On 14-06-10 11:13 AM, Wolfgang Denk wrote:
Dear Steve,
In message <539746c4.9040...@broadcom.com> you wrote:
There could be "many" reasons why the CONFIG_SYS_TEXT_BASE is not
aligned on a 0x1000 byte boundary (Darwin has attempted to document his
particular use-case...)
We should be more precise here and ask for any _good_ reasons.
I can think of many good reasons to keep the text base aligned. As
for the reasons to use an unaligned address that were brought up here,
I still think that it would have been better to use an aligned taxe
base and do the rest with a customized linker script.
But we think that the solution to support this is relatively
straightforward:
(1) after determining the "relocation address" (which will be on a
0x1000 byte boundary),
(2) add "CONFIG_SYS_TEXT_BASE % 4096" to that "relocation address"
(which effectively makes the "relocation offset" a multiple of 0x1000
too...)
So, in the scenario #1, (CONFIG_SYS_TEXT_BASE % 4096) = 0, so this
algorithm changes nothing.
And in scenario #2, (CONFIG_SYS_TEXT_BASE % 4096) = 0x20, therefore, we
would now get the following:
the relocation offset is: 0x77f9b000
therefore, after relocation:
_start symbol is at 0xfff9b020 (0x88000020+0x77f9b000)
vectors symbol is at 0xfff9b800 (0x88000800+0x77f9b000)
I still cannot understand why _start and CONFIG_SYS_TEXT_BASE would
have to be the same. There is no such requirement. What exactly
prevents you from assigning _start a location at offset 0x20 to the
start of the text segment, i. e. CONFIG_SYS_TEXT_BASE ?
Wolfgang et al.
I agree that they do not need to be the same...
So our issue is that basically "for every ARMv7 board in the company",
we are currently maintaining our own modified/customized version of
"arch/arm/cpu/armv7/start.S" in order to add the appropriate 32 byte
header...
And we could choose to do it using other methods, but they all require
us to maintain a customized version of linker scripts, or some other
code, or ....
The request here is that with the addition of some relatively
straightforward (upstreamed) code, then this can be handled
automatically by a post-processing step and we would be able to use a
pristine version of the upstreamed code...
Our desire is to get this into the beginnings of the "ARMv8" boards, so
that we can avoid the maintenance issues we have with the current ARMv7
boards.
We appreciate your consideration of this request.
Thanks, Steve
Then everything should be still the same for you, and no voodoo coding
would be needed.
(3) HOWEVER, shifting the address UP may cause the end of the relocated
code to run past the end of the available memory... So we could:
This problem is void if you just use a poperly aligned text base in
combination with a prope start.S resp. linker script to make sure
_start is where you want it.
I trust that everyone will find this explanation acceptable...
No, I do not see a good reason to add such code.
Best regards,
Wolfgang Denk
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