[Crash-utility] [PATCH] ARM: fix unwinding on recent kernels

[Dave Anderson]

----- Original Message -----
> On Sat, Feb 11, 2012 at 08:00:34PM +0530, Rabin Vincent wrote:
> > Unwinding doesn't work on recent ARM kernels since after the following
> > commit the kernel doesn't perform the prel31_to_addr() conversion of the
> > offsets in the index table.  The leads to crash not finding the correct
> > unwind instructions.
> > 
> > http://git.kernel.org/linus/de66a979012dbc66b1ec0125795a3f79ee667b8a
> > 
> > The patch below makes crash do the conversion itself if necessary.
> > 
> > Rabin
> > 
> > diff --git a/unwind_arm.c b/unwind_arm.c
> > index d86ec63..e804cfb 100644
> > --- a/unwind_arm.c
> > +++ b/unwind_arm.c
> > @@ -71,6 +71,8 @@ struct unwind_table {
> >  static struct unwind_table	*kernel_unwind_table;
> >  static struct unwind_table	*module_unwind_tables;
> >  
> > +static int index_in_prel31;
> > +
> >  struct unwind_ctrl_block {
> >  	ulong	vrs[16];
> >  	ulong	insn;
> > @@ -104,6 +106,7 @@ static int is_core_kernel_text(ulong);
> >  static struct unwind_table *search_table(ulong);
> >  static struct unwind_idx *search_index(const struct unwind_table
> >  *, ulong);
> >  static ulong prel31_to_addr(ulong, ulong);
> > +static void index_prel31_to_addr(struct unwind_table *);
> >  static int unwind_frame(struct stackframe *, ulong);
> >  
> >  /*
> > @@ -187,6 +190,8 @@ init_kernel_unwind_table(void)
> >  		goto fail;
> >  	}
> >  
> > +	index_in_prel31 =
> > !is_kernel_text(kernel_unwind_table->idx[0].addr);
> 
> Maybe add some comment explaining why we do this check (a reference to the
> kernel commit perhaps)?

I agree about the comment -- and then some...

This seems to be a fairly signficant piece of information to be hidden
in a static variable:

+static int index_in_prel31;

Can you put it in the ARM machine_specific data structure?  And then 
display it in arm_dump_machdep_table() for "help -m".

Thanks,
  Dave