ARM Assembly walking the frame pointer with clang -

i'm compiling code clang 3.3 using -pg on arm architecture, , see empty c function:

void do_nothing() { } 

now looks like:

    .section    .text.do_nothing,"ax",%progbits     .globl  do_nothing     .align  2     .type   do_nothing,%function     .code   16     .thumb_func do_nothing:     .fnstart .leh_func_begin1: .lfunc_begin1:     .loc    2 17 0     .save   {r7, lr}     push    {r7, lr}     .setfp  r7, sp     mov r7, sp     bl  mcount(plt)     .loc    2 17 0 prologue_end .ltmp3:     pop {r7, pc} .ltmp4: .ltmp5:     .size   do_nothing, .ltmp5-do_nothing .lfunc_end1: .leh_func_end1:     .fnend 

now understand r7 used frame counter, , can walk backwards through stack , lr of caller of current call stack if -ffunction-section , -no-omit-frame-pointer specified. however, when try write code this, doesn't work:

mcount:         push {r7, lr} @ save off return , current link         push {r0-r4} @ save off arguments         ldr r0, [r7, #4]         mov r1, lr         bl mymcount         pop {r0-r4}         pop {r7, pc} @ restore link , new pc 

r0 wrong here in trying lr of callee, , believe r1 since used mov , don't have full 32 bits that's in lr.

can point out i'm doing wrong?