linux-kernel - Re: [PATCH] kbuild: resolve symlinks for O= properly

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Message-ID: <ZXwcfSsuhzJYNAQh@buildd.core.avm.de>
Date: Fri, 15 Dec 2023 10:29:30 +0100
From: Nicolas Schier <n.schier@....de>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: linux-kbuild@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kbuild: resolve symlinks for O= properly

On Thu, Dec 14, 2023 at 11:03:05PM +0900, Masahiro Yamada wrote:
> Currently, Kbuild follows the logical chain of directories for the O=
> option, just like 'cd' (or 'realpath --logical') does.
> 
> Example:
> 
>     $ mkdir -p /tmp/a /tmp/x/y
>     $ ln -s /tmp/x/y /tmp/a/b
>     $ realpath /tmp/a/b/..
>     /tmp/x
>     $ realpath --logical /tmp/a/b/..
>     /tmp/a
>     $ make O=/tmp/a/b/.. defconfig
>     make[1]: Entering directory '/tmp/a'
>       [snip]
>     make[1]: Leaving directory '/tmp/a'
> 
> 'make O=/tmp/a/b/.. defconfig' creates the kernel configuration in
> /tmp/a instead of /tmp/x despite the directory path /tmp/a/b/..
> resolves to the physical directory path /tmp/x.
> 
> This is because Kbuild internally uses the 'cd ... && pwd' for the
> path resolution, but this behavior is not predictable for users.
> Additionally, it is not consistent with how the Kbuild handles the
> M= option or GNU Make works with 'make -C /tmp/a/b/..'.
> 
> Using the physical directory structure for the O= option seems more
> reasonable.
> 
> The comment says "expand a shell special character '~'", but it has
> already been expanded to the home directory in the command line.

I minor change in behaviour is that 'make O="~/..."' (=quoted '~) will
not work any more.  But I think this actually the way it should be.
Thanks!

Reviewed-by: Nicolas Schier <n.schier@....de>


> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
> 
>  Makefile | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 24fac1889997..a05f0f7c99e0 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -190,14 +190,11 @@ ifeq ("$(origin O)", "command line")
>  endif
>  
>  ifneq ($(KBUILD_OUTPUT),)
> -# Make's built-in functions such as $(abspath ...), $(realpath ...) cannot
> -# expand a shell special character '~'. We use a somewhat tedious way here.
> -abs_objtree := $(shell mkdir -p $(KBUILD_OUTPUT) && cd $(KBUILD_OUTPUT) && pwd)
> -$(if $(abs_objtree),, \
> -     $(error failed to create output directory "$(KBUILD_OUTPUT)"))
> -
> +# $(realpath ...) gets empty if the path does not exist. Run 'mkdir -p' first.
> +$(shell mkdir -p $(KBUILD_OUTPUT))
>  # $(realpath ...) resolves symlinks
> -abs_objtree := $(realpath $(abs_objtree))
> +abs_objtree := $(realpath $(KBUILD_OUTPUT))
> +$(if $(abs_objtree),,$(error failed to create output directory "$(KBUILD_OUTPUT)"))
>  endif # ifneq ($(KBUILD_OUTPUT),)
>  
>  ifneq ($(words $(subst :, ,$(abs_srctree))), 1)
> -- 
> 2.40.1
> 

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