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SubjectRe: [PATCH v3 1/5] arm64: vdso32: Introduce COMPAT_CC_IS_GCC
On Thu, Sep 26, 2019 at 10:43:38PM +0100, Vincenzo Frascino wrote:
> 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@kernel.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
> ---
> arch/arm64/Kconfig | 5 ++++-
> arch/arm64/Makefile | 18 +++++-------------
> arch/arm64/kernel/vdso32/Makefile | 2 --
> 3 files changed, 9 insertions(+), 16 deletions(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 37c610963eee..0e5beb928af5 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_ARM_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_ARM_GCC
> + def_bool $(success,$(COMPATCC) --version | head -n 1 | grep -q "arm-.*-gcc")

I've seen toolchains where the first part of the tuple is "armv7-", so they
won't get detected here. However, do we really need to detect this? If
somebody passes a duff compiler, then the build will fail in the same way as
if they passed it to CROSS_COMPILE=.

I'd prefer to drop this check altogether.

Will

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