Re: [PATCH] kbuild: use more portable 'command -v' for cc-cross-prefix
On Tue, Jun 4, 2019 at 6:01 PM David Laight wrote:
>
> From: Masahiro Yamada
> > Sent: 04 June 2019 04:31
> ...
> > > > > You could use:
> > > > > $(shell sh -c "command -v $(c)gcc")
> > > > > or maybe:
> > > > > $(shell command$${x:+} -v $(c)gcc)
> > > >
> > > >
> > > > How about this?
> > > >
> > > > $(shell : ~; command -v $(c)gcc)
> > >
> > > Overcomplicated
> > >
> > > I've not looked at the list of 'special characters' in make,
> > > but I suspect any variable expansion is enough.
> > > Since ${x:+} always expands to the empty string (whether or
> > > not 'x' is defined) it can't have any unfortunate side effects.
> >
> >
> > Probably, my eyes are used to Makefile.
> > ":" is a no-op command, and it is used everywhere in kernel Makefiles
> > in the form of "@:'
> >
> > It depends on people which solution seems simpler.
> > So, this argument tends to end up with bikesheding.
>
> I am fully aware of ':', it is a shell builtin that always return success.
> Usually used when you want the side-effects of substitutions without
> executing anything (eg : ${foo:=bar} ), to change the result of a
> sequence of shell commands or as a dummy (eg while :; do :; done; )
> Very annoyingly bash parses !: as something other than 'not true'.
>
> $(shell command$${x:+} -v $(c)gcc) will be marginally faster
> because it is less parsing.
>
I will use this:
$(shell command -v $(c)gcc 2>/dev/null)
Make does not handle redirection by itself.
'2>/dev/null' is easy to understand,
and might be useful as extra safety.
--
Best Regards
Masahiro Yamada
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RE: [PATCH] kbuild: use more portable 'command -v' for cc-cross-prefix
From: Masahiro Yamada
> Sent: 04 June 2019 04:31
...
> > > > You could use:
> > > > $(shell sh -c "command -v $(c)gcc")
> > > > or maybe:
> > > > $(shell command$${x:+} -v $(c)gcc)
> > >
> > >
> > > How about this?
> > >
> > > $(shell : ~; command -v $(c)gcc)
> >
> > Overcomplicated
> >
> > I've not looked at the list of 'special characters' in make,
> > but I suspect any variable expansion is enough.
> > Since ${x:+} always expands to the empty string (whether or
> > not 'x' is defined) it can't have any unfortunate side effects.
>
>
> Probably, my eyes are used to Makefile.
> ":" is a no-op command, and it is used everywhere in kernel Makefiles
> in the form of "@:'
>
> It depends on people which solution seems simpler.
> So, this argument tends to end up with bikesheding.
I am fully aware of ':', it is a shell builtin that always return success.
Usually used when you want the side-effects of substitutions without
executing anything (eg : ${foo:=bar} ), to change the result of a
sequence of shell commands or as a dummy (eg while :; do :; done; )
Very annoyingly bash parses !: as something other than 'not true'.
$(shell command$${x:+} -v $(c)gcc) will be marginally faster
because it is less parsing.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT,
UK
Registration No: 1397386 (Wales)
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Re: [PATCH] kbuild: use more portable 'command -v' for cc-cross-prefix
On Mon, Jun 3, 2019 at 9:43 PM David Laight wrote:
>
> From: Masahiro Yamada
> > Sent: 03 June 2019 12:45
> > On Mon, Jun 3, 2019 at 8:16 PM David Laight 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
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Re: [PATCH] kbuild: use more portable 'command -v' for cc-cross-prefix
On Mon, Jun 3, 2019 at 10:09 PM David Laight wrote:
>
> From: Masahiro Yamada
> > Sent: 03 June 2019 12:38
> > Hi David,
> >
> > On Mon, Jun 3, 2019 at 8:14 PM David Laight 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.
> > > >
> > > > When I worked on commit bd55f96fa9fc ("kbuild: refactor cc-cross-prefix
> > > > implementation"), I was eager to use 'command -v' but it did not work.
> > > > (The reason is explained below.)
> > > >
> > > > I kept 'which' as before but got rid of '> /dev/null 2>&1' as I
> > > > thought it was no longer needed. Sorry, I was wrong.
> > > >
> > > > It works well on my Ubuntu machine, but Alexey Brodkin reports annoying
> > > > warnings from the 'which' on CentOS 7 when the given command is not
> > > > found in the PATH environment.
> > > >
> > > > $ which foo
> > > > which: no foo in
> > > > (/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin)
> > > >
> > > > Given that behavior of 'which' is different on environment, I want
> > > > to try 'command -v' again.
> > > >
> > > > The specification [1] clearly describes the behavior of 'command -v'
> > > > when the given command is not found:
> > > >
> > > > Otherwise, no output shall be written and the exit status shall
> > > > reflect
> > > > that the name was not found.
> > > >
> > > > However, we need a little magic to use 'command -v' from Make.
> > > >
> > > > $(shell ...) passes the argument to a subshell for execution, and
> > > > returns the standard output of the command.
> > > >
> > > > Here is a trick. GNU Make may optimize this by executing the command
> > > > directly instead of forking a subshell, if no shell special characters
> > > > are found in the command line and omitting the subshell will not
> > > > change the behavior.
> > > >
> > > > In this case, no shell special character is used. So, Make will try
> > > > to run the command directly. However, 'command' is a shell-builtin
> > > > command. In fact, Make has a table of shell-builtin commands because
> > > > it must spawn a subshell to execute them.
> > > >
> > > > Until recently, 'command' was missing in the table.
> > > >
> > > > This issue was fixed by the following commit:
> > > >
> > > > | commit 1af314465e5dfe3e8baa839a32a72e83c04f26ef
> > > > | Author: Paul Smith
> > > > | Date: Sun Nov 12 18:10:28 2017 -0500
> > > > |
> > > > | * job.c: Add "command" as a known shell built-in.
> > > > |
> > > > | This is not a POSIX shell built-in but it's common in UNIX shells.
> > > > | Reported by Nick Bowler .
> > > >
> > > > This is not included in any released versions of Make yet.
> > > > (But, some distributions may have back-ported the fix-up.)
> > > >
> > > > To trick Make and let it fork the subshell, I added a shell special
> > > > character '~'. We may be able to get rid of this workaround someday,
> > > > but it is very far into the future.
> > > >
> > > > [1]
> > > > http://pubs.opengroup.org/onlinepubs/9699919799/utilities/command.html
> > > >
> > > > Fixes: bd55f96fa9fc ("kbuild: refactor cc-cross-prefix implementation")
> > > > Cc: linux-stable # 5.1
> > > > Reported-by: Alexey Brodkin
> > > > Signed-off-by: Masahiro Yamada
> > > > ---
> > > >
> > > > scripts/Kbuild.include | 5 -
> > > > 1 file changed, 4 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> > > > index 85d758233483..5a32ca80c3f6 100644
> > > > --- a/scripts/Kbuild.include
> > > > +++ b/scripts/Kbuild.include
> > > > @@ -74,8 +74,11 @@ endef
> > > > # Usage: CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu-
> > > > m68k-linux-)
> > > > # Return first where a gcc is found in PATH.
> > > > # If no gcc found in PATH with listed prefixes return nothing
> > > > +#
> > > > +# Note: the special character '~' forces Make to invoke a shell. This
> > > > workaround
> > > > +# is needed because this issue was only fixed after GNU Make 4.2.1
> > > > release.
> > > > cc-cross-prefix = $(firstword $(foreach c, $(filter-out -%, $(1)), \
> > > > - $(if $(shell which $(c)gcc),
> > > > $(c
> > > > + $(if $(shell command -v $(c)gcc ~),
> > > > $(c
> > >
> > > I see a problem here:
> > > command -v foo bar
> > > could be deemed to be an error (extra argument).
> >
> > OK, the specification does not allow to pass arguments
> > with -v.
> >
> >
> > > You could use:
> > > $(shell sh -c "command -v $(c)gcc")
> > > or maybe:
> > > $(shell command$${x:+} -v $(c)gcc)
> >
> >
> > How about this?
> >
> > $(shell : ~; command -v $(c)gcc)
>
> Overcomplicated
>
> I've not looked at the list of 'special characters' in make,
> but I suspect any var
RE: [PATCH] kbuild: use more portable 'command -v' for cc-cross-prefix
From: Masahiro Yamada
> Sent: 03 June 2019 12:38
> Hi David,
>
> On Mon, Jun 3, 2019 at 8:14 PM David Laight 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.
> > >
> > > When I worked on commit bd55f96fa9fc ("kbuild: refactor cc-cross-prefix
> > > implementation"), I was eager to use 'command -v' but it did not work.
> > > (The reason is explained below.)
> > >
> > > I kept 'which' as before but got rid of '> /dev/null 2>&1' as I
> > > thought it was no longer needed. Sorry, I was wrong.
> > >
> > > It works well on my Ubuntu machine, but Alexey Brodkin reports annoying
> > > warnings from the 'which' on CentOS 7 when the given command is not
> > > found in the PATH environment.
> > >
> > > $ which foo
> > > which: no foo in
> > > (/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin)
> > >
> > > Given that behavior of 'which' is different on environment, I want
> > > to try 'command -v' again.
> > >
> > > The specification [1] clearly describes the behavior of 'command -v'
> > > when the given command is not found:
> > >
> > > Otherwise, no output shall be written and the exit status shall reflect
> > > that the name was not found.
> > >
> > > However, we need a little magic to use 'command -v' from Make.
> > >
> > > $(shell ...) passes the argument to a subshell for execution, and
> > > returns the standard output of the command.
> > >
> > > Here is a trick. GNU Make may optimize this by executing the command
> > > directly instead of forking a subshell, if no shell special characters
> > > are found in the command line and omitting the subshell will not
> > > change the behavior.
> > >
> > > In this case, no shell special character is used. So, Make will try
> > > to run the command directly. However, 'command' is a shell-builtin
> > > command. In fact, Make has a table of shell-builtin commands because
> > > it must spawn a subshell to execute them.
> > >
> > > Until recently, 'command' was missing in the table.
> > >
> > > This issue was fixed by the following commit:
> > >
> > > | commit 1af314465e5dfe3e8baa839a32a72e83c04f26ef
> > > | Author: Paul Smith
> > > | Date: Sun Nov 12 18:10:28 2017 -0500
> > > |
> > > | * job.c: Add "command" as a known shell built-in.
> > > |
> > > | This is not a POSIX shell built-in but it's common in UNIX shells.
> > > | Reported by Nick Bowler .
> > >
> > > This is not included in any released versions of Make yet.
> > > (But, some distributions may have back-ported the fix-up.)
> > >
> > > To trick Make and let it fork the subshell, I added a shell special
> > > character '~'. We may be able to get rid of this workaround someday,
> > > but it is very far into the future.
> > >
> > > [1] http://pubs.opengroup.org/onlinepubs/9699919799/utilities/command.html
> > >
> > > Fixes: bd55f96fa9fc ("kbuild: refactor cc-cross-prefix implementation")
> > > Cc: linux-stable # 5.1
> > > Reported-by: Alexey Brodkin
> > > Signed-off-by: Masahiro Yamada
> > > ---
> > >
> > > scripts/Kbuild.include | 5 -
> > > 1 file changed, 4 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> > > index 85d758233483..5a32ca80c3f6 100644
> > > --- a/scripts/Kbuild.include
> > > +++ b/scripts/Kbuild.include
> > > @@ -74,8 +74,11 @@ endef
> > > # Usage: CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu-
> > > m68k-linux-)
> > > # Return first where a gcc is found in PATH.
> > > # If no gcc found in PATH with listed prefixes return nothing
> > > +#
> > > +# Note: the special character '~' forces Make to invoke a shell. This
> > > workaround
> > > +# is needed because this issue was only fixed after GNU Make 4.2.1
> > > release.
> > > cc-cross-prefix = $(firstword $(foreach c, $(filter-out -%, $(1)), \
> > > - $(if $(shell which $(c)gcc), $(c
> > > + $(if $(shell command -v $(c)gcc ~), $(c
> >
> > I see a problem here:
> > command -v foo bar
> > could be deemed to be an error (extra argument).
>
> OK, the specification does not allow to pass arguments
> with -v.
>
>
> > You could use:
> > $(shell sh -c "command -v $(c)gcc")
> > or maybe:
> > $(shell command$${x:+} -v $(c)gcc)
>
>
> How about this?
>
> $(shell : ~; command -v $(c)gcc)
Overcomplicated
I've not looked at the list of 'special characters' in make,
but I suspect any variable expansion is enough.
Since ${x:+} always expands to the empty string (whether or
not 'x' is defined) it can't have any unfortunate side effects.
I'd comment as:
# Note: ${x:+} always expands to the empty string and forces all
# versions of make to actually exec $SHELL rather than try to
# directly execute the shell builti
RE: [PATCH] kbuild: use more portable 'command -v' for cc-cross-prefix
From: Masahiro Yamada
> Sent: 03 June 2019 12:45
> On Mon, Jun 3, 2019 at 8:16 PM David Laight 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.
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)
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Re: [PATCH] kbuild: use more portable 'command -v' for cc-cross-prefix
On Mon, Jun 3, 2019 at 8:16 PM David Laight 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.
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
# SPDX-License-Identifier: GPL-2.0
#
# Build U-Boot image when `mkimage' tool is available.
#
-MKIMAGE=$(type -path "${CROSS_COMPILE}mkimage")
+MKIMAGE=$(command -v "${CROSS_COMPILE}mkimage")
if [ -z "${MKIMAGE}" ]; then
- MKIMAGE=$(type -path mkimage)
+ MKIMAGE=$(command -v mkimage)
if [ -z "${MKIMAGE}" ]; then
# Doesn't exist
echo '"mkimage" command not found - U-Boot images will
not be built' >&2
--
Best Regards
Masahiro Yamada
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Re: [PATCH] kbuild: use more portable 'command -v' for cc-cross-prefix
Hi David,
On Mon, Jun 3, 2019 at 8:14 PM David Laight 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.
> >
> > When I worked on commit bd55f96fa9fc ("kbuild: refactor cc-cross-prefix
> > implementation"), I was eager to use 'command -v' but it did not work.
> > (The reason is explained below.)
> >
> > I kept 'which' as before but got rid of '> /dev/null 2>&1' as I
> > thought it was no longer needed. Sorry, I was wrong.
> >
> > It works well on my Ubuntu machine, but Alexey Brodkin reports annoying
> > warnings from the 'which' on CentOS 7 when the given command is not
> > found in the PATH environment.
> >
> > $ which foo
> > which: no foo in
> > (/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin)
> >
> > Given that behavior of 'which' is different on environment, I want
> > to try 'command -v' again.
> >
> > The specification [1] clearly describes the behavior of 'command -v'
> > when the given command is not found:
> >
> > Otherwise, no output shall be written and the exit status shall reflect
> > that the name was not found.
> >
> > However, we need a little magic to use 'command -v' from Make.
> >
> > $(shell ...) passes the argument to a subshell for execution, and
> > returns the standard output of the command.
> >
> > Here is a trick. GNU Make may optimize this by executing the command
> > directly instead of forking a subshell, if no shell special characters
> > are found in the command line and omitting the subshell will not
> > change the behavior.
> >
> > In this case, no shell special character is used. So, Make will try
> > to run the command directly. However, 'command' is a shell-builtin
> > command. In fact, Make has a table of shell-builtin commands because
> > it must spawn a subshell to execute them.
> >
> > Until recently, 'command' was missing in the table.
> >
> > This issue was fixed by the following commit:
> >
> > | commit 1af314465e5dfe3e8baa839a32a72e83c04f26ef
> > | Author: Paul Smith
> > | Date: Sun Nov 12 18:10:28 2017 -0500
> > |
> > | * job.c: Add "command" as a known shell built-in.
> > |
> > | This is not a POSIX shell built-in but it's common in UNIX shells.
> > | Reported by Nick Bowler .
> >
> > This is not included in any released versions of Make yet.
> > (But, some distributions may have back-ported the fix-up.)
> >
> > To trick Make and let it fork the subshell, I added a shell special
> > character '~'. We may be able to get rid of this workaround someday,
> > but it is very far into the future.
> >
> > [1] http://pubs.opengroup.org/onlinepubs/9699919799/utilities/command.html
> >
> > Fixes: bd55f96fa9fc ("kbuild: refactor cc-cross-prefix implementation")
> > Cc: linux-stable # 5.1
> > Reported-by: Alexey Brodkin
> > Signed-off-by: Masahiro Yamada
> > ---
> >
> > scripts/Kbuild.include | 5 -
> > 1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> > index 85d758233483..5a32ca80c3f6 100644
> > --- a/scripts/Kbuild.include
> > +++ b/scripts/Kbuild.include
> > @@ -74,8 +74,11 @@ endef
> > # Usage: CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu-
> > m68k-linux-)
> > # Return first where a gcc is found in PATH.
> > # If no gcc found in PATH with listed prefixes return nothing
> > +#
> > +# Note: the special character '~' forces Make to invoke a shell. This
> > workaround
> > +# is needed because this issue was only fixed after GNU Make 4.2.1 release.
> > cc-cross-prefix = $(firstword $(foreach c, $(filter-out -%, $(1)), \
> > - $(if $(shell which $(c)gcc), $(c
> > + $(if $(shell command -v $(c)gcc ~), $(c
>
> I see a problem here:
> command -v foo bar
> could be deemed to be an error (extra argument).
OK, the specification does not allow to pass arguments
with -v.
> You could use:
> $(shell sh -c "command -v $(c)gcc")
> or maybe:
> $(shell command$${x:+} -v $(c)gcc)
How about this?
$(shell : ~; command -v $(c)gcc)
--
Best Regards
Masahiro Yamada
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RE: [PATCH] kbuild: use more portable 'command -v' for cc-cross-prefix
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. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) ___ linux-snps-arc mailing list linux-snps-arc@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-snps-arc
RE: [PATCH] kbuild: use more portable 'command -v' for cc-cross-prefix
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.
>
> When I worked on commit bd55f96fa9fc ("kbuild: refactor cc-cross-prefix
> implementation"), I was eager to use 'command -v' but it did not work.
> (The reason is explained below.)
>
> I kept 'which' as before but got rid of '> /dev/null 2>&1' as I
> thought it was no longer needed. Sorry, I was wrong.
>
> It works well on my Ubuntu machine, but Alexey Brodkin reports annoying
> warnings from the 'which' on CentOS 7 when the given command is not
> found in the PATH environment.
>
> $ which foo
> which: no foo in
> (/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin)
>
> Given that behavior of 'which' is different on environment, I want
> to try 'command -v' again.
>
> The specification [1] clearly describes the behavior of 'command -v'
> when the given command is not found:
>
> Otherwise, no output shall be written and the exit status shall reflect
> that the name was not found.
>
> However, we need a little magic to use 'command -v' from Make.
>
> $(shell ...) passes the argument to a subshell for execution, and
> returns the standard output of the command.
>
> Here is a trick. GNU Make may optimize this by executing the command
> directly instead of forking a subshell, if no shell special characters
> are found in the command line and omitting the subshell will not
> change the behavior.
>
> In this case, no shell special character is used. So, Make will try
> to run the command directly. However, 'command' is a shell-builtin
> command. In fact, Make has a table of shell-builtin commands because
> it must spawn a subshell to execute them.
>
> Until recently, 'command' was missing in the table.
>
> This issue was fixed by the following commit:
>
> | commit 1af314465e5dfe3e8baa839a32a72e83c04f26ef
> | Author: Paul Smith
> | Date: Sun Nov 12 18:10:28 2017 -0500
> |
> | * job.c: Add "command" as a known shell built-in.
> |
> | This is not a POSIX shell built-in but it's common in UNIX shells.
> | Reported by Nick Bowler .
>
> This is not included in any released versions of Make yet.
> (But, some distributions may have back-ported the fix-up.)
>
> To trick Make and let it fork the subshell, I added a shell special
> character '~'. We may be able to get rid of this workaround someday,
> but it is very far into the future.
>
> [1] http://pubs.opengroup.org/onlinepubs/9699919799/utilities/command.html
>
> Fixes: bd55f96fa9fc ("kbuild: refactor cc-cross-prefix implementation")
> Cc: linux-stable # 5.1
> Reported-by: Alexey Brodkin
> Signed-off-by: Masahiro Yamada
> ---
>
> scripts/Kbuild.include | 5 -
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> index 85d758233483..5a32ca80c3f6 100644
> --- a/scripts/Kbuild.include
> +++ b/scripts/Kbuild.include
> @@ -74,8 +74,11 @@ endef
> # Usage: CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu-
> m68k-linux-)
> # Return first where a gcc is found in PATH.
> # If no gcc found in PATH with listed prefixes return nothing
> +#
> +# Note: the special character '~' forces Make to invoke a shell. This
> workaround
> +# is needed because this issue was only fixed after GNU Make 4.2.1 release.
> cc-cross-prefix = $(firstword $(foreach c, $(filter-out -%, $(1)), \
> - $(if $(shell which $(c)gcc), $(c
> + $(if $(shell command -v $(c)gcc ~), $(c
I see a problem here:
command -v foo bar
could be deemed to be an error (extra argument).
You could use:
$(shell sh -c "command -v $(c)gcc")
or maybe:
$(shell command$${x:+} -v $(c)gcc)
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT,
UK
Registration No: 1397386 (Wales)
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RE: [PATCH] kbuild: use more portable 'command -v' for cc-cross-prefix
Hi Masahiro-san,
> -Original Message-
> From: linux-snps-arc On Behalf
> Of Masahiro Yamada
> Sent: Monday, June 3, 2019 1:49 PM
> To: linux-kbu...@vger.kernel.org
> Cc: Michal Marek ; Vineet Gupta
> ; Alexey Brodkin
> ; linux-ker...@vger.kernel.org; linux-stable
> ; Masahiro
> Yamada ; linux-snps-arc@lists.infradead.org
> Subject: [PATCH] kbuild: use more portable 'command -v' for cc-cross-prefix
[snip]
> Fixes: bd55f96fa9fc ("kbuild: refactor cc-cross-prefix implementation")
> Cc: linux-stable # 5.1
> Reported-by: Alexey Brodkin
> Signed-off-by: Masahiro Yamada
> ---
Thanks for the prompt fix - it does the trick, now no junk in the console!
Tested-by: Alexey Brodkin
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