[Aboriginal] armv4tl floating exception message in guest
rob at landley.net
Mon Apr 8 10:11:22 PDT 2013
On 04/06/2013 09:37:36 AM, mobi phil wrote:
> > Static strace binaries are in the "extras" directory, you should be
> able to
> > fetch them with wget through the virtual network. They may not have
> > for this release (200k/second times a large number of megabytes,
> and I can't
> > upload from this netbook at woork but only out and lunch and such).
> thanks, was not aware about the extras directory
I need to improve the documentation, but haven't figured out how to do
so without making it so big you can't find anything because of the
All of my attempts to sit down and systematically document this project
turn into giant things like
which isn't what I'm going for. I'm actually pretty happy with how
_short_ I managed to get the recent rewrite of the about.html page.
> > Adding gdb is a perpetual todo item, I think my most recent stab at
> it was
> > somewhere around http://landley.net/notes-2010.html#15-02-2010 but
> mostly I
> > don't use gdb, so I wait for people who do to note its absence.
> you made me curious. can you tell me please what would you have used
> in this particular situation (and restricted environment) to figure
> out where the floating exception is coming from?
We debugged it on this list in December:
What I usually do is recompile the source of the offending command and
stick printf() calls into it until I tracked down the line that was
faulting. (If it didn't print, that was after the segfault, if it did
print it was before.) Then I'd print out the values of the calculation
it was doing and found the division by zero error and trace that data
back to where it came from.
In this case, somebody else ran gdb on it before I got around to
looking at it:
But if you have a build environment set up and can recompile the
program with extra logging of your choice stuck in anywhere, gdb
doesn't buy you all that much. Where gdb shines is when you _can't_
easily do that. Since I'm building this whole system from source...
I sometimes use the -s option of the various qemu variants to hook up
gdb via "target remote":
But that's for stuff I can't stick a printf in. (And I've managed to
stick a printf into the uClibc dynamic linker.) The case above was
debugging the glue tinycc put between _start and main(). I've also had
to debug uclibc and qemu disagreeing about what that init code should
do on powerpc, but gdb wasn't helpful there. (objdump -d was, and I
stuck printf()s in qemu.)
Here's a longish debugging session I did without gdb:
And so on, and so forth. I pull out gdb when I have no other choice,
but that's almost never the case.
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