egcs-1.1.2 ping bug also causes miscompilation of pcbit isdn driver
dinon (dinon@csie.ncu.edu.tw)
Thu, 17 Jun 1999 17:15:49 +0800 (CST)
On Wed, 16 Jun 1999 owner-linux-kernel-digest@vger.rutgers.edu wrote:
>
> On 13 Jun 1999 16:47:26 +0200, Lars Heete wrote:
>
> >Hello,
> >
> >the bug in egcs-1.1.2 that causes miscompilations of in_cksum also is
> >responsible for the pcbit-isdn driver failure (See thread "Still no ISDN
> >connection"). I suspect there are some other places in kernel
> >which suffer from this bug.
> >
> >--------------------- test case ----------------------
> >#include <stdio.h>
> >int main(int argc, char **argv) {
> > struct {char c1, c2, c2, 4;} t;
> > t.c4 = 0x78; t.c3 = 0x56; t.c2 = 0x34; t.c1 = 0x12;
> > printf("0x%x\n", *((unsigned long*) &t));
> > return 0;
> >}
> >
> >gives 0x12 with egcs-1.1.2 on i386, instead of 0x78563412.
> >
try the modifier volatile
#include <stdio.h>
#ifdef USE_VOLATILE
#define VOLATILE volatile
#else
#define VOLATILE
#endif
int main(int argc, char **argv)
{
VOLATILE struct {char c1, c2, c3, c4;} t;
t.c4 = 0x78; t.c3 = 0x56; t.c2 = 0x34; t.c1 = 0x12;
printf("0x%x\n", *((unsigned long*) &t));
return 0;
}
if USE_VOLATILE is defined, then the result will be 0x78563412,
otherwise 0x12, whether -fstrict-aliasing is used.
So, I think maybe egcs over-optimizes in this case.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/