assembler code for function C::C(int): 0x00008524 <C::C(int)+0>: push {lr} ; (str lr, [sp, #-4]!) 0x00008528 <C::C(int)+4>: ldr r3, [r1] 0x0000852c <C::C(int)+8>: str r3, [r0] 0x00008530 <C::C(int)+12>: ldr lr, [r3, #-16] 0x00008534 <C::C(int)+16>: ldr r3, [r1, #4] 0x00008538 <C::C(int)+20>: str r3, [r0, lr] 0x0000853c <C::C(int)+24>: str r2, [r0, #4] 0x00008540 <C::C(int)+28>: pop {pc} ; (ldr pc, [sp], #4) End of assembler dump. (gdb) disas $r1 Dump of assembler code for function construction vtable for B-in-D: Regards, -- ender
