linux-kernel - Re: [PATCH] btrfs: Use immediate assignment when referencing cc-option

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Message-ID: <8d9d9142-ae55-c40a-5546-e1c0384641fa@suse.com>
Date:   Wed, 17 Mar 2021 08:39:45 +0200
From:   Nikolay Borisov <nborisov@...e.com>
To:     Victor Erminpour <victor.erminpour@...cle.com>, clm@...com
Cc:     josef@...icpanda.com, dsterba@...e.com,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: Use immediate assignment when referencing
 cc-option



On 17.03.21 г. 0:46 ч., Victor Erminpour wrote:
> Calling cc-option will use KBUILD_CFLAGS, which when lazy setting
> subdir-ccflags-y produces the following build error:
> 
> scripts/Makefile.lib:10: *** Recursive variable `KBUILD_CFLAGS' \
> 	references itself (eventually).  Stop.
> 
> Use := assignment to subdir-ccflags-y when referencing cc-option.
> This causes make to also evaluate += immediately, cc-option
> calls are done right away and we don't end up with KBUILD_CFLAGS
> referencing itself.
> 
> Signed-off-by: Victor Erminpour <victor.erminpour@...cle.com>
> ---
>  fs/btrfs/Makefile | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile
> index b634c42115ea..3dba1336fa95 100644
> --- a/fs/btrfs/Makefile
> +++ b/fs/btrfs/Makefile
> @@ -7,10 +7,10 @@ subdir-ccflags-y += -Wmissing-format-attribute
>  subdir-ccflags-y += -Wmissing-prototypes
>  subdir-ccflags-y += -Wold-style-definition
>  subdir-ccflags-y += -Wmissing-include-dirs
> -subdir-ccflags-y += $(call cc-option, -Wunused-but-set-variable)
> -subdir-ccflags-y += $(call cc-option, -Wunused-const-variable)
> -subdir-ccflags-y += $(call cc-option, -Wpacked-not-aligned)
> -subdir-ccflags-y += $(call cc-option, -Wstringop-truncation)
> +subdir-ccflags-y := $(call cc-option, -Wunused-but-set-variable)
> +subdir-ccflags-y := $(call cc-option, -Wunused-const-variable)
> +subdir-ccflags-y := $(call cc-option, -Wpacked-not-aligned)
> +subdir-ccflags-y := $(call cc-option, -Wstringop-truncation)
>  # The following turn off the warnings enabled by -Wextra
>  subdir-ccflags-y += -Wno-missing-field-initializers
>  subdir-ccflags-y += -Wno-sign-compare
> 

Why does this patch change only some assignments and others are left as
they were?