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? 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
