Question regarding PowerPC routine compilation.
Zhaobin Zhu
zzhu at emc.com
Tue Sep 26 07:33:14 EST 2000
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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