On Fri, May 02, 2008 at 03:57:08PM +0200, Sam Ravnborg wrote:
quoted text
> OK, can anyone confirm that this fails to build which a
> buggy gcc:
> 
> 
> void __attribute__((weak)) func(void)
> {
>     /* no code */
> }
> 
> int main()
> {
>     func();
>     return 0;
> }

Of course it doesn't fail to build.  With buggy gcc it will be optimized
to
void __attribute__((weak)) func (void)
{
}

int main ()
{
  return 0;
}

(similarly how all recent gccs optimize this without the weak attribute)
while non-buggy gcc keeps the func call.
So, you either need to grep the assembly (that's what e.g. the GCC testcase
does), or you can e.g. use a runtime testcase:
extern void abort (void);
void __attribute__((weak)) func (void) { }
int main () { func (); abort (); }
in one compilation unit and
extern void exit (int);
void func (void) { exit (0); }
in another one.  I doubt a runtime testcase is acceptable though for the
kernel, as the cross compiler used to build the kernel might not be able to
create userland executables (missing C library, etc.).

	Jakub
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