linux-kernel - Re: [PATCH] kbuild: use more portable 'command -v' for cc-cross-prefix

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Message-ID: <CAK7LNASwTS+rfZuFFcR7cz2HaOZWMjxhZUToV=74g09J72=osg@mail.gmail.com>
Date:   Tue, 4 Jun 2019 12:44:25 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
        Vineet Gupta <vgupta@...opsys.com>,
        Alexey Brodkin <abrodkin@...opsys.com>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        linux-stable <stable@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kbuild: use more portable 'command -v' for cc-cross-prefix

On Mon, Jun 3, 2019 at 9:43 PM David Laight <David.Laight@...lab.com> wrote:
>
> From: Masahiro Yamada
> > Sent: 03 June 2019 12:45
> > On Mon, Jun 3, 2019 at 8:16 PM David Laight <David.Laight@...lab.com> wrote:
> > >
> > > From: Masahiro Yamada
> > > > Sent: 03 June 2019 11:49
> > > >
> > > > To print the pathname that will be used by shell in the current
> > > > environment, 'command -v' is a standardized way. [1]
> > > >
> > > > 'which' is also often used in scripting, but it is not portable.
> > >
> > > All uses of 'which' should be expunged.
> > > It is a bourne shell script that is trying to emulate a csh builtin.
> > > It is doomed to fail in corner cases.
> > > ISTR it has serious problems with shell functions and aliases.
> >
> > OK, I do not have time to check it treewide.
> > I expect somebody will contribute to it.
> >
> >
> >
> > BTW, I see yet another way to get the command path.
> >
> > 'type -path' is bash-specific.
>
> 'type' itself should be supported by all shells, but the output
> format (esp for errors) probably varies.
>
> > Maybe, we should do this too:
> >
> > diff --git a/scripts/mkuboot.sh b/scripts/mkuboot.sh
> > index 4b1fe09e9042..77829ee4268e 100755
> > --- a/scripts/mkuboot.sh
> > +++ b/scripts/mkuboot.sh
> > @@ -1,14 +1,14 @@
> > -#!/bin/bash
> > +#!/bin/sh
>
> /bin/sh might be 'dash' - which is just plain broken in so many ways.
> Try (IIRC) ${foo%${foo#bar}}
> It might even be the original SYSV /bin/sh which doesn't support $((expr))
> or ${foo#bar} - but that may break too much, but $SHELL might fix it.


We cannot use any tool
if you start to argue like
"Hey, I know ancient implementation that did not work as expected".

Nobody can cover all corner-cases.
That's why we have standard.

I think the reliable source is the
Open Group Specification.

The behavior of /bin/sh is defined here:
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_01

${parameter%[word]} and ${parameter#[word]} are defined,
so we can use them in /bin/sh scripts.


> dash probably has the rather obscure bug in stripping '\n' from $(...)
> output that I found and fixed in NetBSD's ash may years ago.
> Try: foo="$(jot -b "" 130)"
> All 130 '\n' should be deleted.
> Mostly it fails to delete all the '\n', but it can remove extra ones!
>
>         David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)



-- 
Best Regards
Masahiro Yamada