Re: [Gold] how to do relax in Gold ?

[Ian Lance Taylor <iant at google dot com>]

On Wed, Jan 16, 2013 at 12:24 AM, Shawn <shaolin.xie@ia.ac.cn> wrote:
> On 2013å01æ16æ 14:09, Ian Lance Taylor wrote:
>>
>> On Tue, Jan 15, 2013 at 10:02 PM, Shawn <shaolin.xie@ia.ac.cn> wrote:
>>>
>>> Hi All:
>>>      I'am porting Gold to our processor right now ,everything is fine
>>> except
>>> the label whose value is big.  For Example, the following instruction
>>> assign
>>> a LABEL value to register R0:
>>>     ===========
>>>      R0 = LABEL_0;
>>>     ===========
>>>
>>> 1. Our Objects
>>>    Our instruction is encoded in 32bit,   if the value of "LABLE_0" is
>>> too
>>> big, for example 0x40000, there is not enough space to encode the
>>> instruction into a 32bit instruction, we have to expand "R0 = LABEL_0"
>>> into
>>> a 64bit instruction automatically.
>>>    Because the value of "LABEL_0" is not known until link-time, we hope
>>> "Gold" can handle this .
>>>
>>> 2. My plan  & Question:
>>>    I found the function related to our object is  the "Target::do_relax"
>>> function, but only arm.cc & powerpc.cc has overwritten it. The "do_relax"
>>> in
>>> arm.cc & powerpc.cc is too complicate to analyze. I hope to get a clean
>>> implementation of Our Objects.
>>>     a)  Scan  relocation info in all input objects, find the relocations
>>> that
>>> may  need relaxation ( read & compare the symbol value )
>>>           How can I read the relocation info ?
>>>           How can I reany advice ad the symbol  value ? Is the value read
>>> from the Symbol_table represent the value after layout ?
>>>     b)  for each relocation that  need relaxation, insert a 32bit stub in
>>> the
>>> VIEW, and update the value of the symbol which is located after the
>>> relocation site.
>>>
>>>      And is there any other example related to relaxation except arm.cc &
>>> powerpc.cc ? or any document ?
>>
>> No, sorry.
>>
>> I think one approach would be to record the possible relaxation points
>> in your scan_relocs routine.  You will have all the relocation
>> information available there.  That will let you detect out of range
>> relocations where you can insert stubs.
>>
>> Ian
>>
> Thanks Ian. Did your mean Target::scan_relocs ? I will try that.

Yes.

Ian