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Date: Wed, 19 Aug 2015 17:41:40 +0200
From: Michal Marek <mmarek@...e.cz>
To: Anton Blanchard <anton@...ba.org>
Cc: Behan Webster <behanw@...verseincode.com>,
Paul Cercueil <paul@...pouillou.net>,
linux-kbuild@...r.kernel.org,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v2] Makefile: Fix detection of clang when cross-compiling
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@...pouillou.net
> > <mailto:paul@...pouillou.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@...e.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@...verseincode.com>
Reported-by: Anton Blanchard <anton@...ba.org>
Signed-off-by: Michal Marek <mmarek@...e.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
--
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