Discovered as a failure of GDB test:
FAIL: gdb.base/stack-checking.exp: continue to breakpoint: breakpoint for big frame

With current SVN head @144426:

/* t.c */
void foo() { char buf[524188]; }
int main() { foo(); return 0; }

i686-unknown-linux-gnu-gcc t.c -fstack-check && ./a.out
Segmentation fault

AFAICT, this is a regression from 4.3.1
Problem also happens in x86_64-unknown-linux-gnu.
Minimal size to crash appears to be about 57058.