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