----- Original Message -----
> On Mon, Jun 13, 2016 at 11:30:24AM -0400, Dave Anderson wrote:
> >
> > > Dave,
> > >
> > > On Fri, Jun 10, 2016 at 04:37:42PM -0400, Dave Anderson wrote:
> > > > Hi Takahiro,
> > > >
> > > > To address my concerns about your patch, I added a few additional
> > > > changes and attached
> > > > it to this email. The changes are:
> > > >
> > > > (1) Prevent the stack dump "below" the #0 level. Yes, the stack data
> > > > region is contained within
> > > > the incoming frame parameters, but it's ugly and we really don't
> > > > care to see what's before
> > > > the #0 crash_kexec and crash_save_cpu #0 frames.
> > > > (2) Fill in the missing stack dump at the top of the process stack, up
> > > > to, but not including
> > > > the user-space exception frame.
> > > > (3) Instead of showing the fp of 0 in the top-most frame's stack
> > > > address, fill it in with the
> > > > address of the user-space exception frame.
> > > >
> > > > Note that there is no dump of the stack containing the user-space
> > > > exception frame, but the
> > > > register dump itself should suffice.
> > >
> > > Well, the essential problem with my patch is that the output from "bt -f"
> > > looks like:
> > > #XX ['fp'] 'function' at 'pc' --- (1)
> > > <function's stack dump> --- (2)
> > > but that (1) and (2) are not printed as a single stack frame in the same
> > > iteration of while loop in arm64_back_trace_cmd().
> > > (I hope you understand what I mean :)
> >
> > Actually I prefer your first approach. I find this new one confusing, not
> > to mention unlike any of the other architectures in that the "frame level"
> > #X address value is not contiguous with the stack addresses that get filled
> > in by -f.
>
> Can you please elaborate a bit here about "is not contiguous"?
I mean that the #X [address] is not contiguous with the stack addresses
above and below it. For example:
ffff8003dc103d60: ffff8003dc103dc0 ffff80000028041c
ffff8003dc103d70: 0000000000000000 0000000000000022
ffff8003dc103d80: ffff8003db846b00 ffff8003db846b00
#3 [ffff8003dc103cf0] schedule_hrtimeout_range_clock at ffff8000007786f0
ffff8003dc103d90: ffff8003dc103dc0 ffff80000028052c
ffff8003dc103da0: 0000000000000000 0000000000000022
ffff8003dc103db0: 0000000000000000 0000000000000000
>
> > Taking your picture into account:
> >
> > stack grows to lower addresses.
> > /|\
> > |
> > | |
> > new sp +------+ <---
> > |dyn | |
> > | vars | |
> > new fp +- - - + |
> > |old fp| | a function's stack frame
> > |old lr| |
> > |static| |
> > | vars| |
> > old sp +------+ <---
> > |dyn |
> > | vars |
> > old fp +------+
> > | |
> >
> > Your first patch seemed natural to me because for any "#X" line containing a function
> > name, that function's dynamic variables, the "old fp/old lr" pair, and the function's
> > static variables were dumped below it (i.e., at higher stack addresses).
> >
> >
> > > To be consistent with the out format of x86, the output should be
> > > <function's stack dump>
> > > #XX ['fp'] 'function' at 'pc'
> > >
> > > Unfortunately, this requires that arm64_back_trace_cmd() and other functions should be overhauled.
> > > Please take a look at my next patch though it is uncompleted and still has room for improvement.
> >
> > I don't know what you mean by "consistent with the out format of x86"? With x86_64,
> > each #<level> line is simply the stack address where the function pushed its return
> > address as a result of its making a "callq" to the next function. Any local variables of
> > the calling function would be at the next higher stack addresses:
> >
> > ...
> > #X [stack address] function2 at 'return address'
> > <function2's local variables>
> > #Y [stack address] function1 at 'return address'
> > <functions1's local variables>
> > ...
> >
> > So for digging out local stack variables associated with a function, it's a simple
> > matter of looking "below" it in the "bt -f" output.
>
> That is exactly what I meant by "consistent with x86."
> On x86, the output looks like:
>
> <function2's local variables>
> #X [stack address] function2 at 'return address'
> <functions1's local variables>
> #Y [stack address] function1 at 'return address'
> ...
No, that's not true -- look at my #X and #Y description above -- funcion2's local
variables are at higher stack addresses than the #X "stack entry" address. They
have to be -- the callq that pushes the return address at the #X stack location is
the last stack manipulation that the function does. Expressed otherwise, a function's
local variables are displayed "below" or "underneath" its #X line in the "bt -f"
output.
>
> So users who are familiar with this format may get confused.
> (Or do I misunderstand anything?)
>
> In addition, my previous patch displays
> <function2's local variables>
> #Y [stack address] function1 at 'return address'
> in arm64_print_stackframe_entry(), and it sounds odd to me.
BTW, the order in which it is done is based upon the kernel's dump_backtrace()
function, although I'll grant you that the kernel dump is only interested in
the pc.
>
> But, anyhow, it's up to you.
>
OK! Thanks for giving in... ;-)
Thanks,
Dave
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