On Tue, 2008-04-08 at 15:25 +0200, Stefan Roese wrote:
On Tuesday 08 April 2008, Joakim Tjernlund wrote:
I first did a new symbol for this but changed it to use _start as I didn't want to introduce yet another symbol. I would hope it is possible to rework 4xx to move the _start symbol to were it belongs? Not having the _start symbol where it should be could bite you some other day too.
I think you got this wrong. _start *is* where it should be, where the execution of the code begins. Where you set the breakpoint in gdb.
Ah, right. I *assumed* that _start was always the first symbol in the text segment too. On 4xx it isn't for some reason, but it should be possible to move it first.
Sidnote: Does execution really begin at _start for 4xx? I still looks like it begin at _start_440 and eventually end up at _start
On 4xx execution always starts at 0xfffffffc (last lword in 32bit address space). This location holds a jump to _start for 405 PPC's and to _start_440 for 440 PPC's. 440 PPC's need some extended initialization (TLB setup etc) and later jump to the 4xx common _start.
OK, then it is like I suspected. What if you rename _start to _common_start. Make _start equal _common_start for 405 and rename _start_440 to _start, i.e make sure that _start is defined where you start executing after the jump.
The "new symbol" you mention corresponds to CFG_MONITOR_BASE, but note that it has no fixed address as it depends where you place your image in flash.
Yes, but the address is not important here, it is the difference _end - _start. I guess we could define a linker symbol too that calculates _end - _start for us and then just do len = _uboot_reloc_size + EXC_OFF_SYS_RESET;
or define a new symbol that is initialised to CFG_MONITOR_BASE or let the linker place it at the beginning of .text, hopefully there is already a name reserved for the symbol although I don't know of such a name. I either case I think one needs to add that symbol to the GOT list in start.S
I'm an linker script dyslexic. So no idea if we can handle this solely in the linker script or if we need a new common symbol in the PPC start.S's.
Both ways should be doable I think. A linker script would probably look something like(pseudo diff below): .text : { + _monitor_base = . ; + PROVIDE (_monitor_base = .); cpu/mpc83xx/start.o (.text)
And then add a GOT_ENTRY(_monitor_base) in start.S