[PATCH] ARM: move __fixup_smp out of init section

[Rob Herring]

On Tue, Feb 25, 2014 at 3:10 PM, Arnd Bergmann <arnd at arndb.de> wrote:
> On Tuesday 25 February 2014 15:05:01 Rob Herring wrote:
>> On Tue, Feb 25, 2014 at 12:32 PM, Arnd Bergmann <arnd at arndb.de> wrote:
>> > On Tuesday 25 February 2014 12:16:33 Rob Herring wrote:
>> >> From: Rob Herring <robh at kernel.org>
>> >>
>> >> With large kernel builds such as allyesconfig exceeding maximum relative
>> >> branch offsets, the init section will be too far away to branch to
>> >> directly. This causes veneers to be added by the compiler, but veneers
>> >> don't work before the MMU is enabled. Fix this by moving __fixup_smp to
>> >> the .head.text section as it is not very big.
>> >>
>> >> Signed-off-by: Rob Herring <robh at kernel.org>
>> >
>> > This looks good to me, but I have some related questions:
>> >
>> > * I needed to use -mlong-calls for large kernels. Did you manage without?
>>
>> Yes, but I started with allyesconfig and then disabled things until it
>> would link. This was mainly PCI, various debug, and filesystems. This
>> particular failure you don't see until you try to boot.
>>
>> I also saw intermittent inconsistent kallsym errors which
>> KALLSYMS_EXTRA_PASS=1 did not fix.
>
> Yes, I saw those too. With XIP_KERNEL enabled, I've seen a randconfig case
> that needed 12 extra passes before converging. Without that option,
> it's much better but there are still cases that need more than 3 passes
> and I haven't gotten to the bottom of that. It seems to be the same
> configuration that refuses to link at all with ld.gold.
>
>> > * Do you (or anyone) know how to force the use of a veneer? I see a problem
>> >   with some driver calling __do_div_asm from IIRC an init section, and that
>> >   creates a link error when the kernel gets too big
>>
>> That is surprising given that I saw veneers be inserted for some asm
>> to asm calls. Maybe it is something I turned off or something to do
>> with the types of sections.
>>
>> > * If FUNCTION_TRACER is enabled, we get calls from every function using
>> >  'bl __gnu_mcount_nc'. Do you think it's possible to fix those?
>>
>> Put it in the middle of the image? ;)
>>
>> > * Same thing but simpler for svc_preempt calling preempt_schedule_irq
>> >   and lookup_processor_type calling __lookup_processor_type. In those
>> >   cases I guess we should be able to trivially rewrite the assembly
>> >   to jump through an extra register.
>>
>> I did see that lookup_processor_type had a veneer in my build.
>
> Strange. Could it be that -mlong-calls turns off veneers?
>
> Which gcc and binutils version do you use?

It's the arm cross compiler in ubuntu 13.10:

$ arm-linux-gnueabihf-ld -v
GNU ld (GNU Binutils for Ubuntu) 2.23.52.20130913
$ arm-linux-gnueabihf-gcc -v
Using built-in specs.
COLLECT_GCC=arm-linux-gnueabihf-gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc-cross/arm-linux-gnueabihf/4.8/lto-wrapper
Target: arm-linux-gnueabihf
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.8.1-10ubuntu7'
--with-bugurl=file:///usr/share/doc/gcc-4.8/README.Bugs
--enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.8 --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix
--with-gxx-include-dir=/usr/arm-linux-gnueabihf/include/c++/4.8.1
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--enable-gnu-unique-object --disable-libitm --disable-libquadmath
--enable-plugin --with-system-zlib --disable-browser-plugin
--enable-java-awt=gtk --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.8-armhf-cross/jre
--enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.8-armhf-cross
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.8-armhf-cross
--with-arch-directory=arm
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libgcj
--enable-objc-gc --enable-multiarch --enable-multilib
--disable-sjlj-exceptions --with-arch=armv7-a --with-fpu=vfpv3-d16
--with-float=hard --with-mode=thumb --disable-werror
--enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=arm-linux-gnueabihf
--program-prefix=arm-linux-gnueabihf-
--includedir=/usr/arm-linux-gnueabihf/include
Thread model: posix
gcc version 4.8.1 (Ubuntu/Linaro 4.8.1-10ubuntu7)

Rob