Re: [uml-devel] Re: [uml-user] SuSE 9.1 host + 2.4.26 Kernel + GCC 3.3.3 similarities to 2.6.6!?

[BlaisorBlade <blaisorblade_spam@yahoo.it>]

Alle 08:20, martedì 15 giugno 2004, Nix ha scritto:
> On Mon, 14 Jun 2004, BlaisorBlade mused:

> > Well, ok, more hints, the first possible answer to this one seems to be
> > that SuSE enables -funit-at-a-time:
>
> (unsurprising, given that -funit-at-a-time's primary author is jh@suse ;} )

Well, someone following gcc development! Compliments! Do you think, too that 
SuSE gcc is a pre-release or heavily patched?

> Yep, -funit-at-a-time will definitely break kernels that aren't
> expecting it, both because of elision of unused statics and because some
> arches depend on emission of asm's at the top level to emit stuff in the
> same order in generated code, and with -funit-at-a-time this just
> doesn't happen anymore. (I don't think i386 is such an architecture,
> though.)

However, I would like to see a successful test-case with -fno-unit-at-a-time, 
plus understanding what are the faulting declaration (i.e. adding 
attribute_used where needed), before saying this bug is over.

> -funit-at-a-time is enabled by default for C and C++ in GCC 3.4.
>
> > This is the trick:
> The sort of thing you want to stash away in a header file and never lay
> eyes on again. :)

Well, this is already done, in the kernel: see the definition of 
attribute_used in linux/compiler-gcc*.h.

> > static const int hello ATTRIBUTE_USED  = 56;
> >
> > int main()
> > {
> >         asm(
> >         "mov hello, %eax\n"
> >         );
>
> Well, in this *specific* case, hello should be marked as clobbered,

If you mean should be marked by the coder, ok (gcc is not smart).

> which will also stop the compiler eliding it. But this *was* a contrived
> testcase...

Bye!
-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729



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