netdev - Re: [PATCH net-next] tools: ynl: change the comment about header guards

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Date: Fri, 16 Jun 2023 08:59:22 +0200
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Jakub Kicinski <kuba@...nel.org>, <davem@...emloft.net>
CC: <netdev@...r.kernel.org>, <edumazet@...gle.com>, <pabeni@...hat.com>
Subject: Re: [PATCH net-next] tools: ynl: change the comment about header
 guards

On 6/16/23 05:12, Jakub Kicinski wrote:
> Przemek suggests that I shouldn't accuse GCC of witchcraft,
> there is a simpler explanation for why we need manual define.
> 
> scripts/headers_install.sh modifies the guard.
> 
> This also solves the mystery of why I needed to include
> the header conditionally. I had the wrong guards for most
> cases but ethtool.
> 
> Suggested-by: Przemek Kitszel <przemyslaw.kitszel@...el.com>
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> ---
>   tools/net/ynl/Makefile.deps | 16 ++++++----------
>   1 file changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/tools/net/ynl/Makefile.deps b/tools/net/ynl/Makefile.deps
> index 524fc4bb586b..cbf4cdfc4fed 100644
> --- a/tools/net/ynl/Makefile.deps
> +++ b/tools/net/ynl/Makefile.deps
> @@ -9,20 +9,16 @@
>   
>   UAPI_PATH:=../../../../include/uapi/
>   
> -# If the header does not exist at all in the system path - let the
> -# compiler fall back to the kernel header via -Idirafter.
> -# GCC seems to ignore header guard if the header is different, so we need
> -# to specify the -D$(hdr_guard).
> +# scripts/headers_install.sh strips "_UAPI" from header guards so we
> +# need the explicit -D to avoid multiple definitions.
>   # And we need to define HASH indirectly because GNU Make 4.2 wants it escaped
>   # and Gnu Make 4.4 wants it without escaping.
>   
>   HASH := \#

HASH, including explanation around it, could also go away now

>   
> -get_hdr_inc=$(if $(shell echo "$(HASH)include <linux/$(2)>" | \
> -			 cpp >>/dev/null 2>/dev/null && echo yes),\
> -		-D$(1) -include $(UAPI_PATH)/linux/$(2))
> +get_hdr_inc=-D$(1) -include $(UAPI_PATH)/linux/$(2)
>   
> -CFLAGS_devlink:=$(call get_hdr_inc,_UAPI_LINUX_DEVLINK_H_,devlink.h)
> +CFLAGS_devlink:=$(call get_hdr_inc,_LINUX_DEVLINK_H_,devlink.h)
>   CFLAGS_ethtool:=$(call get_hdr_inc,_LINUX_ETHTOOL_NETLINK_H_,ethtool_netlink.h)
> -CFLAGS_handshake:=$(call get_hdr_inc,_UAPI_LINUX_HANDSHAKE_H,handshake.h)
> -CFLAGS_netdev:=$(call get_hdr_inc,_UAPI_LINUX_NETDEV_H,netdev.h)
> +CFLAGS_handshake:=$(call get_hdr_inc,_LINUX_HANDSHAKE_H,handshake.h)
> +CFLAGS_netdev:=$(call get_hdr_inc,_LINUX_NETDEV_H,netdev.h)

Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@...el.com>