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