Re: [PATCH kvmtool] remove wordsize.h inclusion (for musl compatibility)

[Alexandru Elisei <alexandru.elisei@arm.com>]

Hi Andre,

On Thu, Aug 01, 2024 at 12:10:54PM +0100, Andre Przywara wrote:
> The wordsize.h header file and the __WORDSIZE definition do not seem
> to be universal, the musl libc for instance has the definition in a
> different header file. This breaks compilation of kvmtool against musl.
> 
> The two leading underscores suggest a compiler-internal symbol anyway, so
> let's just remove that particular macro usage entirely, and replace it
> with the number we really want: the size of a "long" type.
> 
> Reported-by: J. Neuschäfer <j.neuschaefer@gmx.net>
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
> Hi,
> 
> can someone test this on a proper/pure musl installation? I tested this
> with Ubuntu's musl-gcc wrapper, but this didn't show the problem before,
> so I guess there are subtle differences.
> 
> Cheers,
> Andre
> 
>  include/linux/bitops.h | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
> index ae33922f5..ee8fd5609 100644
> --- a/include/linux/bitops.h
> +++ b/include/linux/bitops.h
> @@ -1,15 +1,13 @@
>  #ifndef _KVM_LINUX_BITOPS_H_
>  #define _KVM_LINUX_BITOPS_H_
>  
> -#include <bits/wordsize.h>
> -
>  #include <linux/kernel.h>
>  #include <linux/compiler.h>
>  #include <asm/hweight.h>
>  
> -#define BITS_PER_LONG __WORDSIZE
>  #define BITS_PER_BYTE           8
> -#define BITS_TO_LONGS(nr)       DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))
> +#define BITS_PER_LONG           (BITS_PER_BYTE * sizeof(long))
> +#define BITS_TO_LONGS(nr)       DIV_ROUND_UP(nr, BITS_PER_LONG)

This makes perfect sense to me. I would just like to point out that the code
already used this definition for the number of bits in a long, in the
BITS_TO_LONGS() macro, where it used BITS_PER_BYTE * sizeof(long) instead of
BITS_PER_LONG.

Also tested this by cross-compiling for arm and arm64 on an x86 host, and
compiling natively for arm64.

Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>

Thanks,
Alex

>  
>  #define BIT_WORD(nr)		((nr) / BITS_PER_LONG)
>  
> -- 
> 2.25.1
>