[PATCH v2] Makefile: Fix detection of clang when cross-compiling

[PATCH v2] Makefile: Fix detection of clang when cross-compiling

[Paul Cercueil]

When the host's C compiler is clang, and when attempting to
cross-compile Linux e.g. to MIPS with mipsel-linux-gcc, the Makefile
would incorrectly detect the use of clang, which resulted in
clang-specific flags being passed to mipsel-linux-gcc.

This can be verified under Debian by installing the "clang" package,
and then using it as the default compiler with:
sudo update-alternatives --config cc

This patch moves the detection of clang after the $(CC) variable is
initialized to the name of the cross-compiler, so that the check applies
to the cross-compiler and not the host's C compiler.

v2: Move the detection of clang after the inclusion of the
arch/*/Makefile (as they might set $(CROSS_COMPILE))

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
---
 Makefile | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/Makefile b/Makefile
index fbd43bf..e1e8c7e 100644
--- a/Makefile
+++ b/Makefile
@@ -335,15 +335,6 @@ endif
 export KBUILD_MODULES KBUILD_BUILTIN
 export KBUILD_CHECKSRC KBUILD_SRC KBUILD_EXTMOD
 
-ifneq ($(CC),)
-ifeq ($(shell $(CC) -v 2>&1 | grep -c "clang version"), 1)
-COMPILER := clang
-else
-COMPILER := gcc
-endif
-export COMPILER
-endif
-
 # Look for make include files relative to root of kernel src
 MAKEFLAGS += --include-dir=$(srctree)
 
@@ -673,6 +664,13 @@ endif
 endif
 KBUILD_CFLAGS += $(stackp-flag)
 
+ifeq ($(shell $(CC) -v 2>&1 | grep -c "clang version"), 1)
+COMPILER := clang
+else
+COMPILER := gcc
+endif
+export COMPILER
+
 ifeq ($(COMPILER),clang)
 KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,)
 KBUILD_CPPFLAGS += $(call cc-option,-Wno-unknown-warning-option,)
-- 
2.1.4

Re: [PATCH v2] Makefile: Fix detection of clang when cross-compiling

[Michal Marek]

On Fri, Apr 17, 2015 at 11:35:04PM +0200, Paul Cercueil wrote:
> When the host's C compiler is clang, and when attempting to
> cross-compile Linux e.g. to MIPS with mipsel-linux-gcc, the Makefile
> would incorrectly detect the use of clang, which resulted in
> clang-specific flags being passed to mipsel-linux-gcc.
> 
> This can be verified under Debian by installing the "clang" package,
> and then using it as the default compiler with:
> sudo update-alternatives --config cc
> 
> This patch moves the detection of clang after the $(CC) variable is
> initialized to the name of the cross-compiler, so that the check applies
> to the cross-compiler and not the host's C compiler.
> 
> v2: Move the detection of clang after the inclusion of the
> arch/*/Makefile (as they might set $(CROSS_COMPILE))
> 
> Signed-off-by: Paul Cercueil <paul@crapouillou.net>

Applied to kbuild.git#kbuild. I will push it after v4.1-rc1 becomes
available, though.

Michal

Re: [PATCH v2] Makefile: Fix detection of clang when cross-compiling

[Behan Webster]

Resent since gmail HTML-ified my previous email...

On Wed, Apr 22, 2015 at 7:33 AM, Michal Marek <mmarek@suse.cz 
<mailto:mmarek@suse.cz>> wrote:

    On Fri, Apr 17, 2015 at 11:35:04PM +0200, Paul Cercueil wrote:
     > When the host's C compiler is clang, and when attempting to
     > cross-compile Linux e.g. to MIPS with mipsel-linux-gcc, the Makefile
     > would incorrectly detect the use of clang, which resulted in
     > clang-specific flags being passed to mipsel-linux-gcc.
     >
     > This can be verified under Debian by installing the "clang" package,
     > and then using it as the default compiler with:
     > sudo update-alternatives --config cc
     >
     > This patch moves the detection of clang after the $(CC) variable is
     > initialized to the name of the cross-compiler, so that the check
    applies
     > to the cross-compiler and not the host's C compiler.
     >
     > v2: Move the detection of clang after the inclusion of the
     > arch/*/Makefile (as they might set $(CROSS_COMPILE))
     >
     > Signed-off-by: Paul Cercueil <paul@crapouillou.net
    <mailto:paul@crapouillou.net>>

    Applied to kbuild.git#kbuild. I will push it after v4.1-rc1 becomes
    available, though.


Drat. I wish I saw this earlier.

This breaks patches which check for the value of COMPILER in 
arch/*/Makefile. This detection must be performed before the inclusion 
of the arch Makefile.

Can I move this to after the initialization of CC but before the include?

I'm not sure that being able to define the default compiler per arch is 
necessary. But I know I need to be able to add arch specific flags for 
clang.

Behan

-- 
Behan Webster
behanw@converseincode.com <mailto:behanw@converseincode.com>

Re: [PATCH v2] Makefile: Fix detection of clang when cross-compiling

[Anton Blanchard]

Hi,

>      > When the host's C compiler is clang, and when attempting to
>      > cross-compile Linux e.g. to MIPS with mipsel-linux-gcc, the
>      > Makefile would incorrectly detect the use of clang, which
>      > resulted in clang-specific flags being passed to
>      > mipsel-linux-gcc.
>      >
>      > This can be verified under Debian by installing the "clang"
>      > package, and then using it as the default compiler with:
>      > sudo update-alternatives --config cc
>      >
>      > This patch moves the detection of clang after the $(CC)
>      > variable is initialized to the name of the cross-compiler, so
>      > that the check applies
>      > to the cross-compiler and not the host's C compiler.
>      >
>      > v2: Move the detection of clang after the inclusion of the
>      > arch/*/Makefile (as they might set $(CROSS_COMPILE))
>      >
>      > Signed-off-by: Paul Cercueil <paul@crapouillou.net
>     <mailto:paul@crapouillou.net>>
> 
>     Applied to kbuild.git#kbuild. I will push it after v4.1-rc1
>     becomes available, though.
> 
> Drat. I wish I saw this earlier.
> 
> This breaks patches which check for the value of COMPILER in 
> arch/*/Makefile. This detection must be performed before the
> inclusion of the arch Makefile.
> 
> Can I move this to after the initialization of CC but before the
> include?
> 
> I'm not sure that being able to define the default compiler per arch
> is necessary. But I know I need to be able to add arch specific flags
> for clang.

I can confirm the patch breaks ppc64le clang builds.

Anton

Re: [PATCH v2] Makefile: Fix detection of clang when cross-compiling

[Michal Marek]

On Mon, Jul 13, 2015 at 08:59:33PM +1000, Anton Blanchard wrote:
> Hi,
> 
> >      > When the host's C compiler is clang, and when attempting to
> >      > cross-compile Linux e.g. to MIPS with mipsel-linux-gcc, the
> >      > Makefile would incorrectly detect the use of clang, which
> >      > resulted in clang-specific flags being passed to
> >      > mipsel-linux-gcc.
> >      >
> >      > This can be verified under Debian by installing the "clang"
> >      > package, and then using it as the default compiler with:
> >      > sudo update-alternatives --config cc
> >      >
> >      > This patch moves the detection of clang after the $(CC)
> >      > variable is initialized to the name of the cross-compiler, so
> >      > that the check applies
> >      > to the cross-compiler and not the host's C compiler.
> >      >
> >      > v2: Move the detection of clang after the inclusion of the
> >      > arch/*/Makefile (as they might set $(CROSS_COMPILE))
> >      >
> >      > Signed-off-by: Paul Cercueil <paul@crapouillou.net
> >     <mailto:paul@crapouillou.net>>
> > 
> >     Applied to kbuild.git#kbuild. I will push it after v4.1-rc1
> >     becomes available, though.
> > 
> > Drat. I wish I saw this earlier.
> > 
> > This breaks patches which check for the value of COMPILER in 
> > arch/*/Makefile. This detection must be performed before the
> > inclusion of the arch Makefile.
> > 
> > Can I move this to after the initialization of CC but before the
> > include?
> > 
> > I'm not sure that being able to define the default compiler per arch
> > is necessary. But I know I need to be able to add arch specific flags
> > for clang.
> 
> I can confirm the patch breaks ppc64le clang builds.

Can you try the (untested) patch below?


From 49bb3e66a9a7fc3685fb070bdfd31f2c3d78cc87 Mon Sep 17 00:00:00 2001
From: Michal Marek <mmarek@suse.com>
Date: Wed, 19 Aug 2015 17:36:41 +0200
Subject: [PATCH] kbuild: Fix clang detection

We cannot detect clang before including the arch Makefile, because that
can set the default cross compiler. We also cannot detect clang after
including the arch Makefile, because powerpc wants to know about clang.
Solve this by using an deferred variable. This costs us a few shell
invocations, but this is only a constant number.

Reported-by: Behan Webster <behanw@converseincode.com>
Reported-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michal Marek <mmarek@suse.com>
---
 Makefile                   | 9 +--------
 arch/powerpc/Makefile      | 8 ++++----
 scripts/Kbuild.include     | 4 ++++
 scripts/Makefile.extrawarn | 2 +-
 4 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/Makefile b/Makefile
index 13270c0..5ccbb58 100644
--- a/Makefile
+++ b/Makefile
@@ -661,14 +661,7 @@ endif
 endif
 KBUILD_CFLAGS += $(stackp-flag)
 
-ifeq ($(shell $(CC) -v 2>&1 | grep -c "clang version"), 1)
-COMPILER := clang
-else
-COMPILER := gcc
-endif
-export COMPILER
-
-ifeq ($(COMPILER),clang)
+ifeq ($(cc-name),clang)
 KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,)
 KBUILD_CPPFLAGS += $(call cc-option,-Wno-unknown-warning-option,)
 KBUILD_CFLAGS += $(call cc-disable-warning, unused-variable)
diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 05f464e..dfe88896 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -67,7 +67,7 @@ UTS_MACHINE := $(OLDARCH)
 
 ifeq ($(CONFIG_CPU_LITTLE_ENDIAN),y)
 override CC	+= -mlittle-endian
-ifneq ($(COMPILER),clang)
+ifneq ($(cc-name),clang)
 override CC	+= -mno-strict-align
 endif
 override AS	+= -mlittle-endian
@@ -333,7 +333,7 @@ TOUT	:= .tmp_gas_check
 # - Require gcc 4.0 or above on 64-bit
 # - gcc-4.2.0 has issues compiling modules on 64-bit
 checkbin:
-	@if test "${COMPILER}" != "clang" \
+	@if test "$(cc-name)" != "clang" \
 	    && test "$(cc-version)" = "0304" ; then \
 		if ! /bin/echo mftb 5 | $(AS) -v -mppc -many -o $(TOUT) >/dev/null 2>&1 ; then \
 			echo -n '*** ${VERSION}.${PATCHLEVEL} kernels no longer build '; \
@@ -342,14 +342,14 @@ checkbin:
 			false; \
 		fi ; \
 	fi
-	@if test "${COMPILER}" != "clang" \
+	@if test "$(cc-name)" != "clang" \
 	    && test "$(cc-version)" -lt "0400" \
 	    && test "x${CONFIG_PPC64}" = "xy" ; then \
                 echo -n "Sorry, GCC v4.0 or above is required to build " ; \
                 echo "the 64-bit powerpc kernel." ; \
                 false ; \
         fi
-	@if test "${COMPILER}" != "clang" \
+	@if test "$(cc-name)" != "clang" \
 	    && test "$(cc-fullversion)" = "040200" \
 	    && test "x${CONFIG_MODULES}${CONFIG_PPC64}" = "xyy" ; then \
 		echo -n '*** GCC-4.2.0 cannot compile the 64-bit powerpc ' ; \
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index d3437b8..3523df6 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -128,6 +128,10 @@ cc-option-align = $(subst -functions=0,,\
 cc-disable-warning = $(call try-run,\
 	$(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) -W$(strip $(1)) -c -x c /dev/null -o "$$TMP",-Wno-$(strip $(1)))
 
+# cc-name
+# Expands to either gcc or clang
+cc-name = $(shell $(CC) -v 2>&1 | grep -q "clang version" && echo clang || echo gcc)
+
 # cc-version
 cc-version = $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh $(CC))
 
diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index f734033..4efedcb 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -56,7 +56,7 @@ endif
 KBUILD_CFLAGS += $(warning)
 else
 
-ifeq ($(COMPILER),clang)
+ifeq ($(cc-name),clang)
 KBUILD_CFLAGS += $(call cc-disable-warning, initializer-overrides)
 KBUILD_CFLAGS += $(call cc-disable-warning, unused-value)
 KBUILD_CFLAGS += $(call cc-disable-warning, format)
-- 
2.1.4

Re: [PATCH v2] Makefile: Fix detection of clang when cross-compiling

[Behan Webster]

On 08/19/15 08:41, Michal Marek wrote:
> On Mon, Jul 13, 2015 at 08:59:33PM +1000, Anton Blanchard wrote:
>> Hi,
>>
>>>       > When the host's C compiler is clang, and when attempting to
>>>       > cross-compile Linux e.g. to MIPS with mipsel-linux-gcc, the
>>>       > Makefile would incorrectly detect the use of clang, which
>>>       > resulted in clang-specific flags being passed to
>>>       > mipsel-linux-gcc.
>>>       >
>>>       > This can be verified under Debian by installing the "clang"
>>>       > package, and then using it as the default compiler with:
>>>       > sudo update-alternatives --config cc
>>>       >
>>>       > This patch moves the detection of clang after the $(CC)
>>>       > variable is initialized to the name of the cross-compiler, so
>>>       > that the check applies
>>>       > to the cross-compiler and not the host's C compiler.
>>>       >
>>>       > v2: Move the detection of clang after the inclusion of the
>>>       > arch/*/Makefile (as they might set $(CROSS_COMPILE))
>>>       >
>>>       > Signed-off-by: Paul Cercueil <paul@crapouillou.net
>>>      <mailto:paul@crapouillou.net>>
>>>
>>>      Applied to kbuild.git#kbuild. I will push it after v4.1-rc1
>>>      becomes available, though.
>>>
>>> Drat. I wish I saw this earlier.
>>>
>>> This breaks patches which check for the value of COMPILER in
>>> arch/*/Makefile. This detection must be performed before the
>>> inclusion of the arch Makefile.
>>>
>>> Can I move this to after the initialization of CC but before the
>>> include?
>>>
>>> I'm not sure that being able to define the default compiler per arch
>>> is necessary. But I know I need to be able to add arch specific flags
>>> for clang.
>> I can confirm the patch breaks ppc64le clang builds.
> Can you try the (untested) patch below?
>
>
>  From 49bb3e66a9a7fc3685fb070bdfd31f2c3d78cc87 Mon Sep 17 00:00:00 2001
> From: Michal Marek <mmarek@suse.com>
> Date: Wed, 19 Aug 2015 17:36:41 +0200
> Subject: [PATCH] kbuild: Fix clang detection
>
> We cannot detect clang before including the arch Makefile, because that
> can set the default cross compiler. We also cannot detect clang after
> including the arch Makefile, because powerpc wants to know about clang.
> Solve this by using an deferred variable. This costs us a few shell
> invocations, but this is only a constant number.
>
> Reported-by: Behan Webster <behanw@converseincode.com>
> Reported-by: Anton Blanchard <anton@samba.org>
> Signed-off-by: Michal Marek <mmarek@suse.com>
> ---
>   Makefile                   | 9 +--------
>   arch/powerpc/Makefile      | 8 ++++----
>   scripts/Kbuild.include     | 4 ++++
>   scripts/Makefile.extrawarn | 2 +-
>   4 files changed, 10 insertions(+), 13 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 13270c0..5ccbb58 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -661,14 +661,7 @@ endif
>   endif
>   KBUILD_CFLAGS += $(stackp-flag)
>   
> -ifeq ($(shell $(CC) -v 2>&1 | grep -c "clang version"), 1)
> -COMPILER := clang
> -else
> -COMPILER := gcc
> -endif
> -export COMPILER
> -
> -ifeq ($(COMPILER),clang)
> +ifeq ($(cc-name),clang)
>   KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,)
>   KBUILD_CPPFLAGS += $(call cc-option,-Wno-unknown-warning-option,)
>   KBUILD_CFLAGS += $(call cc-disable-warning, unused-variable)
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index 05f464e..dfe88896 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -67,7 +67,7 @@ UTS_MACHINE := $(OLDARCH)
>   
>   ifeq ($(CONFIG_CPU_LITTLE_ENDIAN),y)
>   override CC	+= -mlittle-endian
> -ifneq ($(COMPILER),clang)
> +ifneq ($(cc-name),clang)
>   override CC	+= -mno-strict-align
>   endif
>   override AS	+= -mlittle-endian
> @@ -333,7 +333,7 @@ TOUT	:= .tmp_gas_check
>   # - Require gcc 4.0 or above on 64-bit
>   # - gcc-4.2.0 has issues compiling modules on 64-bit
>   checkbin:
> -	@if test "${COMPILER}" != "clang" \
> +	@if test "$(cc-name)" != "clang" \
>   	    && test "$(cc-version)" = "0304" ; then \
>   		if ! /bin/echo mftb 5 | $(AS) -v -mppc -many -o $(TOUT) >/dev/null 2>&1 ; then \
>   			echo -n '*** ${VERSION}.${PATCHLEVEL} kernels no longer build '; \
> @@ -342,14 +342,14 @@ checkbin:
>   			false; \
>   		fi ; \
>   	fi
> -	@if test "${COMPILER}" != "clang" \
> +	@if test "$(cc-name)" != "clang" \
>   	    && test "$(cc-version)" -lt "0400" \
>   	    && test "x${CONFIG_PPC64}" = "xy" ; then \
>                   echo -n "Sorry, GCC v4.0 or above is required to build " ; \
>                   echo "the 64-bit powerpc kernel." ; \
>                   false ; \
>           fi
> -	@if test "${COMPILER}" != "clang" \
> +	@if test "$(cc-name)" != "clang" \
>   	    && test "$(cc-fullversion)" = "040200" \
>   	    && test "x${CONFIG_MODULES}${CONFIG_PPC64}" = "xyy" ; then \
>   		echo -n '*** GCC-4.2.0 cannot compile the 64-bit powerpc ' ; \
> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> index d3437b8..3523df6 100644
> --- a/scripts/Kbuild.include
> +++ b/scripts/Kbuild.include
> @@ -128,6 +128,10 @@ cc-option-align = $(subst -functions=0,,\
>   cc-disable-warning = $(call try-run,\
>   	$(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) -W$(strip $(1)) -c -x c /dev/null -o "$$TMP",-Wno-$(strip $(1)))
>   
> +# cc-name
> +# Expands to either gcc or clang
> +cc-name = $(shell $(CC) -v 2>&1 | grep -q "clang version" && echo clang || echo gcc)
> +
>   # cc-version
>   cc-version = $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh $(CC))
>   
> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> index f734033..4efedcb 100644
> --- a/scripts/Makefile.extrawarn
> +++ b/scripts/Makefile.extrawarn
> @@ -56,7 +56,7 @@ endif
>   KBUILD_CFLAGS += $(warning)
>   else
>   
> -ifeq ($(COMPILER),clang)
> +ifeq ($(cc-name),clang)
>   KBUILD_CFLAGS += $(call cc-disable-warning, initializer-overrides)
>   KBUILD_CFLAGS += $(call cc-disable-warning, unused-value)
>   KBUILD_CFLAGS += $(call cc-disable-warning, format)

Is there any reason you renamed COMPILER? Because it breaks all the 
other patches we have queued up which use it for cross compiling.

And aren't we supposed to use all caps for variable names?

This doesn't only break powerpc, it breaks arm, aarch64 and clang work 
that's being done on MIPS malta.

The big reason I wrote it the way I did was so other compilers could be 
added as well (as if-then-else stanzas).

I understand that the initial issue was that if /usr/bin/cc was clang 
things broke for MIPS, but that's just a temporal problem as we upstream 
clang support. Using gcc in the case were clang is the default compiler 
just muddies the waters IMHO. Wouldn't it be better to get people to 
explicitly specify the use of gcc on platforms which use clang by default?

     make CC=gcc

Which is similar to what we have to do to use clang on platforms which 
default to gcc. (make CC=clang)

In many ways I'd prefer to see ee4eb20dbce91751c248399e8a0cf9b8813adf5a 
reverted.

I just can't help thinking this is making things way more complicated 
than necessary.

Behan


-- 
Behan Webster
behanw@converseincode.com

Re: [PATCH v2] Makefile: Fix detection of clang when cross-compiling

[Michal Marek]

On 2015-08-27 03:49, Behan Webster wrote:
> 
> On 08/19/15 08:41, Michal Marek wrote:
>>  From 49bb3e66a9a7fc3685fb070bdfd31f2c3d78cc87 Mon Sep 17 00:00:00 2001
>> From: Michal Marek <mmarek@suse.com>
>> Date: Wed, 19 Aug 2015 17:36:41 +0200
>> Subject: [PATCH] kbuild: Fix clang detection
>>
>> We cannot detect clang before including the arch Makefile, because that
>> can set the default cross compiler. We also cannot detect clang after
>> including the arch Makefile, because powerpc wants to know about clang.
>> Solve this by using an deferred variable. This costs us a few shell
>> invocations, but this is only a constant number.
>>
>> Reported-by: Behan Webster <behanw@converseincode.com>
>> Reported-by: Anton Blanchard <anton@samba.org>
>> Signed-off-by: Michal Marek <mmarek@suse.com>
>> ---
>>   Makefile                   | 9 +--------
>>   arch/powerpc/Makefile      | 8 ++++----
>>   scripts/Kbuild.include     | 4 ++++
>>   scripts/Makefile.extrawarn | 2 +-
>>   4 files changed, 10 insertions(+), 13 deletions(-)
>>
>> diff --git a/Makefile b/Makefile
>> index 13270c0..5ccbb58 100644
>> --- a/Makefile
>> +++ b/Makefile
>> @@ -661,14 +661,7 @@ endif
>>   endif
>>   KBUILD_CFLAGS += $(stackp-flag)
>>   
>> -ifeq ($(shell $(CC) -v 2>&1 | grep -c "clang version"), 1)
>> -COMPILER := clang
>> -else
>> -COMPILER := gcc
>> -endif
>> -export COMPILER
>> -
>> -ifeq ($(COMPILER),clang)
>> +ifeq ($(cc-name),clang)
>>   KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,)
>>   KBUILD_CPPFLAGS += $(call cc-option,-Wno-unknown-warning-option,)
>>   KBUILD_CFLAGS += $(call cc-disable-warning, unused-variable)
>> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
>> index 05f464e..dfe88896 100644
>> --- a/arch/powerpc/Makefile
>> +++ b/arch/powerpc/Makefile
>> @@ -67,7 +67,7 @@ UTS_MACHINE := $(OLDARCH)
>>   
>>   ifeq ($(CONFIG_CPU_LITTLE_ENDIAN),y)
>>   override CC	+= -mlittle-endian
>> -ifneq ($(COMPILER),clang)
>> +ifneq ($(cc-name),clang)
>>   override CC	+= -mno-strict-align
>>   endif
>>   override AS	+= -mlittle-endian
>> @@ -333,7 +333,7 @@ TOUT	:= .tmp_gas_check
>>   # - Require gcc 4.0 or above on 64-bit
>>   # - gcc-4.2.0 has issues compiling modules on 64-bit
>>   checkbin:
>> -	@if test "${COMPILER}" != "clang" \
>> +	@if test "$(cc-name)" != "clang" \
>>   	    && test "$(cc-version)" = "0304" ; then \
>>   		if ! /bin/echo mftb 5 | $(AS) -v -mppc -many -o $(TOUT) >/dev/null 2>&1 ; then \
>>   			echo -n '*** ${VERSION}.${PATCHLEVEL} kernels no longer build '; \
>> @@ -342,14 +342,14 @@ checkbin:
>>   			false; \
>>   		fi ; \
>>   	fi
>> -	@if test "${COMPILER}" != "clang" \
>> +	@if test "$(cc-name)" != "clang" \
>>   	    && test "$(cc-version)" -lt "0400" \
>>   	    && test "x${CONFIG_PPC64}" = "xy" ; then \
>>                   echo -n "Sorry, GCC v4.0 or above is required to build " ; \
>>                   echo "the 64-bit powerpc kernel." ; \
>>                   false ; \
>>           fi
>> -	@if test "${COMPILER}" != "clang" \
>> +	@if test "$(cc-name)" != "clang" \
>>   	    && test "$(cc-fullversion)" = "040200" \
>>   	    && test "x${CONFIG_MODULES}${CONFIG_PPC64}" = "xyy" ; then \
>>   		echo -n '*** GCC-4.2.0 cannot compile the 64-bit powerpc ' ; \
>> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
>> index d3437b8..3523df6 100644
>> --- a/scripts/Kbuild.include
>> +++ b/scripts/Kbuild.include
>> @@ -128,6 +128,10 @@ cc-option-align = $(subst -functions=0,,\
>>   cc-disable-warning = $(call try-run,\
>>   	$(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) -W$(strip $(1)) -c -x c /dev/null -o "$$TMP",-Wno-$(strip $(1)))
>>   
>> +# cc-name
>> +# Expands to either gcc or clang
>> +cc-name = $(shell $(CC) -v 2>&1 | grep -q "clang version" && echo clang || echo gcc)
>> +
>>   # cc-version
>>   cc-version = $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh $(CC))
>>   
>> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
>> index f734033..4efedcb 100644
>> --- a/scripts/Makefile.extrawarn
>> +++ b/scripts/Makefile.extrawarn
>> @@ -56,7 +56,7 @@ endif
>>   KBUILD_CFLAGS += $(warning)
>>   else
>>   
>> -ifeq ($(COMPILER),clang)
>> +ifeq ($(cc-name),clang)
>>   KBUILD_CFLAGS += $(call cc-disable-warning, initializer-overrides)
>>   KBUILD_CFLAGS += $(call cc-disable-warning, unused-value)
>>   KBUILD_CFLAGS += $(call cc-disable-warning, format)
> 
> Is there any reason you renamed COMPILER? Because it breaks all the 
> other patches we have queued up which use it for cross compiling.
> 
> And aren't we supposed to use all caps for variable names?

It more like a function now and is consistent with the other cc-*
definitions in scripts/Kbuild.include.


> This doesn't only break powerpc, it breaks arm, aarch64 and clang work 
> that's being done on MIPS malta.

So do a s/COMPILER/cc-name/ ? You can merge my patch into your tree to
avoid a dependency on the kbuild tree.


> The big reason I wrote it the way I did was so other compilers could be 
> added as well (as if-then-else stanzas).
> 
> I understand that the initial issue was that if /usr/bin/cc was clang 
> things broke for MIPS, but that's just a temporal problem as we upstream 
> clang support.

I don't think so. Arch Makefiles are allowed to override the default
value of $(CC) and until then, it cannot be used.


> In many ways I'd prefer to see ee4eb20dbce91751c248399e8a0cf9b8813adf5a 
> reverted.

This just brings back the original problem.

Michal

Re: [PATCH v2] Makefile: Fix detection of clang when cross-compiling

[Michal Marek]

On 2015-08-27 10:37, Michal Marek wrote:
> On 2015-08-27 03:49, Behan Webster wrote:
>> Is there any reason you renamed COMPILER? Because it breaks all the 
>> other patches we have queued up which use it for cross compiling.
>>
>> And aren't we supposed to use all caps for variable names?
> 
> It more like a function now and is consistent with the other cc-*
> definitions in scripts/Kbuild.include.
> 
> 
>> This doesn't only break powerpc, it breaks arm, aarch64 and clang work 
>> that's being done on MIPS malta.
> 
> So do a s/COMPILER/cc-name/ ? You can merge my patch into your tree to
> avoid a dependency on the kbuild tree.

Since I haven't seen any further uses of the $(CLANG) variable in
linux-next, I applied the patch to kbuild.git now.

Michal