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Date:   Sat, 22 Feb 2020 09:01:13 +0000
From:   Russell King - ARM Linux admin <linux@armlinux.org.uk>
To:     Masahiro Yamada <masahiroy@kernel.org>
Cc:     "Alex Xu (Hello71)" <alex_y_xu@yahoo.ca>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] kbuild: move -pipe to global KBUILD_CFLAGS
Message-ID: <20200222090113.GM25745@shell.armlinux.org.uk>
References: <20200222003820.220854-1-alex_y_xu.ref@yahoo.ca>
 <20200222003820.220854-1-alex_y_xu@yahoo.ca>
 <CAK7LNARNEu2gVBVDpRtbha_n=RWWfcQu57LtO=CbLBXLU9Ds-g@mail.gmail.com>
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On Sat, Feb 22, 2020 at 11:07:14AM +0900, Masahiro Yamada wrote:
> On Sat, Feb 22, 2020 at 9:40 AM Alex Xu (Hello71) <alex_y_xu@yahoo.ca> wrote:
> >
> > -pipe reduces unnecessary disk wear for systems where /tmp is not a
> > tmpfs, slightly increases compilation speed, and avoids leaving behind
> > files when gcc crashes.
> >
> > According to the gcc manual, "this fails to work on some systems where
> > the assembler is unable to read from a pipe; but the GNU assembler has
> > no trouble". We already require GNU ld on all platforms, so this is not
> > an additional dependency. LLVM as also supports pipes.
> >
> > -pipe has always been used for most architectures, this change
> > standardizes it globally. Most notably, arm, arm64, riscv, and x86 are
> > affected.
> >
> > Signed-off-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
> 
> <snip>
> 
> > diff --git a/arch/arc/Makefile b/arch/arc/Makefile
> > index 20e9ab6cc521..b6a2f553771c 100644
> > --- a/arch/arc/Makefile
> > +++ b/arch/arc/Makefile
> > @@ -9,7 +9,7 @@ ifeq ($(CROSS_COMPILE),)
> >  CROSS_COMPILE := $(call cc-cross-prefix, arc-linux- arceb-linux-)
> >  endif
> >
> > -cflags-y       += -fno-common -pipe -fno-builtin -mmedium-calls -D__linux__
> > +cflags-y       += -fno-common -fno-builtin -mmedium-calls -D__linux__
> >  cflags-$(CONFIG_ISA_ARCOMPACT) += -mA7
> >  cflags-$(CONFIG_ISA_ARCV2)     += -mcpu=hs38
> >
> > diff --git a/arch/arm/Makefile b/arch/arm/Makefile
> > index db857d07114f..7711467e0797 100644
> > --- a/arch/arm/Makefile
> > +++ b/arch/arm/Makefile
> > @@ -21,7 +21,6 @@ KBUILD_LDS_MODULE     += $(srctree)/arch/arm/kernel/module.lds
> >  endif
> >
> >  GZFLAGS                :=-9
> > -#KBUILD_CFLAGS +=-pipe
> 
> 
> This was commented out by a very old commit,
> which is available in the historical git tree.
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/commit/?id=ce20ed858a20f6f04de475cae79e40d3697f4776
> 
> But, I could not parse the reason from the commit message.
> Russell, do you remember why?

-pipe may reduce the disk load but increases the CPU load, so it's an
option that's up to the build environment.  One may wish to pass a
lower parralellism when using -pipe to make to mitigate that, but both
options are up to the build environment to decide upon.

If we unconditionally add -pipe, then we take away choice.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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