From: Nathan Chancellor <natechancellor@gmail.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
clang-built-linux@googlegroups.com,
Nathan Chancellor <natechancellor@gmail.com>,
Daniel Axtens <dja@axtens.net>
Subject: [PATCH v2] powerpc: Don't add -mabi= flags when building with Clang
Date: Tue, 20 Aug 2019 16:29:22 -0700 [thread overview]
Message-ID: <20190820232921.102673-1-natechancellor@gmail.com> (raw)
In-Reply-To: <20190818191321.58185-1-natechancellor@gmail.com>
When building pseries_defconfig, building vdso32 errors out:
error: unknown target ABI 'elfv1'
This happens because -m32 in clang changes the target to 32-bit,
which does not allow the ABI to be changed, as the setABI virtual
function is not overridden:
https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0-rc2/clang/include/clang/Basic/TargetInfo.h#L1073-L1078
https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0-rc2/clang/lib/Basic/Targets/PPC.h#L327-L365
Commit 4dc831aa8813 ("powerpc: Fix compiling a BE kernel with a
powerpc64le toolchain") added these flags to fix building big endian
kernels with a little endian GCC.
Clang doesn't need -mabi because the target triple controls the default
value. -mlittle-endian and -mbig-endian manipulate the triple into
either powerpc64-* or powerpc64le-*, which properly sets the default
ABI:
https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0-rc2/clang/lib/Driver/Driver.cpp#L450-L463
https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0-rc2/llvm/lib/Support/Triple.cpp#L1432-L1516
https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0-rc2/clang/lib/Basic/Targets/PPC.h#L377-L383
Adding a debug print out in the PPC64TargetInfo constructor after line
383 above shows this:
$ echo | ./clang -E --target=powerpc64-linux -mbig-endian -o /dev/null -
Default ABI: elfv1
$ echo | ./clang -E --target=powerpc64-linux -mlittle-endian -o /dev/null -
Default ABI: elfv2
$ echo | ./clang -E --target=powerpc64le-linux -mbig-endian -o /dev/null -
Default ABI: elfv1
$ echo | ./clang -E --target=powerpc64le-linux -mlittle-endian -o /dev/null -
Default ABI: elfv2
Don't specify -mabi when building with clang to avoid the build error
with -m32 and not change any code generation.
-mcall-aixdesc is not an implemented flag in clang so it can be
safely excluded as well, see commit 238abecde8ad ("powerpc: Don't
use gcc specific options on clang").
pseries_defconfig successfully builds after this patch and
powernv_defconfig and ppc44x_defconfig don't regress.
Link: https://github.com/ClangBuiltLinux/linux/issues/240
Reviewed-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
v1 -> v2:
* Improve commit message wording and explanation.
* Add Daniel's reviewed-by.
arch/powerpc/Makefile | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index c345b79414a9..971b04bc753d 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -93,11 +93,13 @@ MULTIPLEWORD := -mmultiple
endif
ifdef CONFIG_PPC64
+ifndef CONFIG_CC_IS_CLANG
cflags-$(CONFIG_CPU_BIG_ENDIAN) += $(call cc-option,-mabi=elfv1)
cflags-$(CONFIG_CPU_BIG_ENDIAN) += $(call cc-option,-mcall-aixdesc)
aflags-$(CONFIG_CPU_BIG_ENDIAN) += $(call cc-option,-mabi=elfv1)
aflags-$(CONFIG_CPU_LITTLE_ENDIAN) += -mabi=elfv2
endif
+endif
ifndef CONFIG_CC_IS_CLANG
cflags-$(CONFIG_CPU_LITTLE_ENDIAN) += -mno-strict-align
@@ -144,6 +146,7 @@ endif
endif
CFLAGS-$(CONFIG_PPC64) := $(call cc-option,-mtraceback=no)
+ifndef CONFIG_CC_IS_CLANG
ifdef CONFIG_CPU_LITTLE_ENDIAN
CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mabi=elfv2,$(call cc-option,-mcall-aixdesc))
AFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mabi=elfv2)
@@ -152,6 +155,7 @@ CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mabi=elfv1)
CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mcall-aixdesc)
AFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mabi=elfv1)
endif
+endif
CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mcmodel=medium,$(call cc-option,-mminimal-toc))
CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mno-pointers-to-nested-functions)
--
2.23.0
prev parent reply other threads:[~2019-08-20 23:30 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-18 19:13 [PATCH] powerpc: Don't add -mabi= flags when building with Clang Nathan Chancellor
2019-08-19 7:25 ` Daniel Axtens
2019-08-19 9:19 ` Segher Boessenkool
2019-08-20 3:15 ` Nathan Chancellor
2019-08-20 12:40 ` Segher Boessenkool
2019-08-20 17:58 ` Nathan Chancellor
2019-08-20 23:29 ` Nathan Chancellor [this message]
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