Comment 1 for bug 1262380

This looks like an issue with passing structs by value. g_cclosure_marshal_VOID__PARAM is only allocating a 64 byte stack frame and is calling signal_normal via some marshalling tricks. The prototype for signal_normal includes a large struct which will be partially passed in registers and signal_normal expects to be able to write that out to the parameter save area in the callers frame.

signal_normal does end up writing out parameters to the caller stack:

Dump of assembler code for function signal_normal:
   0x000000001000c880 <+0>: lis r2,4099
   0x000000001000c884 <+4>: addi r2,r2,-4080
   0x000000001000c888 <+8>: mflr r0
   0x000000001000c88c <+12>: std r31,-8(r1)
   0x000000001000c890 <+16>: mr r31,r3
   0x000000001000c894 <+20>: std r0,16(r1)
   0x000000001000c898 <+24>: stdu r1,-48(r1)
   0x000000001000c89c <+28>: std r4,88(r1)
   0x000000001000c8a0 <+32>: std r5,96(r1)
   0x000000001000c8a4 <+36>: std r6,104(r1)
   0x000000001000c8a8 <+40>: std r7,112(r1)
   0x000000001000c8ac <+44>: std r8,120(r1)
   0x000000001000c8b0 <+48>: std r9,128(r1)
   0x000000001000c8b4 <+52>: std r10,136(r1)

And since g_cclosure_marshal_VOID__PARAM hasn't allocated enough stack we stomp all over the stack and die.

What is interesting is that signal_normal doesn't touch the struct, so why are we bothering to save it? It looks like a missing optimisation in gcc and this test case shows it:

struct foo
{
  void *a, *b, *c, *d, *e, *f, *g, *h;
#if 1
  void *i;
#endif
};

int bar(struct foo foo)
{
        return 0;
}

With a struct big enough to not fit into registers, we always save the whole struct out to the stack even if we never touch it:

bar:
        std 3,32(1)
        std 4,40(1)
        li 3,0
        std 5,48(1)
        std 6,56(1)
        std 7,64(1)
        std 8,72(1)
        std 9,80(1)
        std 10,88(1)
        blr