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Date:   Wed, 17 Mar 2021 18:05:31 +0100
From:   David Sterba <dsterba@suse.cz>
To:     Victor Erminpour <victor.erminpour@oracle.com>
Cc:     clm@fb.com, josef@toxicpanda.com, dsterba@suse.com,
        linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] btrfs: Use immediate assignment when referencing
 cc-option
Message-ID: <20210317170531.GU7604@twin.jikos.cz>
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On Wed, Mar 17, 2021 at 09:08:48AM -0700, 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 single := assignment for subdir-ccflags-y. The 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@oracle.com>
> ---
>  fs/btrfs/Makefile | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile
> index b634c42115ea..583ca2028e08 100644
> --- a/fs/btrfs/Makefile
> +++ b/fs/btrfs/Makefile
> @@ -1,16 +1,16 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
>  # Subset of W=1 warnings
> +subdir-ccflags-y := $(call cc-option, -Wunused-but-set-variable) \
> +	$(call cc-option, -Wunused-const-variable) \
> +	$(call cc-option, -Wpacked-not-aligned) \
> +	$(call cc-option, -Wstringop-truncation)

That's still overwriting the value unconditionally, the idea was a
separate variable

https://lore.kernel.org/linux-btrfs/20210317104313.17028-1-dsterba@suse.com