9.29.6 Profiling Capability

It is a performance hit to use gcc's profiling approach for this tiny target. Even more – jtag hardware facility does not perform any profiling functions. However we've got gdb's built-in simulator where we can do anything.

We define new section `.profiler' which holds all profiling information. We define new pseudo operation `.profiler' which will instruct assembler to add new profile entry to the object file. Profile should take place at the present address.

Pseudo operation format:

`.profiler flags,function_to_profile [, cycle_corrector, extra]'

where:

`flags' is a combination of the following characters:

s

function entry

x

function exit

i

function is in init section

f

function is in fini section

l

library call

c

libc standard call

d

stack value demand

I

interrupt service routine

P

prologue start

p

prologue end

E

epilogue start

e

epilogue end

j

long jump / sjlj unwind

a

an arbitrary code fragment

t

extra parameter saved (a constant value like frame size)

function_to_profile

a function address

cycle_corrector

a value which should be added to the cycle counter, zero if omitted.

extra

any extra parameter, zero if omitted.

For example:

     .global fxx
     .type fxx,@function
     fxx:
     .LFrameOffset_fxx=0x08
     .profiler "scdP", fxx     ; function entry.
     			  ; we also demand stack value to be saved
       push r11
       push r10
       push r9
       push r8
     .profiler "cdpt",fxx,0, .LFrameOffset_fxx  ; check stack value at this point
     					  ; (this is a prologue end)
     					  ; note, that spare var filled with
     					  ; the farme size
       mov r15,r8
     ...
     .profiler cdE,fxx         ; check stack
       pop r8
       pop r9
       pop r10
       pop r11
     .profiler xcde,fxx,3      ; exit adds 3 to the cycle counter
       ret                     ; cause 'ret' insn takes 3 cycles