[PATCH v2 4/4] arm64: vdso32: require CROSS_COMPILE_COMPAT for gcc+bfd

[Nick Desaulniers]

Similar to
commit 231ad7f409f1 ("Makefile: infer --target from ARCH for CC=clang")
There really is no point in setting --target based on
$CROSS_COMPILE_COMPAT for clang when the integrated assembler is being
used, since
commit ef94340583ee ("arm64: vdso32: drop -no-integrated-as flag").

Allows COMPAT_VDSO to be selected without setting $CROSS_COMPILE_COMPAT
when using clang and lld together.

Before:
$ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make -j72 LLVM=1 defconfig
$ grep CONFIG_COMPAT_VDSO .config
CONFIG_COMPAT_VDSO=y
$ ARCH=arm64 make -j72 LLVM=1 defconfig
$ grep CONFIG_COMPAT_VDSO .config
$

After:
$ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make -j72 LLVM=1 defconfig
$ grep CONFIG_COMPAT_VDSO .config
CONFIG_COMPAT_VDSO=y
$ ARCH=arm64 make -j72 LLVM=1 defconfig
$ grep CONFIG_COMPAT_VDSO .config
CONFIG_COMPAT_VDSO=y

Reviewed-by: Nathan Chancellor <nathan at kernel.org>
Suggested-by: Nathan Chancellor <nathan at kernel.org>
Tested-by: Nathan Chancellor <nathan at kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers at google.com>
---
Changes v1 -> v2:
* Cite ef94340583ee as per Nathan.
* Add parens to Kconfig expression as per Nathan.
* Pick up Nathan's RB, TB, and SB tags.

 arch/arm64/Kconfig                |  3 ++-
 arch/arm64/kernel/vdso32/Makefile | 17 +++++------------
 2 files changed, 7 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 5c7ae4c3954b..f0f2c95aa4c8 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1264,7 +1264,8 @@ config KUSER_HELPERS
 
 config COMPAT_VDSO
 	bool "Enable vDSO for 32-bit applications"
-	depends on !CPU_BIG_ENDIAN && "$(CROSS_COMPILE_COMPAT)" != ""
+	depends on !CPU_BIG_ENDIAN
+	depends on (CC_IS_CLANG && LD_IS_LLD) || "$(CROSS_COMPILE_COMPAT)" != ""
 	select GENERIC_COMPAT_VDSO
 	default y
 	help
diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
index e478cebb9891..c8fec493a450 100644
--- a/arch/arm64/kernel/vdso32/Makefile
+++ b/arch/arm64/kernel/vdso32/Makefile
@@ -10,18 +10,15 @@ include $(srctree)/lib/vdso/Makefile
 
 # Same as cc-*option, but using CC_COMPAT instead of CC
 ifeq ($(CONFIG_CC_IS_CLANG), y)
-CC_COMPAT_CLANG_FLAGS := --target=$(notdir $(CROSS_COMPILE_COMPAT:%-=%))
-
 CC_COMPAT ?= $(CC)
-CC_COMPAT += $(CC_COMPAT_CLANG_FLAGS)
-
-ifneq ($(LLVM),)
-LD_COMPAT ?= $(LD)
+CC_COMPAT += --target=arm-linux-gnueabi
 else
-LD_COMPAT ?= $(CROSS_COMPILE_COMPAT)ld
+CC_COMPAT ?= $(CROSS_COMPILE_COMPAT)gcc
 endif
+
+ifeq ($(CONFIG_LD_IS_LLD), y)
+LD_COMPAT ?= $(LD)
 else
-CC_COMPAT ?= $(CROSS_COMPILE_COMPAT)gcc
 LD_COMPAT ?= $(CROSS_COMPILE_COMPAT)ld
 endif
 
@@ -45,10 +42,6 @@ VDSO_CPPFLAGS += $(LINUXINCLUDE)
 # Common C and assembly flags
 # From top-level Makefile
 VDSO_CAFLAGS := $(VDSO_CPPFLAGS)
-ifneq ($(shell $(CC_COMPAT) --version 2>&1 | head -n 1 | grep clang),)
-VDSO_CAFLAGS += --target=$(notdir $(CROSS_COMPILE_COMPAT:%-=%))
-endif
-
 VDSO_CAFLAGS += $(call cc32-option,-fno-PIE)
 ifdef CONFIG_DEBUG_INFO
 VDSO_CAFLAGS += -g
-- 
2.33.0.1079.g6e70778dc9-goog