Dear J. William Campbell,
> On 10/2/2010 3:17 AM, Joakim Tjernlund wrote:
>>> Hello Reinhard,
>>>
>>> Reinhard Meyer wrote:
>>>> Dear Albert ARIBAUD,
>>>>>> I try to understand how the relocation process could handle pointers (to
>>>>>> functions or other data) in const or data sections.
>>>>>> Your code cannot know what is data and what is a pointer that needs
>>>>>> adjustment?
>>>>>>
>>>>>> Best Regards,
>>>>>> Reinhard
>>>>> Hi Reinhart,
>>>>>
>>>>> Short answer - the relocation process does not handle pointers inside
>>>>> data structures.
>>>>>
>>>>> And yes, this means the content arrays of pointers such as init_sequence
>>>>> is not relocated. Been there, done that, can give you one of the
>>> The init_sequence should not called anymore after relocation, as it is
>>> the init_sequence ... or?
>>>
>>>>> tee-shirts I got :)
>>>>>
>>>>> ATM I have not found a way to fix this, except making the code which
>>>>> uses the pointers aware that the are location-sensitive and fix them
>>>>> when using them.
>>>> That means that things like this cannot work (with relocation),
>>>> unless adding the relocation offset before using the pointer:
>>> Yep, you have to fix these pointers after relocation ...
>>>
>>>> const struct {
>>>> const u8 shift;
>>>> const u8 idcode;
>>>> struct spi_flash *(*probe) (struct spi_slave *spi, u8 *idcode);
>>>> } flashes[] = {
>>>> #ifdef CONFIG_SPI_FLASH_SPANSION
>>>> { 0, 0x01, spi_flash_probe_spansion, },
>>>> #endif
>>> [...]
>>>> #ifdef CONFIG_SPI_FRAM_RAMTRON
>>>> { 6, 0xc2, spi_fram_probe_ramtron, },
>>>> # ifdef CONFIG_SPI_FRAM_RAMTRON_NON_JEDEC
>>>> { 0, 0xff, spi_fram_probe_ramtron, },
>>>> # endif
>>>> # undef IDBUF_LEN
>>>> # define IDBUF_LEN 9 /* we need to read 6+3 bytes */
>>>> #endif
>>>> };
>>>>
>>>> And I think there are more places of this type in u-boot...
>>> Yes, maybe. But relocation as I did for arm, also works
>>> on m68k, sparc, mips, avr32 and they must do also this
>>> fixups, so for common functions (except the new env handling,
>>> which I think got never tested on this architectures?) should
>>> work ...
>> This pointer problem is solved with the fixup relocs on ppc and
>> should work without manual relocation. I think this is a ppc
>> only extension but I might be wrong.
>
> Hi All,
> You are correct that this is a ppc only extension. As such, it is not a good
> candidate for "general" use.
>
>> I believe that the other alternative is to do it as x86 does
>> which I think is the general way which should work on any arch.
>> Graem Russ would know better.
>>
> Almost exactly a year ago, this was all pretty much presented by Graeme in
> the threads
> Relocation size penalty calculation (October 14, 2009)
> i386 Relocation (November 24, 2009)
>
> Using the full relocation scheme eliminates the need for all these "fixups"
> in u-boot C code. I think this is a very desirable result.
> It is also not clear to me that hard coding in the relocation as several C
> routines will produce a u-boot that is "smaller" than the one produced by
> using normal ELF relocation. However, using full relocation creates an
> environment that is true "C" and does not rely on people remembering that
> they may have to fix up some parts of their code. It is hard to see much
> downside in using the full relocation capability provided by Graeme's code.
> FWIW, the relocation code and data does not have to be moved into ram if
> space is at a premium.
I agree here. _If_ relocation, it should work without hand-adding
fixup stuff to all functions using initialized data with pointers.
Even Wolfgang forgot to fixup his 2nd level command table in
cmd_nvedit.c ;)
And, for space concerns in flash, relocation should always be an
option on a board by board basis...
And as an idea, if position independent code is used, only pointers
in initialized data need adjustment. Cannot the linker emit a table
of addresses that need fixing?
Best Regards,
Reinhard
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