Le ven. 17 mai 2024, 21:26, Gao Xiang <hsiang...@linux.alibaba.com> a écrit :
> Hi Vladimir, > > On 2024/5/18 00:38, Vladimir 'phcoder' Serbinenko wrote: > > I think that given that align is a non zero const we can trust it. > > From the EROFS specific cases, they are always non-zero values, > So I agree with you on this.. > > Yet Daniel said ".. Be careful with underflows too." in > https://lore.kernel.org/r/zkcv7g7mjbg8s...@tomti.i.net-space.pl > although I'm not quite sure but I guess like this. > > Also as a generic helper, I think `align` could be zero if it's > a variable.. > It's rare for align to be a variable and then additional checks are needed that align is a power of 2. And power of 2 is never zero. This check is better done on the caller side. You just need a comment specify that it's caller responsibility to check it. > > Anyway, either way works for EROFS. I just try my best to do > what I could do for this first series for upstreaming and we > could move forward to the next step.. > > Thanks, > Gao Xiang > > > > > Le ven. 17 mai 2024, 15:56, Gao Xiang <hsiang...@linux.alibaba.com > <mailto:hsiang...@linux.alibaba.com>> a écrit : > > > > The following EROFS patch will use this helper to handle overflow > > ALIGN_UP() cases. > > > > Signed-off-by: Gao Xiang <hsiang...@linux.alibaba.com <mailto: > hsiang...@linux.alibaba.com>> > > --- > > include/grub/safemath.h | 16 ++++++++++++++++ > > 1 file changed, 16 insertions(+) > > > > diff --git a/include/grub/safemath.h b/include/grub/safemath.h > > index fbd9b5925..baaea0ef4 100644 > > --- a/include/grub/safemath.h > > +++ b/include/grub/safemath.h > > @@ -32,6 +32,22 @@ > > > > #define grub_cast(a, res) grub_add ((a), 0, (res)) > > > > +#define ALIGN_UP_OVF(v, align, res) \ > > +({ \ > > + bool __failed; \ > > + typeof(v) a; \ > > + \ > > + __failed = grub_sub ((typeof(v))(align), 1, &a); \ > > + if (__failed == false) \ > > + { \ > > + __failed = grub_add (v, a, res); \ > > + if (__failed == false) \ > > + { \ > > + *(res) &= ~a; \ > > + } \ > > + } \ > > +__failed;}) > > + > > #else > > #error gcc 5.1 or newer or clang 8.0 or newer is required > > #endif > > -- > > 2.39.3 > > >
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