Booting L4Re on the CI20: Panic in sigma0
paul at boddie.org.uk
Sun Jul 16 02:24:03 CEST 2017
On Saturday 15. July 2017 00.11.58 Paul Boddie wrote:
> However, I'm not managing to actually see the example start. I get the
> following output:
> MOE: Hello world
> MOE: found 245048 KByte free memory
> MOE: found RAM from 1000 to 10000000
> MOE: allocated 255 KByte for the page array @0x104d000
> MOE: virtual user address space [0-7fffffff]
> MOE: rom name space cap -> [C:103000]
> BOOTFS: [1100000-1131e5c] [C:105000] l4re
> BOOTFS: [1132000-1164b08] [C:107000] hello
> MOE: cmdline: moe --init=rom/hello
> MOE: Starting: rom/hello
> MOE: loading 'rom/hello'
> Despite inserting a trace statement into the Moe main program after the
> elf_loader.start invocations, I don't see anything else appear. So I guess
> something else manages to go wrong at this point. I suppose I'll have to
> try and track this down.
So, some more slow but steady progress here.
I decided to see where the code was failing by inserting trace statements and
looking at the output. The failure path involved the elf_loader.start
invocation, through the loader machinery...
...invoking the Moe_app_model (init_prog and copy_ds), ultimately calling
Dataspace_util::copy and l4_cache_coherent.
Naturally, l4_cache_coherent on MIPS employs the rdhwr (read hardware
register) instruction that Sarah mentioned, and although there is code to
handle this instruction when accessing the ULR (User Local Register), there
isn't code to handle access to the SYNCI_Step register which describes the
instruction cache line size. As noted previously, the code for "reserved"
instruction handling is here:
So, I've made an attempt to implement this support in the reserved_insn
handler, accessing the appropriate Config register and reading the value,
setting it in the target register. The existing code wasn't too difficult to
follow, and I hope I haven't broken anything by changing it.
Now, it appears that Moe does complete the loading of "hello", but I still
don't see any output from the example. Switching on all debugging gives the
following output from Moe:
MOE: loading 'rom/hello'
MOE: dump of root name space:
icu -> [C:6000] f=2309
jdb -> [C:a000] f=2317
log -> [C:5000] f=2309
mem -> [C:10d000] o=108edc0 f=2829
rom -> [C:103000] o=108dfe0 f=2816
.dirinfo -> [C:109000] o=108ee80 f=2816
hello -> [C:107000] o=108ef00 f=2816
l4re -> [C:105000] o=108ef80 f=2816
sigma0 -> [C:4000] f=2317
But with the --l4re-dbg option set to "all", after this output...
L4Re: load binary 'rom/hello'
L4Re: Start server loop
...I notice this continuously recurring message:
L4Re[svr]: request: tag=0xfffb1026 proto=-5 obj=0x0
So I imagine now that I will need to investigate what this is all about.
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