On Sun, Dec 22, 2024 at 10:09:14PM +0100, Arnd Bergmann wrote:

On Sun, Dec 22, 2024, at 03:13, A. Wilcox wrote:

quoted

On Dec 21, 2024, at 3:42 PM, Arnd Bergmann [off-list ref] wrote:

    R0 .. R7           R8 .. R15         R16 .. R23         R24 .. R31
00000000014a1124   0000000000000000   000000000135b4ac   0000000000000000   
000000000dc70f30   ffffffffc0000000   000000000dc70fa4   000000000173600c   
0000000000000000   000000000e477010   0000000000000000   0000000000400000   
ffffffff0141be4c   000000000149ab74   00000000ffffffff   0000000000000008   
00000000c0014b6c   0000000020000402   0000000040400000   00000000016f2000   
ffffffff40400000   0000000000000000   0000000000000000   000000000dc70f60   
0000000000000000   0000000000000000   000000000e73d490   000000000149f000   
0000000000000000   000000000e756118   000000000dc70fa0   ffffffff40400000   

    CR / XER           LR / CTR          SRR0 / SRR1        DAR / DSISR
        80000402   00000000014a1124   00000000014a1128   ffffffff0141be4c   
0000000020040000   0000000000000000   8000000000003000           00000000   


2 > 

Which is the same thing that happens if you boot a 32-bit Linux kernel
on a physical 64-bit Power machine.  This is probably because KVM is
so much more accurate than TCG for Power emulation :)

Did you ask kvm to emulate a 32-bit platform though? Since the
register dump shows 64-bit registers, my guess is that this is the
result of trying to load a 32-bit kernel on "-machine pseries
-cpu native", which is not supported by the guest kernel. I would
expect that you need at least a 32-bit machine type (mac99,
pegasos2) and likely also a 32-bit CPU (7447a, e600).

SLOF always shows 64-bit registers; SLOF only ever runs as 64-bit
program.  The *client* program can be 32-bit of course, but the dump
of SRR1 here shows SF=1 (the top bit there).  No idea what was running
at the time, but something in the kernel I guess?

(To show the last set client state, use
  ciregs .regs
the thing exceptions print is via
  eregs .regs
so you'll probably figure out the format ;-) )

If the client program is a 32-bit ELF file, SLOF starts the client
program with SF=0.


Segher