[PATCH v2 1/4] arm64: vdso32: Introduce COMPAT_CC_IS_GCC

[Vincenzo Frascino]

As reported by Will Deacon the .config file and the generated
include/config/auto.conf can end up out of sync after a set of
commands since CONFIG_CROSS_COMPILE_COMPAT_VDSO is not updated
correctly.

The sequence can be reproduced as follows:

$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- defconfig
[...]
$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- menuconfig
[set CONFIG_CROSS_COMPILE_COMPAT_VDSO="arm-linux-gnueabihf-"]
$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-

Which results in:

arch/arm64/Makefile:62: CROSS_COMPILE_COMPAT not defined or empty,
the compat vDSO will not be built

even though the compat vDSO has been built:

$ file arch/arm64/kernel/vdso32/vdso.so
arch/arm64/kernel/vdso32/vdso.so: ELF 32-bit LSB pie executable, ARM,
EABI5 version 1 (SYSV), dynamically linked,
BuildID[sha1]=c67f6c786f2d2d6f86c71f708595594aa25247f6, stripped

A similar case that involves changing the configuration parameter multiple
times can be reconducted to the same family of problems.

The reason behind it comes from the fact that the master Makefile includes
that architecture Makefile twice, once before the syncconfig and one after.
Since the synchronization of the files happens only upon syncconfig, the
architecture Makefile included before this event does not see the change in
configuration.

As a consequence of this it is not possible to handle the cross compiler
definitions inside the architecture Makefile.

Address the problem removing CONFIG_CROSS_COMPILE_COMPAT_VDSO and moving
the detection of the correct compiler into Kconfig via COMPAT_CC_IS_GCC.

As a consequence of this it is not possible anymore to set the compat
cross compiler from menuconfig but it requires to be exported via
command line.

E.g.:

$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-
CROSS_COMPILE_COMPAT=arm-linux-gnueabihf

Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
---
 arch/arm64/Kconfig  |  5 ++++-
 arch/arm64/Makefile | 15 ++-------------
 2 files changed, 6 insertions(+), 14 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 37c610963eee..13e2d2e16af7 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -110,7 +110,7 @@ config ARM64
 	select GENERIC_STRNLEN_USER
 	select GENERIC_TIME_VSYSCALL
 	select GENERIC_GETTIMEOFDAY
-	select GENERIC_COMPAT_VDSO if (!CPU_BIG_ENDIAN && COMPAT)
+	select GENERIC_COMPAT_VDSO if (!CPU_BIG_ENDIAN && COMPAT && COMPATCC_IS_GCC)
 	select HANDLE_DOMAIN_IRQ
 	select HARDIRQS_SW_RESEND
 	select HAVE_PCI
@@ -313,6 +313,9 @@ config KASAN_SHADOW_OFFSET
 	default 0xeffffff900000000 if ARM64_VA_BITS_36 && KASAN_SW_TAGS
 	default 0xffffffffffffffff
 
+config COMPATCC_IS_GCC
+	def_bool $(success,$(CROSS_COMPILE_COMPAT)gcc --version | head -n 1 | grep -q arm)
+
 source "arch/arm64/Kconfig.platforms"
 
 menu "Kernel Features"
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 84a3d502c5a5..34f53eb11878 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -54,19 +54,8 @@ $(warning Detected assembler with broken .inst; disassembly will be unreliable)
 endif
 
 ifeq ($(CONFIG_GENERIC_COMPAT_VDSO), y)
-  CROSS_COMPILE_COMPAT ?= $(CONFIG_CROSS_COMPILE_COMPAT_VDSO:"%"=%)
-
-  ifeq ($(CONFIG_CC_IS_CLANG), y)
-    $(warning CROSS_COMPILE_COMPAT is clang, the compat vDSO will not be built)
-  else ifeq ($(strip $(CROSS_COMPILE_COMPAT)),)
-    $(warning CROSS_COMPILE_COMPAT not defined or empty, the compat vDSO will not be built)
-  else ifeq ($(shell which $(CROSS_COMPILE_COMPAT)gcc 2> /dev/null),)
-    $(error $(CROSS_COMPILE_COMPAT)gcc not found, check CROSS_COMPILE_COMPAT)
-  else
-    export CROSS_COMPILE_COMPAT
-    export CONFIG_COMPAT_VDSO := y
-    compat_vdso := -DCONFIG_COMPAT_VDSO=1
-  endif
+  export CONFIG_COMPAT_VDSO := y
+  compat_vdso := -DCONFIG_COMPAT_VDSO=1
 endif
 
 KBUILD_CFLAGS	+= -mgeneral-regs-only $(lseinstr) $(brokengasinst)	\
-- 
2.23.0