linux-kernel - Re: [PATCH 3/4] tools lib feature: Do not redefine compiler configuration

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Date:   Mon, 6 Feb 2017 10:38:59 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     David Carrillo-Cisneros <davidcc@...gle.com>
Cc:     Mark Rutland <mark.rutland@....com>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Wang Nan <wangnan0@...wei.com>, He Kuang <hekuang@...wei.com>,
        Michal Marek <mmarek@...e.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Stephane Eranian <eranian@...gle.com>,
        Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH 3/4] tools lib feature: Do not redefine compiler
 configuration

Em Wed, Feb 01, 2017 at 10:38:03PM -0800, David Carrillo-Cisneros escreveu:
> Feature detection redefines CC, CCX and PKG_CONFIG, making the
> output of feature detection inconsistent with the actual features
> available during compilation when the above variables are used.
> 
> Fix it by using conditional assignment.

This one is tricky, the real meaning of that line got lost somewhere,
its original intent, in commit 8b6eb56a9570 ("tools/perf/build: Add
'autodep' functionality, generate feature test dependencies
automatically") was to just add that "-MD" to whatever definition CC
had, be it the default one or a value set by the user in the make
command line.

At some point someone added that CROSS_COMPILE there, which it should
have gotten from the default CC definition

It was here: a8a5cd8b472c ("perf: tools: Fix cross building")

    perf: tools: Fix cross building
    
    Currently the feature-checks Makefile does not inherit $(CC), and calls
    cc rather than $(CROSS_COMPILE)gcc. Thus the feature checks invoke the
    native toolchain rather than the cross toolchain, and can identify
    features as available when they are not. This can break the build

----------------------------------

Mark, do you recall why can't we make tools/perf/Makefile.perf pass the
definitions of CC, AR and PKG_CONFIG to tools/perf/config/Makefile (now
tools/build/feature/Makefile) so that the original intent (adding -MD to
whatever was in CC) can be kept?

Jiri?

- Arnaldo
 
> Signed-off-by: David Carrillo-Cisneros <davidcc@...gle.com>
> ---
>  tools/build/feature/Makefile | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile
> index 3dd2c600d250..d39e76f3a063 100644
> --- a/tools/build/feature/Makefile
> +++ b/tools/build/feature/Makefile
> @@ -52,9 +52,9 @@ FILES=                                          \
>  
>  FILES := $(addprefix $(OUTPUT),$(FILES))
>  
> -CC := $(CROSS_COMPILE)gcc -MD
> -CXX := $(CROSS_COMPILE)g++ -MD
> -PKG_CONFIG := $(CROSS_COMPILE)pkg-config
> +CC ?= $(CROSS_COMPILE)gcc -MD
> +CXX ?= $(CROSS_COMPILE)g++ -MD
> +PKG_CONFIG ?= $(CROSS_COMPILE)pkg-config
>  LLVM_CONFIG ?= llvm-config
>  
>  all: $(FILES)
> -- 
> 2.11.0.483.g087da7b7c-goog