Question regarding PowerPC routine compilation.

[Jerry Van Baren]

Some registers are protected, some are free game.  For details, see the
ABI (Application Binary Interface) page 3-14 and EABI (Embedded
Application Binary Interface) specifications:
   http://www.esofta.com/softspecs.html

gvb


At 04:33 PM 9/25/00 -0400, Zhaobin Zhu wrote:

>Hi,
>
>This is a newbie question regarding (PowerPC) calling a C routine
>within a .S
>file:
>
>Let me take an example:
>
>in arch/ppc/kernel/head.S,
>...
>         mr      r3,r31
>         mr      r4,r30
>         mr      r5,r29
>         mr      r6,r28
>         mr      r7,r27
>         bl      identify_machine
>...
>The code calls rountine identify_machine(..) in setup.c.
>
>Questions:
>
>    The identify_machine(..) in setup.c will certainly use some of the
> registers
>(r0-r31).
>    Will the compiler protect the registers used in the routine (for
> example
>    push them into stack before entering the routine and pop them out
>    after exiting the routine ) ?
>
>    If yes, how the compiler does the protection ? Will it simply save
> all the
>regs
>    into stack before entering routine and restore them after
> returning from the
>
>    routine (except R3 wiich may be used as a pointer to some returned
> value).
>
>    If compiler does no reg protection, then there is no gurantee that the
>register set
>    will be the same before and after calling a C routine. It's the
> calling
>code's
>    responsibility to make sure some important regs will not be
> altered after
>return
>    from a C routine.
>
>Thanks,
>
>--
>  Zhaobin Zhu
>  zzhu at emc.com
>
>


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