[U-Boot] [u-boot-mips] gp init and -pie option

[Michael Cashwell]

Not to hijack this thread, but I've had trouble with recent (2013.01 and perhaps the last 2012) mainline u-boots for Pandaboard when built using recent Codesourcery Lite tools. I've found that arm-2009q1 and arm-2010q1 work but arm-2012.03 and arm-2012.09 do not. SPL works but u-boot hangs very early.

It's on my list of things to look into.

-Michael Cashwell

On Feb 26, 2013, at 1:12 PM, "Juhyun (Justin) Oh" <Juhyun_Oh at sigmadesigns.com> wrote:

> HI Daniel,
> 
> I'm using CodeSourcery 4.5.2. I've configured and have built the code for "incaip" board and "dbau1000". The results are the same. (i.e. gp has been set with wrong value)
> 
> Could you tell me the CodeSourcery toolchain versions known to be working? I'd like to try out the same version.
> 
> Thanks,
> Justin
> 
> ________________________________________
> From: Daniel Schwierzeck [daniel.schwierzeck at gmail.com]
> Sent: Tuesday, February 26, 2013 1:52 AM
> To: Juhyun (Justin) Oh
> Cc: u-boot at lists.denx.de
> Subject: Re: [U-Boot] [u-boot-mips] gp init and -pie option
> 
> 2013/2/25 Juhyun (Justin) Oh <Juhyun_Oh at sigmadesigns.com>:
>> Hi,
>> 
>> I got a problem while I was trying out v2013.01.01 on the u-boot-mips fork repo. It looks like my u-boot binary built with "-pie" linker option doesn't work due to wrong "gp" initialization.
>> 
>> In the "start.S" file, the gp is supposed to be initialized with "_gp" because ra will hold the address of ".word _gp" line. The below is part of "start.S".
>> 
>> ----------------------------
>> ...
>>    /* Initialize $gp */
>>    bal 1f
>>     nop
>>    .word   _gp
>> 1:
>>    lw  gp, 0(ra)
>> ...
>> ----------------------------
>> 
>> Without the -pie option, linker puts the start address of the .got section. However, with -pie option, the ".word _gp" is translated to "nop". The below is disassembled code.
>> 
>> ----------------------------------------------------------------------------
>> 84001490 <reset>:
>> ...
>> 840014b8:   40804800    mtc0    zero,c0_count
>> 840014bc:   40805800    mtc0    zero,c0_compare
>> 840014c0:   04110002    bal 840014cc <reset+0x3c>
>> 840014c4:   00000000    nop
>> 840014c8:   00000000    nop <---------------
>> 840014cc:   8ffc0000    lw  gp,0(ra)
>> 840014d0:   3c1d8440    lui sp,0x8440
>> 840014d4:   8f9982c0    lw  t9,-32064(gp)
>> 840014d8:   03200008    jr  t9
>> 840014dc:   00000000    nop
>> ----------------------------------------------------------------------------
>> 
>> Could anyone tell me what is going on here? Am I missing anything?
>> 
>> Thanks,
>> Justin
> 
> which board and toolchain do you use?
> 
> PIE support has been tested with various toolchains from ELDK,
> CodeSourcery and OpenWRT.
> 
> --
> Best regards,
> Daniel
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