On Wed, May 02, 2018 at 10:19:30AM -0400, Steven Rostedt wrote:
> On Wed, 2 May 2018 21:45:00 +0800
> changbin.du@xxxxxxxxx wrote:
>
> > From: Changbin Du <changbin.du@xxxxxxxxx>
> >
> > With '-Og' optimization level, GCC would not optimize a count for a loop
> > as a constant value. But BUILD_BUG_ON() only accept compile-time constant
> > values.
> >
> > arch/arm/mm/mmu.o: In function `fix_to_virt':
> > /home/changbin/work/linux/./include/asm-generic/fixmap.h:31: undefined reference to `__compiletime_assert_31'
> > Makefile:1051: recipe for target 'vmlinux' failed
> > make: *** [vmlinux] Error 1
> >
> > Signed-off-by: Changbin Du <changbin.du@xxxxxxxxx>
> > ---
> > include/asm-generic/fixmap.h | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/asm-generic/fixmap.h b/include/asm-generic/fixmap.h
> > index 827e4d3..a6576d4 100644
> > --- a/include/asm-generic/fixmap.h
> > +++ b/include/asm-generic/fixmap.h
> > @@ -28,7 +28,8 @@
> > */
> > static __always_inline unsigned long fix_to_virt(const unsigned int idx)
> > {
> > - BUILD_BUG_ON(idx >= __end_of_fixed_addresses);
> > + BUILD_BUG_ON(__builtin_constant_p(idx) &&
> > + idx >= __end_of_fixed_addresses);
>
> Hmm, this changes the check slightly. Perhaps we should only do this
> when your config is active:
>
> {
> BUILD_BUG_ON(
> /* CONFIG_DEBUG_OPTIMIZE may cause idx not to be constant */
> #ifdef CONFIG_DEBUG_OPTIMIZE
> __builtin_constant_p(idx) &&
> #endif
> idx >= __end_of_fixed_addresses);
>
> }
I think fix_to_virt() is designed for constant idx only. So I think we should
fix it at the caller side by replacing it with __fix_to_virt().
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -1599,7 +1599,7 @@ static void __init early_fixmap_shutdown(void)
pte_t *pte;
struct map_desc map;
- map.virtual = fix_to_virt(i);
+ map.virtual = __fix_to_virt(i);
pte = pte_offset_early_fixmap(pmd_off_k(map.virtual), map.virtual);
>
> -- Steve
>
> > return __fix_to_virt(idx);
> > }
> >
>
--
Thanks,
Changbin Du
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