[Crash-utility] [PATCH 0/4] MIPS support

[Dave Anderson]

----- Original Message -----
> On Mon, Jan 12, 2015 at 11:00:08AM -0500, Dave Anderson wrote:
> > I don't know what the real-world usage is with respect to little-endian
> > vs. big-endian 32-bit MIPS, but you got here first.  And in the
> > future, it should be simple enough to support big-endian MIPS as
> > well, i.e., in the same manner that both little- and big-endian PPC64
> > are supported.

FWIW, I see that http://www.linux-mips.org/wiki/Endianess indicates: 

  On 32-bit kernels there seems to be somewhat a majority of big endian systems. 
  Distribution download figures suggset approximately a 60:40 ratio. 

> 
> I attempted to have a quick look at big-endian while making the patch
> (it's easy to emulate big-endian MIPS too on QEMU), and if I understand
> correctly from the PPC handling, the host endianness needs to match the
> target endianness.  So that means we can't analyze big-endian MIPS dumps
> on x86/x86-64 hosts, right?

That's correct.  

> 
> The MIPS systems which I personally plan to use this for are
> little-endian, and the analysis will be done on x86-64 hosts.
> 
> > Running cscope from the gdb-7.6 subdirectory on down shows only
> > this single reference to convert:
> > 
> >   sim/mips/sim-main.h Convert  774 #define Convert(rm,op,from,to) convert
> >   (SIM_ARGS, rm, op, from, to)
> > 
> > But it doesn't show any callers to Convert() or convert().  So
> > it appears to exist as a non-static function in "sim/mips/cp1.c"
> > that nobody calls?  In any case, please make the convert() name
> > change down in the gdb-7.6/sim/mips code, and update gdb-7.6.patch
> > accordingly.
> 
> Done.  Convert() is used in the mips.igen file in the same directory,
> which appears to be used to generate C code and compile it as part of
> the build process.

Ah, of course, cscope didn't check that file.

> 
> > Also in defs.h, please put the task_struct_thread_reg29 and
> > task_struct_thread_reg31 offsets at the end of the offset_table
> > structure.  Again, new entries to that structure should always
> > be appended to the structure so that it won't break the usage
> > of OFFSET() by pre-existing extension modules.  Also, you should
> > add their offset value displays to dump_offset_table() for use
> > by "help -o", and in that function, you can display it next to
> > the other task_struct_thread_xxx offsets.
> 
> Done.
> 
> > On another note, there should be an understandable and clean
> > protection mechanism against running a target=MIPS binary on a
> > live host system.  So when attempting to run a target=ARM crash
> > binary on an x86/x86_64 host, it fails like so:
> > 
> >   $ sudo ./crash
> >   crash: compiled for the ARM architecture
> >   
> > With your target=MIPS binary, it shows this confusing error message:
> >   
> >   crash: cannot resolve "cpu_data"
> >   
> > It's a small check that can be put at the beginning of mips_init().
> > I presume that you used ppc.c as a template, so if you'd like, you
> > can add the same fix there as well.
> 
> ppc.c doesn't have that check, but I've added it to mips.c based on
> what's in arm.c.

Right -- what I meant was that you could make the same fix in ppc.c as well.

> 
> > Lastly (at least at this point), can you update the README[] strings array
> > in help.c to show that MIPS is a supported architecture, and that it can
> > be build as a "target=" binary?
> 
> Done.
> 
> > Oh, and thanks very much for the sample vmcores.  I'll keep them around for future
> > testing.  BTW, the System.map file is completely unnecessary -- is there a reason
> > you included it?
> 
> Not really.  I never used it but thought "just in case" while zipping up
> the dumps + vmlinux.
> 
> Rabin

OK good -- I'll check this new patchset out tomorrow.

Thanks,
  Dave