[TUHS] tool (that wnj wrote?) that reduced the data segment size?

Norman Wilson norman at oclsc.org
Sun Nov 29 09:30:53 AEST 2015

I'm too tired to dig for the exact words in the ISO standard,
but I had the impression that the official C rule these days
is that the effect of writing on a string literal is undefined.

So it's legal for an implementation to make strings read-only,
or to point several references to "What's the recipe today, Jim"
to one copy of the stripng in memory, and even to point uses of
"Jim" to the tail of the same string.  Or both.

It is also legal for every string literal to reside in its own
memory and to be writable, but since the effect is undefined,
code that relies on that is on thin ice, especially if meant to
be portable code.

I have used, and even fixed (unrelated) bugs in, a compiler
that merged identical strings.  I forget whether it also looked
for suffix matches.  Whether the strings went in read-only
memory was up to the code generator (of course); in the new
back-end I wrote for it, I made them so.  This turned up quite a
few fumbles in very-old UNIX code that assumed unique, writable
string literals, especially those that called mktemp(3).  To my
mind that just meant the programs needed to be fixed to match
current standards (just as many old programs needed fixes to
compile without error in ISO C), so I fixed them.

I didn't (and still don't) like Joy's heavy-handed hack, but I
see his point, and think it's just fine for the language rules
to allow the compiler to do it hacklessly.

Norman Wilson
Toronto ON

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