Re: [PATCH v2] tracing: Function stack size and its name mismatch in arm64

[Jiping Ma]

On 2019å08æ01æ 17:41, Will Deacon wrote:
> On Thu, Aug 01, 2019 at 04:33:40PM +0800, Jiping Ma wrote:
> > In arm64, the PC of the frame is matched to the last frame function,
> > rather than the function of his frame. For the following example, the
> > stack size of occupy_stack_init function should be 3376, rather than 176.
> >
> > Wrong info:
> > Depth Size Location (16 entries)
> > ----- ---- --------
> > 0) 5400 16 __update_load_avg_se.isra.2+0x28/0x220
> > 1) 5384 96 put_prev_entity+0x250/0x338
> > 2) 5288 80 pick_next_task_fair+0x4c4/0x508
> > 3) 5208 72 __schedule+0x100/0x600
> > 4) 5136 184 preempt_schedule_common+0x28/0x48
> > 5) 4952 32 preempt_schedule+0x28/0x30
> > 6) 4920 16 vprintk_emit+0x170/0x1f8
> > 7) 4904 128 vprintk_default+0x48/0x58
> > 8) 4776 64 vprintk_func+0xf8/0x1c8
> > 9) 4712 112 printk+0x70/0x90
> > 10) 4600 176 occupy_stack_init+0x64/0xc0 [kernel_stack]
> > 11) 4424 3376 do_one_initcall+0x68/0x248
> > 12) 1048 144 do_init_module+0x60/0x1f0
> > 13) 904 48 load_module+0x1d50/0x2340
> > 14) 856 352 sys_finit_module+0xd0/0xe8
> > 15) 504 504 el0_svc_naked+0x30/0x34
> >
> > Correct info:
> > Depth Size Location (18 entries)
> > ----- ---- --------
> > 0) 5464 48 cgroup_rstat_updated+0x20/0x100
> > 1) 5416 32 cgroup_base_stat_cputime_account_end.isra.0+0x30/0x60
> > 2) 5384 32 __cgroup_account_cputime+0x3c/0x48
> > 3) 5352 64 update_curr+0xc4/0x1d0
> > 4) 5288 72 pick_next_task_fair+0x444/0x508
> > 5) 5216 184 __schedule+0x100/0x600
> > 6) 5032 32 preempt_schedule_common+0x28/0x48
> > 7) 5000 16 preempt_schedule+0x28/0x30
> > 8) 4984 128 vprintk_emit+0x170/0x1f8
> > 9) 4856 64 vprintk_default+0x48/0x58
> > 10) 4792 112 vprintk_func+0xf8/0x1c8
> > 11) 4680 176 printk+0x70/0x90
> > 12) 4504 80 func_test+0x7c/0xb8 [kernel_stack]
> > 13) 4424 3376 occupy_stack_init+0x7c/0xc0 [kernel_stack]
> > 14) 1048 144 do_one_initcall+0x68/0x248
> > 15) 904 48 do_init_module+0x60/0x1f0
> > 16) 856 352 load_module+0x1d50/0x2340
> > 17) 504 504 sys_finit_module+0xd0/0xe8
> >
> > Signed-off-by: Jiping Ma <jiping.ma2@xxxxxxxxxxxxx>
> > ---
> >   kernel/trace/trace_stack.c | 28 ++++++++++++++++++++++++++--
> >   1 file changed, 26 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
> > index 5d16f73898db..ed80b95abf06 100644
> > --- a/kernel/trace/trace_stack.c
> > +++ b/kernel/trace/trace_stack.c
> > @@ -40,16 +40,28 @@ static void print_max_stack(void)
> >   
> >   	pr_emerg("        Depth    Size   Location    (%d entries)\n"
> >   			   "        -----    ----   --------\n",
> > +#ifdef CONFIG_ARM64
> > +			   stack_trace_nr_entries - 1);
> > +#else
> >   			   stack_trace_nr_entries);
> Sorry, but I have no idea what the problem is here. All I know is that the
> solution looks highly dubious and I find it very hard to believe that the
> arm64 backtracing code is uniquely special as to deserve being called out
> like this. I suspect there's a bug lurking somewhere, but you really need
> to do a better job of explaining the issue rather than simply providing a
> couple of backtraces with no context.
>
> *Why* does the frame appear to be off-by-one?
Because the PC is LR in ARM64 stack actually. Following is ARM64 stack 
layout. Please refer to the figure 3 in 
http://infocenter.arm.com/help/topic/com.arm.doc.ihi0055b/IHI0055B_aapcs64.pdf
ÂÂÂ ÂÂÂ ÂÂÂ LR
ÂÂÂ ÂÂÂ ÂÂÂ FP
ÂÂÂÂÂÂÂÂÂÂÂ ......
ÂÂÂÂÂÂÂÂÂÂÂ LR
ÂÂÂ ÂÂÂ ÂÂÂ FP
Jiping
> Will