Re: [PATCH] C undefined behavior fix

From: Tom Rini (
Date: Wed Jan 02 2002 - 15:42:21 EST

On Wed, Jan 02, 2002 at 12:13:34PM -0800, Joe Buck wrote:
> > Okay, here's a summary of all of the options we have:
> > 1) Change this particular strcpy to a memcpy
> > 2) Add -ffreestanding to the CFLAGS of arch/ppc/kernel/prom.o (If this
> > optimization comes back on with this flag later on, it would be a
> > compiler bug, yes?)
> > 3) Modify the RELOC() marco in such a way that GCC won't attempt to
> > optimize anything which touches it [1]. (Franz, again by Jakub)
> > 4) Introduce a function to do the calculations [2]. (Corey Minyard)
> > 5) 'Properly' set things up so that we don't need the RELOC() macros
> > (-mrelocatable or so?), and forget this mess altogether.
> 2) will prevent any future gcc from ever assuming it can transform the
> strcpy into anything but a call to strcpy, or assume anything about the
> semantics of strcpy.

If we go with this, it also might make sense to split all of the
{PTR,UN,}RELOC() macro users into a different file or split up btext.c a
bit more, just to be safe.

> Be careful with 3), as trying to fool the optimizer
> is likely to be only a temporary solution (meaning that the kernel people
> will return to flame the gcc people when the optimizer gets changed
> again).

Well, it's one of those changes that really should stop gcc, unless
there's a bug on the gcc side, if I read the patch/comments about it

Tom Rini (TR1265)
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