[U-Boot-Users] [PATCH] Off-by-two bug when relocating GOT

[Vlad Lungu]

Thomas Lange wrote:
> Vlad Lungu wrote:
>   
>> Shinya Kuribayashi wrote:
>>     
>>> Vlad Lungu wrote:
>>>   
>>>       
>>>> The first two entries are skipped but the number of relocated entries
>>>> is not adjusted; as a result, the first __u_boot_cmd_* structure is
>>>> smashed and no commands can be issued.
>>>>     
>>>>         
>>> This is a known, long stading, pretty critical, but not fixed problem. See below:
>>>
>>> http://search.gmane.org/search.php?group=gmane.comp.boot-loaders.u-boot&query=mips+got
>>>
>>> I'm going to look closely into this.
>>>   
>>>       
>> The thing I don't get is why skip the top two entries in the first place? Is it because 
>> _gp=ALIGN(16) ? Maybe Robert has a point:
>>
>> http://thread.gmane.org/gmane.comp.boot-loaders.u-boot/25533
>>     
>
> Yes, Roberts patch sent 12/15/06 09:53 worked for me when my command
> table suddenly got corrupted.
>   

That's my case:
                0x00000000bfc1d950                _gp = ALIGN (0x10)
                0x00000000bfc1d94c                __got_start = .

.got            0x00000000bfc1d950      0x500
 *(.got)
 .got           0x00000000bfc1d950      0x500 cpu/mips/start.o
                0x00000000bfc1d950                _GLOBAL_OFFSET_TABLE_
                0x00000000bfc1de50                __got_end = .
                0x00000000bfc1de50                . = .
                0x00000000bfc1de50                __u_boot_cmd_start = .

 The thing is,  num_got_entries=(__got_end - __got_start)>>2 and that's 
0x141 and it should be only 0x140.
That is what triggers the bug. In start.S, lines 353-354, $t4 is loaded 
with $gp+8 and $t2 with 2 and not with 0, so in effect
if I substract 2 from $t3 I'm not relocating the last entry, and with 
Robert's patch I'm not relocating the last two.
One more point: loading  $gp with _GLOBAL_OFFSET_TABLE_ is not a good  
idea, it should be loaded with _gp. The value
is the same at the moment, but it's not guaranteed at all, someone could 
start playing with the link scripts and break this.
> It is still not applied to sources.
>
> Is it rejected/pending/forgotten?
>   
Well, it was not a "proper" patch so it kind of fell trought the cracks, 
probably.
This one is a "proper" patch but it's actually wrong, so please don't 
apply it.

Vlad