Messages in this thread | | | Date | Sat, 3 Nov 2018 13:33:29 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH v3 1/2] kretprobe: produce sane stack traces |
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On Sat, 3 Nov 2018 13:30:21 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:
> What I was thinking was to store a count and the functions to be called: > > > [original_return_address] > [function_A] > [function_B] > [function_C] > [ 3 ] > > Then the trampoline that processes the return codes for ftrace (and > kretprobes and everyone else) can simply do: > > count = pop_shadow_stack(); > for (i = 0; i < count; i++) { > func = pop_shadow_stack(); > func(...); > } > return_address = pop_shadow_stack(); > > That way we only need to register a function to the return handler and > it will be called, without worrying about making trampolines. There > will just be a single trampoline that handles all the work.
And since the most common case is a single function to call, instead of using a count, we can take advantage that kernel functions are negative numbers and do:
[original_return_address] [function_A]
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long count;
count = pop_shadow_stack(); if (count < 0) { func = (void *)count; func(); } else { for (i = 0; i < count; i++) { [...]
The unwinder will just need to know how to handle all this :-)
-- Steve
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