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RE: Use of r31 on the powerpc/booke:mpc85xx architecture
My mistake, the last set of listed registers is in this case a list of
registers implicitly clobbered by the inline assembly. If I understand
correctly this pmap_copy_page() function is incompatible with preservation of
the frame pointer. Perhaps falling back on a non-optimized pmap_copy_page()
when DDB is enabled is the right course of action excepting an alternative
optimized implementation which preserves r31.
[mailto:port-powerpc-owner%NetBSD.org@localhost] On Behalf Of Scislowicz, Adam
Sent: Thursday, September 06, 2012 5:12 PM
Subject: Use of r31 on the powerpc/booke:mpc85xx architecture
In sys/arch/powerpc/booke/booke_pmap.c:pmap_copy_page() The r31 register is
used. When compiling for DDB support with "-fno-omit-frame-pointer" the
compiler complains about the use of register 31. I am new to this architecture
but it seems that register is used as the frame pointer.
If you modify the inline assembly to use r23-r30 instead of r24-r31 it seems to
solve the problem, but I wanted to ask if this is the right way to change this
particular code as I am new to this architecture and don't want to introduce
any unpredictable side effects when making the change locally.
It also seems that DDB support may not be functioning yet on the powerpc/booke
architecture. Is this the known state of things with this port? I am using a
P2020RDB-like system and using the P2020RDB config file which references the
board code in mpc85xx. While the system otherwise works to some extent: I can
boot and use user-space tools when not using DDB. However when I compile with
DDB support I get a trap fairly early in the kernel initialization process and
then my watchdog reboots the system from out of under me.
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