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

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Message-ID: <CAK7LNASQ121fDts9cCx744XANqQRX2xrbDLVsiHC2ht8X4Fwkw@mail.gmail.com>
Date: Sat, 16 Dec 2023 00:58:58 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Masahiro Yamada <masahiroy@...nel.org>, 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 Fri, Dec 15, 2023 at 6:29 PM Nicolas Schier <n.schier@....de> wrote:
>
> 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!


A good catch. This bug should be fixed by quoting $(KBUILD_OUTPUT).


-$(shell mkdir -p $(KBUILD_OUTPUT))
+$(shell mkdir -p "$(KBUILD_OUTPUT)")



When ~ is quoted, it loses a special meaning.


masahiro@zoe:~$ echo ~
/home/masahiro
masahiro@zoe:~$ echo "~"
~



So, the right behaviour of 'make O="~/foo"' is
to create "~/foo" under the current directory.


If you try to test it, please be careful to
not delete your home directory.

(I did "rm -r ./~" just in case)











> 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
> >



-- 
Best Regards
Masahiro Yamada