funcname.ksh

#!/usr/bin/env ksh
typeset -a FUNCNAME

function FUNCNAME.get {
    nameref self=${.sh.name}
    if (( .sh.subscript < .sh.level )); then
        trap "(( .sh.level -= .sh.subscript + 1 )); eval '(( .sh.level = ${.sh.level} ))' \; _=\${.sh.fun}" DEBUG
        trap - DEBUG;
    fi

    (( .sh.subscript < .sh.level - 2 )) && self[.sh.subscript + 1]=
}

function f {
    if (($1 < 10)); then
        print -r -- "${FUNCNAME[@]}"
        g $(($1 + 1))
    fi
    print -r -- "${FUNCNAME[@]}"
}

function g {
    if (($1 < 10)); then
        print -r -- "${FUNCNAME[@]}"
        f $(($1 + 1))
    fi
    print -r -- "${FUNCNAME[@]}"
}

#typeset -ft FUNCNAME.get f g
f 0

output

f
g f
f g f
g f g f
f g f g f
g f g f g f
f g f g f g f
g f g f g f g f
f g f g f g f g f
g f g f g f g f g f
f g f g f g f g f g f
g f g f g f g f g f 
f g f g f g f g f  
g f g f g f g f   
f g f g f g f    
g f g f g f     
f g f g f      
g f g f       
f g f        
g f         
f