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From: Bryce <philip.copeland@oracle.com>
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Subject: Question on checking the stack
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Setting up a probe for a function is great and all but is there a way to 
test how we entered the routine?
 eg
  0xc024d991 : generic_make_request+0xa/0x24b
  0xc0145d20 : find_get_page+0x37/0x42
and
 0xc024d991 : generic_make_request+0xa/0x24b
 0xc024dc17 : submit_bio+0x45/0xcb

I'm not interested in  EVERY time we trace into a function, only when 
we've come from a different routine
is there something along the lines of this idea available?

probe kernel.function("generic_make_request") {
    if (stack(1) == "submit_bio" ) { // where stack(1) was the last 
routine  and stack(2) was 2nd last etc
         do_test/display
    }
}