lkml.org 
[lkml]   [2010]   [Nov]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: gcc 4.5.1 / as 2.20.51.0.11 miscompiling drivers/char/i8k.c ?
On Mon, Nov 15, 2010 at 07:30:35PM +0100, Jim Bos wrote:
> On 11/15/2010 07:08 PM, Linus Torvalds wrote:
> > On Mon, Nov 15, 2010 at 9:40 AM, Jim Bos <jim876@xs4all.nl> wrote:
> >>
> >> Hmm, that doesn't work.
> >>
> >> [ Not sure if you read to whole thread but initial workaround was to
> >> change the asm(..) to asm volatile(..) which did work. ]
> >
> > Since I have a different gcc than yours (and I'm not going to compile
> > my own), have you posted your broken .s file anywhere? In fact, with
> > the noinline (and the removal of the "+m" thing - iow just the patch
> > you tried), what does just the "i8k_smm" function assembly look like
> > for you after you've done a "make drivers/char/i8k.s"?
> >
> > If the asm just doesn't exist AT ALL, that's just odd. Because every
> > single call-site of i8k_smm() clearly looks at the return value. So
> > the volatile really shouldn't make any difference from that
> > standpoint. Odd.
> >
> > Linus
> >
>
> Attached version with plain 2.6.36 source and version with the committed
> patch, i.e with the '"+m" (*regs)'

Thanks, this actually helped to see the problem.
The problem is not inside of i8k_smm, which is not inlined, but in the
callers.
ipa-pure-const.c pass thinks i8k_smm is a pure function, thus
regs = {};
regs.eax = 166;
x = i8k_smm (&regs);
if (!x) x = regs.eax;
in the callers is optimized into
regs = {}
regs.eax = 166;
x = i8k_smm (&regs);
if (!x) x = 166;
Now, not sure why this happens, as there is
case GIMPLE_ASM:
for (i = 0; i < gimple_asm_nclobbers (stmt); i++)
{
tree op = gimple_asm_clobber_op (stmt, i);
if (simple_cst_equal(TREE_VALUE (op), memory_identifier_string) == 1)
{
if (dump_file)
fprintf (dump_file, " memory asm clobber is not const/pure");
/* Abandon all hope, ye who enter here. */
local->pure_const_state = IPA_NEITHER;
}
}
Debugging...

Jakub


\
 
 \ /
  Last update: 2010-11-15 20:03    [W:0.630 / U:0.376 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site