"J. William Campbell" jwilliamcampbell@comcast.net wrote on 2010/10/04 19:59:47:
On 10/4/2010 10:06 AM, Wolfgang Denk wrote: Dear "J. William Campbell",
In message 4CA9F294.8080007@comcast.net you wrote:
Yes, I think Wolfgang is correct. This is not going to be easy to do in general. To run anywhere, the code must be true Position Independent code. If you intend to use any C code in the initialization, this will result in needing -fPIC for at least that code. I am not sure you can mix -fPIC and non -fPIC code in the same link, but I expect not. I am a bit surprised that it is possible to get even the initialization code to be Position Independent, but it appears that on at least some PPC it is possible/has been done.
Not really. On PowerPC, only the first 20 or 30 lines of assembler code in start.S are position independent; then we compute the link (resp. execution) address and branch to it. From then, we run from the very address range we were linked for (starting at TEXT_BASE).
Hi Wolfgang, You are of course correct. I was referring more to Jocke's ( joakim.tjernlund@transmode.se) statements regarding: Yes, that is there today. I am talking about linking to any TEXT_BASE(say 0) but burn and run into another address. I impl. this quite some time ago for PPC(search for LINK_OFF)
I understand from his comment that he had achieved total PIC for theinitialization, that would run at any location regardless of TEXT_BASE. I think this code was not accepted into mainline, so it is not a problem at present. However, any relocation code added would have to be modified by Jocke if he wished to preserve that capability. I am amazed that he was able to get the rest of u-boot to work under the constraints you pointed out. It must have been quite tedious.
:), actually it wasn't that bad. Wolfgang nearly accepted the code even :) Mainly, I had to wrap code that accessed global data with a LINK_OFF() function that calculated the offset and only in code that executed before relocation. And fix a few things in start.S to be PIC.
Jocke