Messages in this thread | | | Subject | Re: [PATCH] powerpc/mm: fix always true/false warning in slice.c | From | Christophe Leroy <> | Date | Thu, 2 Aug 2018 09:30:31 +0000 |
| |
On 06/29/2018 02:55 AM, Michael Ellerman wrote: > Christophe Leroy <christophe.leroy@c-s.fr> writes: > >> This patch fixes the following warnings (obtained with make W=1). >> >> arch/powerpc/mm/slice.c: In function 'slice_range_to_mask': >> arch/powerpc/mm/slice.c:73:12: error: comparison is always true due to limited range of data type [-Werror=type-limits] >> if (start < SLICE_LOW_TOP) { > > Presumably only on 32-bit ?
Sure
> >> diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c >> index 9530c6db406a..17c57760e06c 100644 >> --- a/arch/powerpc/mm/slice.c >> +++ b/arch/powerpc/mm/slice.c >> @@ -79,7 +86,7 @@ static void slice_range_to_mask(unsigned long start, unsigned long len, >> - (1u << GET_LOW_SLICE_INDEX(start)); >> } >> >> - if ((start + len) > SLICE_LOW_TOP) { >> + if (!slice_addr_is_low(end)) { >> unsigned long start_index = GET_HIGH_SLICE_INDEX(start); >> unsigned long align_end = ALIGN(end, (1UL << SLICE_HIGH_SHIFT)); >> unsigned long count = GET_HIGH_SLICE_INDEX(align_end) - start_index; > > This worries me.
I'll change it in v2 to: if (SLICE_NUM_HIGH && !slice_addr_is_low(end)) {
> > By casting before the comparison in the helper you squash the compiler > warning, but the code is still broken if (start + len) overflows. > > Presumably that "never happens", but it just seems fishy. > > The other similar check in that file does: > > if (SLICE_NUM_HIGH && ((start + len) > SLICE_LOW_TOP)) { > > Where SLICE_NUM_HIGH == 0 on 32-bit. > > > Could we fix the less than comparisons with SLICE_LOW_TOP with something > similar, eg: > > if (!SLICE_NUM_HIGH || start < SLICE_LOW_TOP) { > > ie. limit them to the 64-bit code?
That's not enough to make GCC happy:
arch/powerpc/mm/slice.c: In function ‘slice_range_to_mask’: arch/powerpc/mm/slice.c:74:31: error: comparison is always true due to limited range of data type [-Werror=type-limits] if (!SLICE_NUM_HIGH || start < SLICE_LOW_TOP) {
Christophe
> > cheers >
| |