Message ID | 20171220130016.3156090-1-arnd@arndb.de |
---|---|
State | New |
Headers | show |
Series | [RFT] ARM: use --fix-v4bx to allow building ARMv4 with future gcc | expand |
Hi Arnd, On 20 December 2017 at 13:00, 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 $(ld-option ...) call. I'm intentionally passing the > flag to all linker versions here regardless of whether it's needed > or not, so we can more easily spot any regressions if something > goes wrong. > > For consistency, I'm passing the --fix-v4bx flag for both the > vmlinux final link and the individual loadable modules. > The module loader code already interprets the R_ARM_V4BX relocations > in loadable modules and converts bx instructions into mov even > when running on ARMv4T or ARMv5 processors. This is now redundant > when we pass --fix-v4bx to the linker for building modules, but > I see no harm in leaving the current implementation and doing both. > Are you sure --fix-v4bx is taken into account during a partial link? > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > --- > Please test by making the -march=armv4t switch unconditional > and see if that results in a working kernel > > arch/arm/Makefile | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/arch/arm/Makefile b/arch/arm/Makefile > index e83f5161fdd8..33b7eb4502aa 100644 > --- a/arch/arm/Makefile > +++ b/arch/arm/Makefile > @@ -19,6 +19,11 @@ LDFLAGS_vmlinux += --be8 > KBUILD_LDFLAGS_MODULE += --be8 > endif > > +ifeq ($(CONFIG_CPU_32v4),y) > +LDFLAGS_vmlinux += $(call ld-option,--fix-v4bx) > +LDFLAGS_MODULE += $(call ld-option,--fix-v4bx) > +endif > + > ifeq ($(CONFIG_ARM_MODULE_PLTS),y) > KBUILD_LDFLAGS_MODULE += -T $(srctree)/arch/arm/kernel/module.lds > endif > @@ -76,7 +81,7 @@ arch-$(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-$(CONFIG_CPU_32v4) =-D__LINUX_ARM_ARCH__=4 -march=armv4 > +arch-$(CONFIG_CPU_32v4) =-D__LINUX_ARM_ARCH__=4 $(call cc-option,-march=armv4,-march=armv4t) > arch-$(CONFIG_CPU_32v3) =-D__LINUX_ARM_ARCH__=3 -march=armv3 > > # Evaluate arch cc-option calls now > @@ -94,8 +99,8 @@ tune-$(CONFIG_CPU_ARM922T) =-mtune=arm9tdmi > tune-$(CONFIG_CPU_ARM925T) =-mtune=arm9tdmi > tune-$(CONFIG_CPU_ARM926T) =-mtune=arm9tdmi > tune-$(CONFIG_CPU_FA526) =-mtune=arm9tdmi > -tune-$(CONFIG_CPU_SA110) =-mtune=strongarm110 > -tune-$(CONFIG_CPU_SA1100) =-mtune=strongarm1100 > +tune-$(CONFIG_CPU_SA110) =$(call cc-option,-mtune=strongarm110) > +tune-$(CONFIG_CPU_SA1100) =$(call cc-option,-mtune=strongarm1100) > tune-$(CONFIG_CPU_XSCALE) =$(call cc-option,-mtune=xscale,-mtune=strongarm110) -Wa,-mcpu=xscale > tune-$(CONFIG_CPU_XSC3) =$(call cc-option,-mtune=xscale,-mtune=strongarm110) -Wa,-mcpu=xscale Shouldn't these two be updated as well? > tune-$(CONFIG_CPU_FEROCEON) =$(call cc-option,-mtune=marvell-f,-mtune=xscale) > -- > 2.9.0 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Wed, Dec 20, 2017 at 2:46 PM, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: > On 20 December 2017 at 13:00, Arnd Bergmann <arnd@arndb.de> wrote: >> 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. >> > > Are you sure --fix-v4bx is taken into account during a partial link? No. I made the patch a long time ago, so I don't remember what exactly led me to this decision, but it should be fine as long as the linker does the transformation at least once. >> +tune-$(CONFIG_CPU_SA110) =$(call cc-option,-mtune=strongarm110) >> +tune-$(CONFIG_CPU_SA1100) =$(call cc-option,-mtune=strongarm1100) >> tune-$(CONFIG_CPU_XSCALE) =$(call cc-option,-mtune=xscale,-mtune=strongarm110) -Wa,-mcpu=xscale >> tune-$(CONFIG_CPU_XSC3) =$(call cc-option,-mtune=xscale,-mtune=strongarm110) -Wa,-mcpu=xscale > > Shouldn't these two be updated as well? All compilers that drop -mtune=strongarm110 support for now still support mtune=xscale, so I don't think we need to change them. One thing we could consider is passing -mtune=xscale when building for StrongARM, if that produces better code than the default -mtune=arm7tdmi, but from looking at the gcc-8 sources, it's not clear if that's better or worse. Neither arm7tdmi nor strongarm have a custom cost function, but xscale has. The difference between arm7tdmi and strongarm110 tuning is just the maximum number of conditional instructions (5 vs 3). A much bigger impact might be to tune for arm9e when building a kernel for ARM926, no idea why we don't already do that (we do it for arm946, which nobody really uses). Also, gcc has optimizations for many ARMv7-A cores that we could use if we decide to make them known in Kconfig. Arnd
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. Yours, Linus Walleij
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 + # ? LDFLAGS_vmlinux += -p # Report unresolved symbol references
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
diff --git a/arch/arm/Makefile b/arch/arm/Makefile index e83f5161fdd8..33b7eb4502aa 100644 --- a/arch/arm/Makefile +++ b/arch/arm/Makefile @@ -19,6 +19,11 @@ LDFLAGS_vmlinux += --be8 KBUILD_LDFLAGS_MODULE += --be8 endif +ifeq ($(CONFIG_CPU_32v4),y) +LDFLAGS_vmlinux += $(call ld-option,--fix-v4bx) +LDFLAGS_MODULE += $(call ld-option,--fix-v4bx) +endif + ifeq ($(CONFIG_ARM_MODULE_PLTS),y) KBUILD_LDFLAGS_MODULE += -T $(srctree)/arch/arm/kernel/module.lds endif @@ -76,7 +81,7 @@ arch-$(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-$(CONFIG_CPU_32v4) =-D__LINUX_ARM_ARCH__=4 -march=armv4 +arch-$(CONFIG_CPU_32v4) =-D__LINUX_ARM_ARCH__=4 $(call cc-option,-march=armv4,-march=armv4t) arch-$(CONFIG_CPU_32v3) =-D__LINUX_ARM_ARCH__=3 -march=armv3 # Evaluate arch cc-option calls now @@ -94,8 +99,8 @@ tune-$(CONFIG_CPU_ARM922T) =-mtune=arm9tdmi tune-$(CONFIG_CPU_ARM925T) =-mtune=arm9tdmi tune-$(CONFIG_CPU_ARM926T) =-mtune=arm9tdmi tune-$(CONFIG_CPU_FA526) =-mtune=arm9tdmi -tune-$(CONFIG_CPU_SA110) =-mtune=strongarm110 -tune-$(CONFIG_CPU_SA1100) =-mtune=strongarm1100 +tune-$(CONFIG_CPU_SA110) =$(call cc-option,-mtune=strongarm110) +tune-$(CONFIG_CPU_SA1100) =$(call cc-option,-mtune=strongarm1100) tune-$(CONFIG_CPU_XSCALE) =$(call cc-option,-mtune=xscale,-mtune=strongarm110) -Wa,-mcpu=xscale tune-$(CONFIG_CPU_XSC3) =$(call cc-option,-mtune=xscale,-mtune=strongarm110) -Wa,-mcpu=xscale tune-$(CONFIG_CPU_FEROCEON) =$(call cc-option,-mtune=marvell-f,-mtune=xscale)
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 arch/arm/Makefile | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) -- 2.9.0