On 03/10/10 08:09, Albert ARIBAUD wrote:
Le 02/10/2010 22:39, Reinhard Meyer a écrit :
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?
IIU Bill C, yes the linker can emit the information and the startup code could use this information instead of relying on hand-provided info; the linker file probably needs to be modified in order to provide such info. I intend to look into this, but feel free to do too.
As mentioned previously, I have already done this for x86. The linker flags used are -pic and --emit-relocs. The linker produces a section named rel.dyn which needs to be processed but not loaded into RAM. rel.dyn contains a simple list of address (within .text, .data, .rodata etc) each of which need a simple adjustment equal to the relocation offset.
The size increase of the code + data loaded into RAM is 104012 bytes to 104296 bytes which is only 284 bytes or a mere 0.3% (which is negligible) with an additional 22424 bytes in rel.dyn (22%) not loaded into RAM
The additional bonus is that .got is not referenced during run-time, so there is no run-time performance penalty. However, the penalty of processing 2803 relocation records at startup may not be wholly recovered during a typical u-boot run-time session.
All this is for x86, and may not apply so neatly to other arches
Regards,
Graeme