[U-Boot] Query on CONFIG_SYS_THUMB_BUILD

Victor Ascroft
2014-11-15T05:38:22Z

On 11/15/2014 10:56 AM, Victor Ascroft wrote:
> On 11/15/2014 07:26 AM, Simon Glass wrote:
>> Hi Albert,
>>
>> On 14 November 2014 08:26, Albert ARIBAUD <albert.u.boot@aribaud.net> wrote:
>>> Hello Simon,
>>>
>>> On Fri, 14 Nov 2014 07:01:59 -0700, Simon Glass <sjg@chromium.org>
>>> wrote:
>>>> Hi Victor,
>>>>
>>>> On 13 November 2014 09:29, Victor Ascroft <victorascroft@gmail.com> wrote:
>>>>> Hello,
>>>>>
>>>>> I am working with a Cortex A5 Freescale Vybrid Processor. Since a thumb build leads to a saving of almost 1 MB for my u-boot image and consequently to faster serial downloads I have been looking at this. Currently enabling this option leads to a hang.
>>>>>
>>>>> After some debugging I have narrowed the place of hang to "ldr pc, =board_init_r" in arch/arm/lib/crt0.S. My debugging procedure was to put a branch to a small function which just printed a small message with puts, just before the ldr instruction and then a printing a small message with puts just at the start of board_init_r in common/board_r.c . For a non thumb build, the two messages get printed and I can boot to the u-boot prompt. For a thumb build, only the first message before the ldr instruction gets printed.
>>>>>
>>>>> In crt0.S
>>>>> bl debug_print
>>>>> ldr pc, =board_init_r
>>>>>
>>>>> In board_init_r
>>>>> puts("In board_init_r\n"); // Right at start
>>>>>
>>>>> void debug_print(void)
>>>>> {
>>>>> // Defined in board file
>>>>> puts("Debug print\n");
>>>>> }
>>>>>
>>>>> My assembly knowledge is limited and after some consultation with a senior colleague, he told me things to check.
>>>>>
>>>>> An object dump of the crt0.o shows a branch to an even address. For thumb, this is expected to be odd. To just try out, I did a change as below
>>>>> ldr r3, =board_init_r
>>>>> add r3, #1
>>>>> bx r3
>>>>>
>>>>> No change with this. My expectation was the compiler/linker/assembler would take care of the requirements, with the CONFIG_SYS_THUMB_BUILD. Frankly speaking I am not sure if this is the complete issue or only a part of it. I have seen patches with regards to OMAP send in by Aneesh V, which made changes of the form .type fn_name, %function to all the low level assembly functions, but, I couldn't dig up much more or variants thereof. Basically, from what I understand, this takes care of specifying .thumb_func for a thumb function or so to speak.
>>>>>
>>>>> Any pointers?
>>>
>>> Victor,
>>>
>>> In addition to Simon's question below on the toolchain, I would like to
>>> know which commit you're trying to build.
>
> I am using u-boot 2014.10, but, I have a modified branch which supports my hardware
> and I also have changes for having USB Host and Client support for the Vybrid platform.
>
> The toolchain I am using is gcc-linaro-arm-linux-gnueabihf-2012.09-20120921
>
> http://www.codesourcery.com/public/gnu_toolchain/arm-none-linux-gnueabi/arm-2009q3-67-arm-none-linux-gnueabi-i686-pc-linux-gnu.tar.bz2

http://launchpad.net/linaro-toolchain-binaries/trunk/2012.09/+download/gcc-linaro-arm-linux-gnueabihf-2012.09-20120921_linux.tar.bz2

Sorry I gave the link for the soft floating one by mistake :(.
>
> I have downloaded it from the above link.
>
>>>
>>>> I tried this on a peach_pi (Samsung Chromebook 2 13") and it worked OK
>>>> for me. The code sequence you refer to came out as below for me.
>>>>
>>>> 23e01e10 <clbss_l>:
>>>> 23e01e10: e1500001 cmp r0, r1
>>>> 23e01e14: 35802000 strcc r2, [r0]
>>>> 23e01e18: 32800004 addcc r0, r0, #4
>>>> 23e01e1c: 3afffffb bcc 23e01e10 <clbss_l>
>>>> 23e01e20: fa000dec blx 23e055d8 <coloured_LED_init>
>>>> 23e01e24: fb000deb blx 23e055da <red_led_on>
>>>> 23e01e28: e1a00009 mov r0, r9
>>>> 23e01e2c: e5991030 ldr r1, [r9, #48] ; 0x30
>>>> 23e01e30: e59ff008 ldr pc, [pc, #8] ; 23e01e40
>>>> <clbss_l+0x30>
>>>> 23e01e34: 02073800 .word 0x02073800
>>>> 23e01e38: 23e41eb0 .word 0x23e41eb0
>>>> 23e01e3c: 23e77bf0 .word 0x23e77bf0
>>>> 23e01e40: 23e057a9 .word 0x23e057a9
>>>>
>>>> The 'ldr pc' line is loading from 23e01e40 which does have an odd address.
>>>>
>>>> What toolchain are you using? I tried with gcc 4.8.2 - including
>>>> linaro's 2013.10 release.
>>>>
>>>> In arch/arm/cpu/armv7/config.mk there is a fallback to armv5 from
>>>> armv7-a, and this may cause it to generate Thumb code instead of Thumb
>>>> 2. But you should get errors if that happens.
>>>>
>>>> It's hard to debug with such limited visibility. But if I put a puts()
>>>> at the start of board_init_r(), I see it on the serial console.
>>>
>>> Simon,
>>>
>>> I believe you've built crt0.S for ARM, not Thumb.
>>
>> Yes, but I suspect that is a function of the build system. I checked
>> the rest of U-Boot and most of it (including SPL) is Thumb 2. I
>> suppose we could use Thumb 2 for crt0.S if all the instructions are
>> supported.
>
> Yes Simon, you had it for ARM. I also believed it is a function of the
> build system. But, does crt0.S have to be in Thumb2? Thumb interop is
> not enough with ARM and Thumb co-existing?
>
> Does CONFIG_SYS_THUMB_BUILD require any specific changes to the build
> system. I was under the impression, the configuration would take care
> of it. I can do any changes are required, but, I have no knowledge of
> it.
>>
>> Regards,
>> Simon
>>
>
> Regards,
> Victor.
>