On Mon, Sep 13, 2021 at 9:53 PM 'Nick Desaulniers' via Clang Built Linux <clang-built-linux@xxxxxxxxxxxxxxxx> wrote: > > On Mon, Sep 13, 2021 at 11:39 AM Nick Desaulniers > <ndesaulniers@xxxxxxxxxx> wrote: > > > > On Mon, Sep 13, 2021 at 10:58 AM Greg Kroah-Hartman > > <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > On Mon, Sep 13, 2021 at 09:52:33PM +0530, Naresh Kamboju wrote: > > > > [PATCH 00/10] raise minimum GCC version to 5.1 > > > > https://lore.kernel.org/lkml/20210910234047.1019925-1-ndesaulniers@xxxxxxxxxx/ > > > > > > Has anyone submitted a fix for this upstream yet? I can't seem to find > > > one :( > > > > That lore link has a series to address this, though that's maybe > > something we don't want to backport to stable. > > > > I thought about this all weekend; I think I might be able to work > > around the one concern I had with my other approach, using > > __builtin_choose_expr(). > > > > There's an issue with my alternative approach > > (https://gist.github.com/nickdesaulniers/2479818f4983bbf2d688cebbab435863) > > with declaring the local variable z in div_64() since either operand > > could be 64b, which result in an unwanted truncation if the dividend > > is 32b (or less, and divisor is 64b). I think (what I realized this > > weekend) is that we might be able to replace the `if` with > > `__builtin_choose_expr`, then have that whole expression be the final > > statement and thus the "return value" of the statement expression. > > Christ...that...works? Though, did Linus just merge my patches for gcc 5.1? > "Merge branch 'gcc-min-version-5.1' (make gcc-5.1 the minimum version)" - Sedat - https://git.kernel.org/linus/316346243be6df12799c0b64b788e06bad97c30b > Anyways, I'll send something like this for stable: > --- > > diff --git a/include/linux/math64.h b/include/linux/math64.h > index 2928f03d6d46..e9ab8c25f8d3 100644 > --- a/include/linux/math64.h > +++ b/include/linux/math64.h > @@ -11,6 +11,9 @@ > > #define div64_long(x, y) div64_s64((x), (y)) > #define div64_ul(x, y) div64_u64((x), (y)) > +#ifndef is_signed_type > +#define is_signed_type(type) (((type)(-1)) < (type)1) > +#endif > > /** > * div_u64_rem - unsigned 64bit divide with 32bit divisor with remainder > @@ -112,6 +115,15 @@ extern s64 div64_s64(s64 dividend, s64 divisor); > > #endif /* BITS_PER_LONG */ > > +#define div64_x64(dividend, divisor) ({ \ > + BUILD_BUG_ON_MSG(sizeof(dividend) < sizeof(u64),\ > + "prefer div_x64"); \ > + __builtin_choose_expr( \ > + is_signed_type(typeof(dividend)), \ > + div64_s64(dividend, divisor), \ > + div64_u64(dividend, divisor)); \ > +}) > + > /** > * div_u64 - unsigned 64bit divide with 32bit divisor > * @dividend: unsigned 64bit dividend > @@ -142,6 +154,28 @@ static inline s64 div_s64(s64 dividend, s32 divisor) > } > #endif > > +#define div_x64(dividend, divisor) ({ \ > + BUILD_BUG_ON_MSG(sizeof(dividend) > sizeof(u32),\ > + "prefer div64_x64"); \ > + __builtin_choose_expr( \ > + is_signed_type(typeof(dividend)), \ > + div_s64(dividend, divisor), \ > + div_u64(dividend, divisor)); \ > +}) > + > +// TODO: what if divisor is 128b? > +#define div_64(dividend, divisor) ({ > \ > + __builtin_choose_expr( > \ > + __builtin_types_compatible_p(typeof(dividend), s64) || > \ > + __builtin_types_compatible_p(typeof(dividend), u64), > \ > + __builtin_choose_expr( > \ > + __builtin_types_compatible_p(typeof(divisor), > s64) || \ > + __builtin_types_compatible_p(typeof(divisor), > u64), \ > + div64_x64(dividend, divisor), > \ > + div_x64(dividend, divisor)), > \ > + dividend / divisor); > \ > +}) > + > u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder); > > #ifndef mul_u32_u32 > --- > -- > Thanks, > ~Nick Desaulniers > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@xxxxxxxxxxxxxxxx. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/CAKwvOdmCS5Q7AzUL5nziYVU7RrtRjoE9JjOXfVBWagO1Bzbsew%40mail.gmail.com.
