bootstrap stuffs

Benjamin Herrenschmidt bh40 at
Mon Feb 15 01:02:35 EST 1999

On Sat, Feb 13, 1999, David Edelsohn <dje at> wrote:

Thanks for your reply !

>	Just to make sure, you are not asking how to create XCOFF
>TOC-based code using GCC?

Not really, I already have CodeWarrior and MrC for that ;-)

>	If you know the physical location or can cotrol the physical
>location at which the code will be loaded, you simply can instruct the
>linker to link the executable based at that location.  Otherwise, you
>might need additional -fpic position independent code option.  If you need
>data and cannot set the GPR specifying the GOT address yourself, you can
>use the GCC SVR4 eABI PPC suppport to calculate it on entry as it does for
>embedded systems.  Note that branches generated by GCC already are
>position-independent displacements (not "ba" branch absolute instruction).

I don't know the physical location. The experiments I did yesterday with
various options showed me that the generated branches are bl's except in
some case (the linker-generated branches between .o files were sometimes
ba, but I probably missed an ld option).

So if I understand correctly, I must use -fpic to generate position
independant code. I beleive I must also indicate that this is static code
(no dynamic link). The GOT is a TOC-like register that's it ? I could
probably put a correct value in it if I knew how to find it from the
loader. Do you know which options I should use for CFLAGS and LDFLAGS to
get the result you mentioned ? (GOT calculated on entry).

>	Are all of those "sync" instructions necessary in your code?

Just paranoid. They were added around the interrupt switching to make
sure to sync an eventual second processor and everything else before
switching the MMU off. I beleive that for disabling the MMU, andi. is
probably more efficient than my ori/andc pair, could you just explain my
why you added &0xffff at it ?

>You are not touching memory.  The instructions already are serializing.  I
>think that you should be able to do something like:
>        mfmsr   r0
>        ori     r0,r0,MSR_EE
>        mtmsr   r0
>        mfmsr   r0
>        andi.   r0,r0,(~MSR_EE)&0xffff
>        mtmsr   r0

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