[Buildroot] libgcc erroneously built as armv5 for arm920t(armv4t)

[Thomas Petazzoni]

Adam,

On Thu, 21 Nov 2013 06:56:10 -0800 (PST), adam hussein\(!\) wrote:

> Sorry for going quiet for so long; a lot of change going on here.

No problem.

> I'm
>  not in a position to work on this board now, the project taking a 
> different direction altogether; however, I have found time for a
> sneaky test of the patch using the internal toolchain, and it seems
> fine.
> 
> The objdump showing that udivsi3 no longer has CLZ instructions.
> 
> arm-buildroot-linux-uclibcgnueabi-objdump -d u-boot | grep
> "20126c1c:" -A 10 20126c1c:    e2512001     subs    r2, r1, #1
> 20126c20:    012fff1e     bxeq    lr
> 20126c24:    3a000036     bcc    20126d04 <__udivsi3+0xe8>
> 20126c28:    e1500001     cmp    r0, r1
> 20126c2c:    9a000022     bls    20126cbc <__udivsi3+0xa0>
> 20126c30:    e1110002     tst    r1, r2
> 20126c34:    0a000023     beq    20126cc8 <__udivsi3+0xac>
> 20126c38:    e311020e     tst    r1, #-536870912    ; 0xe0000000
> 20126c3c:    01a01181     lsleq    r1, r1, #3
> 20126c40:    03a03008     moveq    r3, #8
> 20126c44:    13a03001     movne    r3, #1

Ok, so that's with a Buildroot internal toolchain. Can you also try to
build the kernel with this toolchain to see if it's affected or not by
the below problem?

> Selecting Sourcery CodeBench 2013.05 external toolchain had the
> buildroot make attempt end with:
> 
>   LD      vmlinux
>   SYSMAP  System.map
>   SYSMAP  .tmp_System.map
>   OBJCOPY arch/arm/boot/Image
>   Kernel: arch/arm/boot/Image is ready
>   AS      arch/arm/boot/compressed/head.o
> arch/arm/boot/compressed/head.S: Assembler messages:
> arch/arm/boot/compressed/head.S:936: Error: selected processor does
> not support ARM mode `clz r5,r4'

Ok. I think this is a kernel bug actually. The head.S file is special
in that it contains instructions for ARMv5+, which an ARMv4t assembler
will not accept. But it should, because the code guarantees that the
ARMv5+ instructions will not be executed on ARMv4.

In order to ask the assembler to accept these instructions, the
following commit was made back in 2008:

  http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/arch/arm/boot/compressed/Makefile?id=80cec14a83ad0ad109d822b3f3482a379bc481ba

However, it was reverted recently:

  http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/arch/arm/boot/compressed/Makefile?id=da94a829305f1c217cfdf6771cb1faca0917e3b9

I am not sure how this last commit doesn't break your situation.

It would be interesting if you could confirm whether the kernel builds
or not with the Buildroot internal toolchain.

> And using it for u-boot gave me:
> 
> arm-none-linux-gnueabi-objdump -d u-boot | grep "20126bc0:" -A 10
> 20126bc0:    e2512001     subs    r2, r1, #1
> 20126bc4:    012fff1e     bxeq    lr
> 20126bc8:    3a000074     bcc    20126da0 <__udivsi3+0x1e0>
> 20126bcc:    e1500001     cmp    r0, r1
> 20126bd0:    9a00006b     bls    20126d84 <__udivsi3+0x1c4>
> 20126bd4:    e1110002     tst    r1, r2
> 20126bd8:    0a00006c     beq    20126d90 <__udivsi3+0x1d0>
> 20126bdc:    e16f3f10     clz    r3, r0
> 20126be0:    e16f2f11     clz    r2, r1

So in other words, you mean that this wouldn't work on the target
platform. Hum, weird. Is this a part of U-Boot implemented in assembly,
or something compiled from C ?

Can you give me the relevant informations to allow me to build the
kernel image and U-Boot image myself? Kernel version and configuration
file, U-Boot version and configuration, etc.

Thanks!

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com