On Tue, Jul 12, 2022 at 4:18 AM Li Huafei [off-list ref] wrote:

When using the frame pointer unwinder, it was found that the stack trace
output of stack_trace_save() is incomplete if the stack contains
call_with_stack():

 [0x7f00002c] dump_stack_task+0x2c/0x90 [hrtimer]
 [0x7f0000a0] hrtimer_hander+0x10/0x18 [hrtimer]
 [0x801a67f0] __hrtimer_run_queues+0x1b0/0x3b4
 [0x801a7350] hrtimer_run_queues+0xc4/0xd8
 [0x801a597c] update_process_times+0x3c/0x88
 [0x801b5a98] tick_periodic+0x50/0xd8
 [0x801b5bf4] tick_handle_periodic+0x24/0x84
 [0x8010ffc4] twd_handler+0x38/0x48
 [0x8017d220] handle_percpu_devid_irq+0xa8/0x244
 [0x80176e9c] generic_handle_domain_irq+0x2c/0x3c
 [0x8052e3a8] gic_handle_irq+0x7c/0x90
 [0x808ab15c] generic_handle_arch_irq+0x60/0x80
 [0x8051191c] call_with_stack+0x1c/0x20

For the frame pointer unwinder, unwind_frame() checks stackframe::fp by
stackframe::sp. Since call_with_stack() switches the SP from one stack
to another, stackframe::fp and stackframe: :sp will point to different
stacks, so we can no longer check stackframe::fp by stackframe::sp. Skip
checking stackframe::fp at this point to avoid this problem.

Signed-off-by: Li Huafei <redacted>

Very nice catch! Took me some time to realize what was
going on here.

Reviewed-by: Linus Walleij <redacted>

Nitpick below:

+       /*
+        * call_with_stack() is the only place we allow SP to jump from one
+        * stack to another, with FP and SP pointing to different stacks,
+        * skipping the FP boundary check at this point.
+        */
+       if (pc >= (unsigned long)&call_with_stack &&
+                       pc < (unsigned long)&call_with_stack_end)
+               return 0;

Can we create a local helper macro to do this, if it needs to happen
some other time?

#define ARM_PC_IN_FUNCTION(pc, func) (pc >=. ...)

Yours,
Linus Walleij

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