Messages in this thread | | | From | Linus Walleij <> | Date | Thu, 21 Dec 2017 21:02:45 +0100 | Subject | Re: [PATCH, RFT] ARM: use --fix-v4bx to allow building ARMv4 with future gcc |
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On Thu, Dec 21, 2017 at 6:02 PM, Arnd Bergmann <arnd@arndb.de> wrote: > On Thu, Dec 21, 2017 at 5:57 PM, Linus Walleij <linus.walleij@linaro.org> wrote: >> On Wed, Dec 20, 2017 at 2:00 PM, Arnd Bergmann <arnd@arndb.de> wrote: >> >>> gcc-6.0 and later marks support for ARMv3 and ARMv4 as 'deprecated', >>> meaning that this is expected to be removed at some point in the future, >>> with gcc-8.0 as the earliest. >>> >>> When building the kernel, the difference between ARMv4 and ARMv4T >>> is relatively small because the kernel never runs THUMB instructions >>> on ARMv4T and does not need any support for interworking. >>> >>> For any future compiler that does not support -march=armv4, we now >>> fall back to -march=armv4t as the architecture level selection, >>> but keep using -march=armv4 by default as long as that is supported >>> by the compiler. >>> >>> Similarly, the -mtune=strongarm110 and -mtune=strongarm1100 options >>> will go away at the same time as -march=armv4, so this adds a check >>> to see if the compiler supports them, falling back to no -mtune >>> option otherwise. >>> >>> Compiling with -march=armv4t leads the compiler to using 'bx reg' >>> instructions instead of 'mov pc,reg'. This is not supported on >>> ARMv4 based CPUs, but the linker can work around this by rewriting >>> those instructions to the ARMv4 version if we pass --fix-v4bx >>> to the linker. This should work with binutils-2.15 (released >>> May 2004) or higher, and we can probably assume that anyone using >>> gcc-7.x will have a much more recent binutils version as well. >>> >>> However, in order to still allow users of old toolchains to link >>> the kernel, we only pass the option to linkers that support it, >>> based on a $(ld-option ...) call. I'm intentionally passing the >>> flag to all linker versions here regardless of whether it's needed >>> or not, so we can more easily spot any regressions if something >>> goes wrong. >>> >>> For consistency, I'm passing the --fix-v4bx flag for both the >>> vmlinux final link and the individual loadable modules. >>> The module loader code already interprets the R_ARM_V4BX relocations >>> in loadable modules and converts bx instructions into mov even >>> when running on ARMv4T or ARMv5 processors. This is now redundant >>> when we pass --fix-v4bx to the linker for building modules, but >>> I see no harm in leaving the current implementation and doing both. >>> >>> Signed-off-by: Arnd Bergmann <arnd@arndb.de> >>> --- >>> Please test by making the -march=armv4t switch unconditional >>> and see if that results in a working kernel >> >> I did this: >> diff --git a/arch/arm/Makefile b/arch/arm/Makefile >> index 66e46aec0cd0..3944ecd6cd31 100644 >> --- a/arch/arm/Makefile >> +++ b/arch/arm/Makefile >> @@ -81,7 +81,7 @@ arch-$(CONFIG_CPU_32v6K) >> =-D__LINUX_ARM_ARCH__=6 $(call cc-option,-march=armv6k, >> endif >> arch-$(CONFIG_CPU_32v5) =-D__LINUX_ARM_ARCH__=5 $(call >> cc-option,-march=armv5te,-march=armv4t) >> arch-$(CONFIG_CPU_32v4T) =-D__LINUX_ARM_ARCH__=4 -march=armv4t >> -arch-$(CONFIG_CPU_32v4) =-D__LINUX_ARM_ARCH__=4 $(call >> cc-option,-march=armv4,-march=armv4t) >> +arch-$(CONFIG_CPU_32v4) =-D__LINUX_ARM_ARCH__=4 -march=armv4t >> arch-$(CONFIG_CPU_32v3) =-D__LINUX_ARM_ARCH__=3 -march=armv3 >> >> Built and booted on the Gemini platform. >> >> It crashes immediately and goes into the boot loader >> on thos FA-526 based platform. > > Hmm, maybe the decompressor needs the fixup separately. Can you try > something like this completely untested patch on top? > > Arnd > > diff --git a/arch/arm/boot/compressed/Makefile > b/arch/arm/boot/compressed/Makefile > index f0548b6948f1..0e141b2cae98 100644 > --- a/arch/arm/boot/compressed/Makefile > +++ b/arch/arm/boot/compressed/Makefile > @@ -134,6 +134,11 @@ endif > ifeq ($(CONFIG_CPU_ENDIAN_BE8),y) > LDFLAGS_vmlinux += --be8 > endif > + > +ifdef CONFIG_CPU_32v4 > +LDFLAGS_vmlinux += --fix-v4bx > +endif > +
Yes this work! The kernel and userspace comes up.
With this folded in: Tested-by: Linus Walleij <linus.walleij@linaro.org> for FA526
I will try to test it on SA110 (NetWinder) tomorrow.
Yours, Linus Walleij
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