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

[uml <uml@dot1q.net>]

Oops, I tried this the other day at the beginning of this thread -- it
worked great for me.

I'm afraid I just don't know enough about lower level compiling options or
gcc have ever diagnosed this myself; however, I don't mind recompiling a
kernel 100 times to see what works -- or doesn't. (=

Thanks!


----- Original Message ----- 
From: "BlaisorBlade" <blaisorblade_spam@yahoo.it>
To: "Nix" <nix@esperi.org.uk>
Cc: "uml" <uml@dot1q.net>; "roland" <for_spam@gmx.de>; "uml-user"
<user-mode-linux-user@lists.sourceforge.net>;
<user-mode-linux-devel@lists.sourceforge.net>
Sent: Wednesday, June 16, 2004 3.09 PM
Subject: Re: [uml-devel] Re: [uml-user] SuSE 9.1 host + 2.4.26 Kernel + GCC
3.3.3 similarities to 2.6.6!?


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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