Hi All,
I am trying to fully relocate U-Boot out of the Boot Flash into RAM on my i386 (AMD sc520) board in order to allow the Boot Flash to be flashed from within U-Boot itself (upgrade in place)
I have added code to patch the command table so all the code can be relocated. Further investigation revealed that the code has absolute references into the Boot Flash - printf() format strings are a prime example, but I'm sure there are others
After a bit of searching around the 'net I discovered gcc's -fpie and ld's -pie flags which generation a Position Independent Executable.
This looks like it will do the trick - .text is (practically) identical for varying values of TEXT_BASE and ld produces a .got section as expected. However, ld creates a lot more sections than just .got
Before I go down the path of dissecting all this new and wonderful information, I thought I would quickly ask:
- Am I looking at the problem the wrong way? - Has anyone here looked into making U-Boot 100% relocatable before? - Is U-Boot already 100% relocatable (not just code) for any other platforms? - Has anyone here used pie before and had to write code to adjust the offset tables? - Does anyone know of a good reference for pie / .got / elf (I have found bits and pieces here and there, but no definitive reference)
And lastly - Is it worth the effort, or I should I just set TEXT_BASE to a known memory location and not bother with the relocation at all?
tia
Graeme