FAILED: patch "[PATCH] MIPS: VDSO: Use same -m%-float cflag as the kernel proper" failed to apply to 4.4-stable tree

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 0648e50e548d881d025b9419a1a168753c8e2bf7 Mon Sep 17 00:00:00 2001
From: Paul Burton <[email protected]>
Date: Mon, 28 Jan 2019 22:21:17 +0000
Subject: [PATCH] MIPS: VDSO: Use same -m%-float cflag as the kernel proper

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.

References: https://lore.kernel.org/linux-mips/[email protected]/
References: https://kernelci.org/build/id/5c4e4ae059b5142a249ad004/logs/

index f6fd340e39c2..314949b2261d 100644
@@ -8,6 +8,7 @@ ccflags-vdso := \
 	$(filter -E%,$(KBUILD_CFLAGS)) \
 	$(filter -mmicromips,$(KBUILD_CFLAGS)) \
 	$(filter -march=%,$(KBUILD_CFLAGS)) \
+	$(filter -m%-float,$(KBUILD_CFLAGS)) \
 	-D__VDSO__
 
 ifdef CONFIG_CC_IS_CLANG