linux-kernel - Re: [PATCH] arm64: vdso: Fix Makefile regression

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Message-ID: <20190731162309.6sqeylyoauv7seeb@willie-the-truck>
Date:   Wed, 31 Jul 2019 17:23:10 +0100
From:   Will Deacon <will@...nel.org>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, catalin.marinas@....com,
        arnd@...db.de, tglx@...utronix.de, salyzyn@...roid.com,
        pcc@...gle.com, 0x7f454c46@...il.com, linux@...musvillemoes.dk,
        sthotton@...vell.com, andre.przywara@....com, luto@...nel.org,
        Matteo Croce <mcroce@...hat.com>
Subject: Re: [PATCH] arm64: vdso: Fix Makefile regression

On Mon, Jul 29, 2019 at 01:54:21PM +0100, Vincenzo Frascino wrote:
> Using an old .config in combination with "make oldconfig" can cause
> an incorrect detection of the compat compiler:
> 
> $ grep CROSS_COMPILE_COMPAT .config
> CONFIG_CROSS_COMPILE_COMPAT_VDSO=""
> 
> $ make oldconfig && make
> arch/arm64/Makefile:58: gcc not found, check CROSS_COMPILE_COMPAT.
> Stop.
> 
> Accordingly to the section 7.2 of the GNU Make manual "Syntax of
> Conditionals", "When the value results from complex expansions of
> variables and functions, expansions you would consider empty may
> actually contain whitespace characters and thus are not seen as
> empty. However, you can use the strip function to avoid interpreting
> whitespace as a non-empty value."
> 
> Fix the issue adding strip to the CROSS_COMPILE_COMPAT string
> evaluation.
> 
> Cc: Will Deacon <will@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Reported-by: Matteo Croce <mcroce@...hat.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
> ---
>  arch/arm64/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index bb1f1dbb34e8..61de992bbea3 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -52,7 +52,7 @@ ifeq ($(CONFIG_GENERIC_COMPAT_VDSO), y)
>  
>    ifeq ($(CONFIG_CC_IS_CLANG), y)
>      $(warning CROSS_COMPILE_COMPAT is clang, the compat vDSO will not be built)
> -  else ifeq ($(CROSS_COMPILE_COMPAT),)
> +  else ifeq ($(strip $(CROSS_COMPILE_COMPAT)),)
>      $(warning CROSS_COMPILE_COMPAT not defined or empty, the compat vDSO will not be built)
>    else ifeq ($(shell which $(CROSS_COMPILE_COMPAT)gcc 2> /dev/null),)
>      $(error $(CROSS_COMPILE_COMPAT)gcc not found, check CROSS_COMPILE_COMPAT)
> -- 
> 2.22.0

Acked-by: Will Deacon <will@...nel.org>

Will