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Date: Sun, 18 Feb 2018 23:13:52 +0100
From: Sam Ravnborg <sam@...nborg.org>
To: Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc: linux-kbuild@...r.kernel.org,
Linus Torvalds <torvalds@...ux-foundation.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
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Ulf Magnusson <ulfalizer@...il.com>,
Michal Marek <michal.lkml@...kovi.net>,
Peter Oberparleiter <oberpar@...ux.vnet.ibm.com>,
kernel-hardening@...ts.openwall.com,
Jonathan Corbet <corbet@....net>, sparclinux@...r.kernel.org,
linux-sh@...r.kernel.org, x86@...nel.org,
Thomas Gleixner <tglx@...utronix.de>, Rich Felker <dalias@...c.org>,
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user-mode-linux-devel@...ts.sourceforge.net,
Yoshinori Sato <ysato@...rs.sourceforge.jp>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
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Ingo Molnar <mingo@...hat.com>,
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linux-kernel@...r.kernel.org, Richard Weinberger <richard@....at>,
Emese Revfy <re.emese@...il.com>
Subject: Re: [PATCH 00/23] kconfig: move compiler capability tests to Kconfig
Hi Masahiro.
On Sat, Feb 17, 2018 at 03:38:28AM +0900, Masahiro Yamada wrote:
> I brushed up the implementation in this version.
>
> In the previous RFC, CC_HAS_ was described by using 'option shell=',
> like this:
>
> config CC_HAS_STACKPROTECTOR
> bool
> option shell="$CC -Werror -fstack-protector -c -x c /dev/null"
>
> After I thought a bit more, the following syntax is more grammatical,
> and flexible.
>
> config CC_HAS_STACKPROTECTOR
> bool
> default $(shell $CC -Werror -fstack-protector -c -x c /dev/null)
Looks good - but maybe we should go one step further.
So we in the syntax explicit handles:
- shell commands
- other commands, defined as strings
- environment variables
- config variables
Each case is explicit - so the reader is not confused what is used when.
$(shell foo) - output of the shell command foo. Uses $SHELL as the shell.
May include optional paramters.
foo may be a config variable referenced using ${} or a config variable prefixed with $
Example:
config BUILD_DIR
string
default $(shell cd ${objtree}; pwd)
$(call bar) - output of the bar command that may take optional parameters.
bar may be a text string, a config variable or an environment variable
The definition of bar may reference the parameters using $(1), $(2)
In this context a config variable needs to be prefixed with $
Example:
config reverse
string
default $(2) $(1)
config NEW_ORDER
string
$(call $reverse, A, B) # Will assign REVERSE the value "B A"
Example2:
config CC_OPTION
string
default $(shell ${srctree}/scripts/cc-option ${CC} $(1) $(2))
config CC_OPTIMIZE
string
$(call $CC_OPTION, -Oz, -Os)
${FOO} - environment variable
The above is inspired by how make implement similar functionality.
I'm not happy that we in one context can reference CONFIG variables
directly, but inside the $(call ...) and $(shell ...) needs the $ prefix.
But I could not come up with something un-ambigious where this could be avoided.
The above proposal include the functionality of the macro stuff proposed in this patch-set.
But with a simpler syntax and we keep all the other kconfig logic (depends on etc) - so
users will not be limited in their creativity.
> Current limitations:
>
> Dependency on outside scripts.
> Inter-option dependency:
> Functions are evaluated statically:
Same limitations exists with the syntax suggested above.
Sam
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