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SubjectRe: [patch 07/18] v4l: nopage

* Andrew Morton <akpm@linux-foundation.org> wrote:

> On Wed, 05 Dec 2007 18:15:54 +1100
> npiggin@suse.de wrote:
>
> > +static int
> > +videobuf_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> > {
> > struct page *page;
> >
> > - dprintk(3,"nopage: fault @ %08lx [vma %08lx-%08lx]\n",
> > - vaddr,vma->vm_start,vma->vm_end);
> > - if (vaddr > vma->vm_end)
> > - return NOPAGE_SIGBUS;
> > + dprintk(3,"fault: fault @ %08lx [vma %08lx-%08lx]\n",
> > + (unsigned long)vmf->virtual_address,vma->vm_start,vma->vm_end);
> > page = alloc_page(GFP_USER | __GFP_DMA32);
> > if (!page)
> > - return NOPAGE_OOM;
> > + return VM_FAULT_OOM;
> > clear_user_page(page_address(page), vaddr, page);
>
> This didn't compile on sparc64 because `vaddr' is undefined.
>
>
> Let us see why:
>
> #define clear_user_page(page, vaddr, pg) clear_page(page)
> #define copy_user_page(to, from, vaddr, pg) copy_page(to, from)
>
> #define __alloc_zeroed_user_highpage(movableflags, vma, vaddr) \
> alloc_page_vma(GFP_HIGHUSER | __GFP_ZERO | movableflags, vma, vaddr)
>
> root cause: lack of argument checking on x86 due to stupid macros.
>
>
> Could someone *please* start a little project of extirpating this
> utter brain damage? Convert those macros to typechecked static
> inlines on x86 (at least) so this sort of thing (which happens again
> and again and again) is lessened?

i wanted to write a reply to suggest a checkpatch policy for this. When
i noticed this sentence at the end of your mail:

> macros are such miserable things. I wonder if we could get checkpatch
> to help out here?

/me too :-)

any policy that gets into checkpatch.pl's default output is a policy for
arch/x86 patch merging. (as long as it's not a false positive) And
because we do all these unifications the effects of checkpatch.pl
permeate basically every aspect of arch/x86.

one approach would be to make new macros in include/* a no-no. That
would hurt a few of the legitimate uses though, so maybe a useful
refinement would be to check the structure of macros: are arguments used
twice (side-effect), are arguments unused (typechecking dager), are
arguments cast (type-loss danger), etc. Looks very hard to implement
though :-/ Andy, what do you think?

Ingo


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