Re: kbuild - status on section mismatch warnings

[Ben Dooks <ben-linux@fluff.org>]

On Sun, Mar 05, 2006 at 10:58:53PM +0100, Sam Ravnborg wrote:
> Hi Al.
> 
> > Now try x86 with sd.o non-modular.  And see
> > 
> > 
> > __init foo()
> > {
> > ....
> > 	switch(n) {
> > 	....
> > 	....
> > 	}
> > }
> Hmm, in my tree sd.o has no switch in the init function. But that does
> not change your point which is valid indeed.
> 
> > compiling essentially into
> > 
> > 	if (n < lower || n > upper)
> > 		goto Ldefault;
> > 	addr = const_array_of_labels[n - lower];
> > 	goto addr;
> > 
> > with const_array_of_labels sitting in .rodata and its contents pointing
> > inside foo(), i.e. into .init.text.  And yes, .init.text is discarded,
> > while .rodata is left intact.  Since the only reference to that array
> > disappears along with .init.text *and* section where array goes into is
> > hardwired into gcc, we
> > 	a) are actually OK and
> > 	b) can't do anything about that false positive, AFAICS.
> 
> For the same reason references to .init.text from .rodata are not warned
> upon - there are simply too many compielr generated false positives.
> 
> Following is the original comment from reference_init.pl:
> 
> * Unfortunately references to read only data that referenced .init
> * sections had to be excluded. Almost all of these are false
> * positives, they are created by gcc. The downside of excluding rodata
> * is that there really are some user references from rodata to
> * init code, e.g. drivers/video/vgacon.c:
> *
> * const struct consw vga_con = {
> *        con_startup:            vgacon_startup,
> *
> * where vgacon_startup is __init.  If you want to wade through
> * the false
> * positives, take out the check for rodata.
> 
> And this is unfortunate since we cannot do a full check, but we do a
> better job than before and warn for many of the trivial cases.
> Judging the amount of warnings already generated this is worth checking.

I think the best way to be with an extension to sparse to
check calls from non-init marked code do not to go to items
marked init unless forced to.

-- 
Ben (ben@fluff.org, http://www.fluff.org/)

  'a smiley only costs 4 bytes'