Re: [PATCH 02/23] lib: move 64-bit div/mod compiler helpers

From: Julien Grall <julien@xen.org>
To: Jan Beulich <jbeulich@suse.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: "Andrew Cooper" <andrew.cooper3@citrix.com>,
	"George Dunlap" <george.dunlap@citrix.com>,
	"Ian Jackson" <iwj@xenproject.org>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	"Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [PATCH 02/23] lib: move 64-bit div/mod compiler helpers
Date: Thu, 1 Apr 2021 15:56:53 +0100	[thread overview]
Message-ID: <008a8b14-8f58-2127-9e97-87c696e07b5e@xen.org> (raw)
In-Reply-To: <0fec827f-bb0b-4ea1-7757-9c27e9138be7@suse.com>

Hi Jan,

On 01/04/2021 11:19, Jan Beulich wrote:
> These were built for 32-bit architectures only (the same code could,
> with some tweaking, sensibly be used to provide TI-mode helpers on
> 64-bit arch-es) - retain this property, while still avoiding to have
> a CU without any contents at all. For this, Arm's CONFIG_64BIT gets
> generalized.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> ---
>   xen/arch/Kconfig                   |  2 ++
>   xen/arch/arm/Kconfig               | 12 +++---------
>   xen/arch/x86/Kconfig               |  1 +
>   xen/common/Makefile                |  1 -
>   xen/lib/Makefile                   |  4 ++++
>   xen/{common/lib.c => lib/divmod.c} |  2 --
>   6 files changed, 10 insertions(+), 12 deletions(-)
>   rename xen/{common/lib.c => lib/divmod.c} (99%)
> 
> diff --git a/xen/arch/Kconfig b/xen/arch/Kconfig
> index d144d4c8d3ee..f16eb0df43af 100644
> --- a/xen/arch/Kconfig
> +++ b/xen/arch/Kconfig
> @@ -1,3 +1,5 @@
> +config 64BIT
> +	bool
>   
>   config NR_CPUS
>   	int "Maximum number of CPUs"
> diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
> index 330bbf6232d4..ecfa6822e4d3 100644
> --- a/xen/arch/arm/Kconfig
> +++ b/xen/arch/arm/Kconfig
> @@ -1,17 +1,11 @@
> -config 64BIT
> -	bool
> -	default "$(ARCH)" != "arm32"
> -	help
> -	  Say yes to build a 64-bit Xen
> -	  Say no to build a 32-bit Xen
> -
>   config ARM_32
>   	def_bool y
> -	depends on !64BIT
> +	depends on "$(ARCH)" = "arm32"
>   
>   config ARM_64
>   	def_bool y
> -	depends on 64BIT
> +	depends on !ARM_32
> +	select 64BIT
>   	select HAS_FAST_MULTIPLY
>   
>   config ARM
> diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
> index f79e6634db3f..4d6911ffa467 100644
> --- a/xen/arch/x86/Kconfig
> +++ b/xen/arch/x86/Kconfig
> @@ -1,5 +1,6 @@
>   config X86_64
>   	def_bool y
> +	select 64BIT
>   
>   config X86
>   	def_bool y
> diff --git a/xen/common/Makefile b/xen/common/Makefile
> index 71c1d466bd8f..e2a7e62d14bf 100644
> --- a/xen/common/Makefile
> +++ b/xen/common/Makefile
> @@ -21,7 +21,6 @@ obj-y += kernel.o
>   obj-y += keyhandler.o
>   obj-$(CONFIG_KEXEC) += kexec.o
>   obj-$(CONFIG_KEXEC) += kimage.o
> -obj-y += lib.o
>   obj-$(CONFIG_LIVEPATCH) += livepatch.o livepatch_elf.o
>   obj-$(CONFIG_MEM_ACCESS) += mem_access.o
>   obj-y += memory.o
> diff --git a/xen/lib/Makefile b/xen/lib/Makefile
> index 0b274583ef0b..a5dc1442a422 100644
> --- a/xen/lib/Makefile
> +++ b/xen/lib/Makefile
> @@ -10,3 +10,7 @@ lib-y += rbtree.o
>   lib-y += sort.o
>   lib-$(CONFIG_X86) += xxhash32.o
>   lib-$(CONFIG_X86) += xxhash64.o
> +
> +lib32-y := divmod.o
> +lib32-$(CONFIG_64BIT) :=
> +lib-y += $(lib32-y)
> diff --git a/xen/common/lib.c b/xen/lib/divmod.c
> similarity index 99%
> rename from xen/common/lib.c
> rename to xen/lib/divmod.c
> index 5b8f49153dad..0be6ccc70096 100644
> --- a/xen/common/lib.c
> +++ b/xen/lib/divmod.c
> @@ -40,7 +40,6 @@
>    * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
>    * SUCH DAMAGE.
>    */
> -#if BITS_PER_LONG == 32

In theory BITS_PER_LONG == 32 is not quite the same as 32-bit arch. Can 
you clarify whether this code is necessary on 64-bit arch where long is 
only 32-bit.

Cheers?

-- 
Julien Grall