On 03/10/10 18:10, Albert ARIBAUD wrote:
Le 03/10/2010 01:07, Graeme Russ a écrit :
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.
Bill just said that -pic (or, for ARM, -fPIC or -fPIE) was unnecessary for relocation. You seem to imply it actually is... In my experience, -fPIC and-fPIE do increase code by adding GOT relocation to symbols that need fixing, so they would indeed be redundant to any other relocation mechanism -- I just did some test with basic code and this seems to confirm, no -fPIx is needed to get relocation the way you do on ARM.
Just to clarify -fpic is a compiler option, -pic is a linker option. x86 has no compile time relocation options (therefore no referencing .got etc). Using the link time pic option produces the relocation data table (.rel.dyn) which must be pre-processed before execution can begin at the relocated address
Cheers,
Graeme