Balbir Singh <bsinghar...@gmail.com> writes: > On Sat, Feb 16, 2019 at 08:22:12AM -0600, Segher Boessenkool wrote: >> Hi all, >> >> On Sat, Feb 16, 2019 at 09:55:11PM +1100, Balbir Singh wrote: >> > On Thu, Feb 14, 2019 at 05:23:39PM +1100, Michael Ellerman wrote: >> > > In v4.20 we changed our pgd/pud_present() to check for _PAGE_PRESENT >> > > rather than just checking that the value is non-zero, e.g.: >> > > >> > > static inline int pgd_present(pgd_t pgd) >> > > { >> > > - return !pgd_none(pgd); >> > > + return (pgd_raw(pgd) & cpu_to_be64(_PAGE_PRESENT)); >> > > } >> > > >> > > Unfortunately this is broken on big endian, as the result of the >> > > bitwise && is truncated to int, which is always zero because >> >> (Bitwise "&" of course). >> >> > Not sure why that should happen, why is the result an int? What >> > causes the casting of pgd_t & be64 to be truncated to an int. >> >> Yes, it's not obvious as written... It's simply that the return type of >> pgd_present is int. So it is truncated _after_ the bitwise and. >> > > Thanks, I am surprised the compiler does not complain about the truncation > of bits. I wonder if we are missing -Wconversion
Good luck with that :) What I should start doing is building with it enabled and then comparing the output before and after commits to make sure we're not introducing new cases. cheers