[PATCH] Set behavior of sprintf-like functions with overlapping source and destination

[Paul Eggert]

Dumb question: if fortification is enabled, why can't sprintf-like 
functions report an error when the source and destination overlap? The 
point of fortification is to catch and report undefined behavior when 
it's easy, as is the case here.

> /* Test the sprintf (buf, "%s", buf) does not override buf.

I'm leery of adding this test case, as it tests undefined behavior that 
the glibc manual does not document as an extension (and it shouldn't be 
documented either).

Traditionally we didn't worry about breaking code like PughUtils.c's 
'sprintf(mess,"%s %d",mess,...)' under the principle that such code was 
already broken. Why depart from that tradition here?