Re: [PATCH] MIPS: VDSO: Use same -m%-float cflag as the kernel proper

[Kevin Hilman <khilman@baylibre.com>]

Paul Burton <paul.burton@mips.com> writes:

> The MIPS VDSO build currently doesn't provide the -msoft-float flag to
> the compiler as the kernel proper does. This results in an attempt to
> use the compiler's default floating point configuration, which can be
> problematic in cases where this is incompatible with the target CPU's
> -march= flag. For example decstation_defconfig fails to build using
> toolchains in which gcc was configured --with-fp-32=xx with the
> following error:
>
>     LDS     arch/mips/vdso/vdso.lds
>   cc1: error: '-march=r3000' requires '-mfp32'
>   make[2]: *** [scripts/Makefile.build:379: arch/mips/vdso/vdso.lds] Error 1
>
> The kernel proper avoids this error because we build with the
> -msoft-float compiler flag, rather than using the compiler's default.
> Pass this flag through to the VDSO build so that it too becomes agnostic
> to the toolchain's floating point configuration.
>
> Note that this is filtered out from KBUILD_CFLAGS rather than simply
> always using -msoft-float such that if we switch the kernel to use
> -mno-float in the future the VDSO will automatically inherit the change.
>
> The VDSO doesn't actually include any floating point code, and its
> .MIPS.abiflags section is already manually generated to specify that
> it's compatible with any floating point ABI. As such this change should
> have no effect on the resulting VDSO, apart from fixing the build
> failure for affected toolchains.
>
> Signed-off-by: Paul Burton <paul.burton@mips.com>
> Reported-by: Kevin Hilman <khilman@baylibre.com>
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Cc: Maciej W. Rozycki <macro@linux-mips.org>
> References: https://lore.kernel.org/linux-mips/1477843551-21813-1-git-send-email-linux@roeck-us.nets/
> References: https://kernelci.org/build/id/5c4e4ae059b5142a249ad004/logs/

Tested-by: Kevin Hilman <khilman@baylibre.com>