Re: [Crash-utility] arm64: "bt -f" output

> 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... ;-)

From the vmlinux/vmcore binaries that I sent you before,

Thanks, Dave -- Crash-utility mailing list Crash-utility(a)redhat.com https://www.redhat.com/mailman/listinfo/crash-utility