wolfgang@leila.ping.de (Wolfgang Wegner) wrote on 29/10/2009 16:44:55:
Hi,
although I have to leave for now, just some questions to see if there is anything I understood correctly until now...
- in the PPC startup (assembly) files, the section .got2 is explicitely created using START_GOT etc.
It adds a few entries to .got2 as the asm needs to access a few entries vis the GOT. If you look at the asm generated by gcc, it does the same for global data.
- .got2 contains some vital pointers (vectors) as well as data pointers like a pointer to .fixup and a pointer to itself (?!)
The first entry in got2 host a pointer to itself, this is needed by relocation later. .fixup entries is created by -mrelocatable and WD has mentioned what these are for.
- the ppc linker automatically puts .data.rel (and other relocatable sections?) into .fixup (which seems not the case with my m68k linker)
- the ppc startup code uses some obfuscated assembly code ;-) to relocate both the global relocation table (.got) as well as the sections .got2 and .fixup (.got seems to be implicitly mentioned: "/* First our own GOT */ add r14, r14, r15 /* then the one used by the C code */ add r30, r30, r15" but I can not see where it is actually relocated...)
As I recall that code is a leftover, at least the C version. Relocation happens directly after the in_ram: label. However, this is not you problem. You don't have any relocation entries so there is nothing to relocate. Your linker/linker script is broken.
Is this correct so far? I am not sure because it seems more complicated than necessary to me (especially the algorithm to relocate .got2 and .fixup - or is this all about the possibility to do multiple relocations?), so maybe I still have a misunderstanding here. Furthermore, the special handling of r14 (-ffixed-r14 in config.mk) still puzzles me.
The -ffixed-r14 is for IRQ procressing. The irq code needs to jump to transfer_to_handler via the GOT and needs r14 to hold a ptr to the GOT at all times. This can be avoided and I have a patch to get rid of ffixed-r14 but only for mpc83xx so I or someone else needs to do the other boards too before it can be committed.
Jocke