[U-Boot-Users] Relocation of symbols?
andreas.block at esd-electronics.com
Tue Jun 28 14:50:08 CEST 2005
thanks for your quick reply.
27.06.2005 15:40:25, Wolfgang Denk <wd at denx.de> wrote:
>It's just that not many people really understand all the details how
>the relocation works.
>> The u-boot boots from flash and relocates itself into RAM. After relocation the
>> array is relocated into RAM and so is its content (the pointers to strings). But the
>> actual strings are still located in flash. "walter" is a global symbol located in
>> ".data" section of the compiled object. Is this the behaviour I should expect, or is
>> it a problem with u-boots relocation code?
>If you look at the code, then you will find that the same thing
>happens to all pointers with static initialization. If you think a
>bit about it you will probably be not surprised - how should the
>compiler know that the addresses of your strings might change? and
>after the compiler generated code with a static initializer - who
>should then know that the contents of this variable might need to be
>See for example how we manually adjust (= relocate) the command table
>and other pointer constants in board_init_r().
>I guess you can probably tell GCC to add GOT entries for these
>pointers, but I have to admit that I don't know off-hand what's the
>most efficient way.
I'm not quite sure, if I understood you.
Just to summerize:
1. Absolute symbols are always relocated (my mail: "Does u-boot relocate absolute
2. Statically initialized pointers are never relocated.
I do understand the second point (and can live with this behaviour), but I'd like to
know, where you loose the required information to relocate the pointers as well.
The first point is more important to me. As I understand, absolute symbols shouldn't be
relocated at all. But I guess, you've a similar reason as for the statically
initialized pointers. Anyway: Is it possible in any way to locate the array at the
position I want it to be? Or the other way round: Is it as difficult to prevent
absolute symbols from being added to the GOT as adding something?
>Software Engineering: Embedded and Realtime Systems, Embedded Linux
>Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
>He had quite a powerful intellect, but it was as powerful like a
>locomotive, and ran on rails and was therefore almost impossible to
>steer. - Terry Pratchett, _Lords and Ladies_
More information about the U-Boot