5 May
2008
5 May
'08
1:12 p.m.
On Sun, May 04, 2008 at 08:59:25PM -1000, Tim Newsham wrote:
Simh has a cpu execution history which is already
turned on in our
configuration file, so at any point when youre at the simh prompt
you can "show cpu history" to see the recently executed instructions.
Thanks Tim.
It looks like we are not starting /usr/lib/c0 properly: the CPU never gets
to execute at 040000, and we end up in sysbreak without ever calling it.
I have a CPU history from sysexec at 004250 right up to where it hits a
supposed HALT instruction in sysbreak at 005752, which previously was
CMP R1,SP.
Here's the simh and Unix commands I tried:
./simh.cfg
sim> c
:login: root
# /tmp/a.out # Mount /usr
# chdir /usr/tmp
#
Simulation stopped, PC: 007332 (MOV (SP)+,25310)
sim> break 004250
sim> c
/usr/lib/c0 z.c a b # Run pass c0 on z.c, creating a & b tempfiles
Breakpoint, PC: 004250 (JSR R0,5634)
sim> set CPU HISTORY=0
sim> set CPU HISTORY=100000
sim> continue
HALT instruction, PC: 005754 (BCC 5762)
sim> show CPU HISTORY
I won't include the history here, as it's 49,000 instructions. But if
anybody wants a look at it, let me know.
Thanks,
Warren
You can also use breakpoints to do some tracing, for example:
break 1350;ex r0;go
will break at 1350, in syscall right after it figures out what syscall
number, dump r0, which has the syscall number, and continue, so that
you get a running syscall trace..
The downside to these methods is that they capture the entire operating
system, not just a single userland process... It would be nice if
we could rig the emulator to skip over context switches to other
processes.... Then again, it's probably a lot easier than debugging
with blinking lights and switches...
Warren
I suspect there are some more kernel gotchas left to be found. The
fact that "cc" doesnt work properly could be due to my 0407 patch
but could equally be another kernel typo somewhere. The fact that
init doesnt like running getty on other ttys is also making me suspect
some hidden kernel bugs... During one of my tests with "cc" I saw
it go into panic (probably good to run with a breakpoint on panic,
too! see build/a.out.syms) after syscall got reentered!
Tim Newsham
http://www.thenewsh.com/~newsham/
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