alloca busted (Was: HEADS UP: macppc gcc8 fallout in -current)

On Wed, Jan 01, 2020 at 23:55:36 +0300, Valery Ushakov wrote:

> I have upgraded my test mac mini g4 to current from Dec 22 but got
> around to compile something on it last night only and it looks like
> gcc8 is busted (powerpc ports were switched on Dec 14).
> 
> $ cc --version | sed 1q
> cc (nb1 20190930) 8.3.0
> $ cat main.c
> int main() { return 0; }
> $ /usr/libexec/cc1 main.c
> <built-in>: internal compiler error: Segmentation fault
> 
> Can do much debugging either as gdb seems busted too
> 
> $ gdb
> Undefined save command: "tracepoints".  Try "help save".

It looks like alloca() is busted in gcc8.  I traced that gdb problem
to memory corruption caused by broken alloca.  My bet is that the gcc
problem has the same cause.

-uwe