Messages in this thread | | | Date | Wed, 2 Jan 2002 21:32:39 -0700 | From | Tom Rini <> | Subject | Re: C undefined behavior fix |
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On Thu, Jan 03, 2002 at 03:08:43PM +1100, Cameron Simpson wrote: > 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:
That's what 3 does.
> 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.
See the rest of the thread for why various people don't like that this doesn't work 'as-is' anymore, and why other people don't like what it's doing period (in C anyhow).
-- Tom Rini (TR1265) http://gate.crashing.org/~trini/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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