When cross-compiling kernel/signal.c from the Linux kernel for Vax on an i686
Linux PC the assembler crashes with memory corruption reported by libc. Using
libefence turns the error into a segmentation fault.

The error is caused by lines 550-552 in app.c. If the from-buffer contains more
text than the space left in the to-buffer to ends up pointing after the buffer,
and the next call of PUT writes beyond the end.

To fix the problem something like the attached patch could be used - it just
copies the check from PUT.