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SubjectRe: C undefined behavior fix
On Wed, Jan 02, 2002 at 12:09:10PM -0700, Tom Rini <trini@kernel.crashing.org> wrote:
| On Wed, Jan 02, 2002 at 01:03:25AM +0200, Momchil Velikov wrote:
| > The GCC tries to replace the strcpy from a constant string source with
| > a memcpy, since the length is know at compile time.
|
| 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.

Dudes, maybe I'm missing something here, but why don't you just mark the
source data as volatile? Then it _can't_ assume it knows the length of
the strcpy because it can't assume it knows the content:

If PTRRELOC cast the pointer type to

volatile void *

or something else suitable generic but volatile then this discussion might
not be happening. It would at least move the optimisation into "definite
compiler bug" if it still happens.
--
Cameron Simpson, DoD#743 cs@zip.com.au http://www.zip.com.au/~cs/

I think... Therefore I ride. I ride... Therefore I am.
- Mark Pope <erectus@yarrow.wt.uwa.edu.au>
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