Re: [PATCH v4 6/6] arm64: ftrace: add arch-specific stack tracer

From: AKASHI Takahiro
Date: Wed Nov 04 2015 - 03:02:13 EST


On 11/01/2015 05:30 PM, Jungseok Lee wrote:
On Oct 30, 2015, at 2:25 PM, AKASHI Takahiro wrote:

Hi Akashi,

Stack tracer on arm64, check_stack(), is uniqeue in the following
* analyze a function prologue of a traced function to estimate a more
accurate stack pointer value, replacing naive '<child's fp> + 0x10.'
* use walk_stackframe(), instead of slurping stack contents as orignal
check_stack() does, to identify a stack frame and a stack index (height)
for every callsite.

Regarding a function prologue analyzer, there is no guarantee that we can
handle all the possible patterns of function prologue as gcc does not use
any fixed templates to generate them. 'Instruction scheduling' is another
issue here.
Nevertheless, the current version will surely cover almost all the cases
in the kernel image and give us useful information on stack pointers.

Can I get an idea on how to test the function prologue analyzer? It pretty
tough to compare stack trace data with objdump one. Is there an easier way
to observe this enhancement without objdump?

It is quite difficult to give an evidence of the correctness of my function
prologue analyzer. I only checked the outputs from stack tracer, one by one
(every function), by comparing it against its disassembled code.

-Takahiro AKASHI

Best Regards
Jungseok Lee

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