On 05.12.18 10:45, David Hildenbrand wrote: > On 04.12.18 14:48, Janosch Frank wrote: >> LPAR and z/VM start in esam mode, so we need to switch to z/Arch and >> set 64 bit addressing. >> >> Under Qemu/KVM we already start out with both when being run with the >> Qemu --kernel argument or we lack only 64 bit when booting from disk. >> >> Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx> >> --- >> s390x/cstart64.S | 9 +++++++++ >> 1 file changed, 9 insertions(+) >> >> diff --git a/s390x/cstart64.S b/s390x/cstart64.S >> index abd6b58..80dbcba 100644 >> --- a/s390x/cstart64.S >> +++ b/s390x/cstart64.S >> @@ -20,6 +20,15 @@ >> */ >> .globl start >> start: >> + tam # Test for 64 bit addressing (KVM IPL) >> + brc 1, start64 # If cc = 3 (64 bit), we have z/Arch > > Looking at the kernel, we don't have to test for 64bit but can simply do > that always unconditionally. SIGP might bail out but we ignore it. sam64 > will also simply do nothing. > > So tam+brc are not necessary. Right, sigp will be a nop with inv parm and inc state as a return. I guess we don't need to save cycles here so I can get rid of the branch. > >> + /* Switch to z/Architecture mode (64-bit) */ >> + slr %r0, %r0 # set cpuid to zero >> + lhi %r1, 2 # mode 2 = esame >> + sigp %r1, %r0, 0x12 # sigp set arch >> + bras %r13,0f >> + .fill 16,4,0x0 >> +0: lmh %r0,%r15,0(%r13) # clear high-order half of gprs > > This is just what the kernel does. The ".fill" part is confusing at > first, but it is just the data loaded into the high-order halfs (all 0s) > > (I was told mixing code and data is bad practice, but for some reason > people in Linux decided to do it like that (maybe because of some > relocation thingy? or because of instruction set restrictions?)) Honestly I wouldn't even have considered clearing if I haven't seen it in the kernel. I could define a zero area at the end of the file or do an lm targeting the cleared bss right before jumping into setup. Or we could do 16 xc register to register :) > > Should we introduce defines for SIGPs? We might have more once we > support multiple CPUs eiher way. We also have sigp stop so why not. How about making the indent patch a cleanup patch and adding all commands there? > >> sam64 # Set addressing mode to 64 bit >> start64: >> /* setup stack */ >> >
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