create a real call graph that can have cycles in --graphviz #1500
Description
uftrace graph actually doesn't show a call graph, but just a call tree output. For example, t-fibonacci example's output is as follows.
$ gcc -pg -o t-fibonacci tests/s-fibonacci.c
$ uftrace record t-fibonacci
$ uftrace graph
# Function Call Graph for 't-fibonacci' (session: 7701e718f823010e)
========== FUNCTION CALL GRAPH ==========
# TOTAL TIME FUNCTION
20.354 us : (1) t-fibonacci
2.199 us : +-(1) __monstartup
: |
1.129 us : +-(1) __cxa_atexit
: |
17.026 us : +-(1) main
16.499 us : (1) fib
15.859 us : (2) fib
14.887 us : (4) fib
12.782 us : (8) fib
8.362 us : (14) fib
2.976 us : (10) fib
0.390 us : (2) fib
As the output shows there are multiple nodes for fib function. It's because there are multiple backtrace or call paths of each fib node.
The --graphviz output also uses the same logic when building a graph, precisely a tree. So its output doesn't show the multiple nodes for the same function, but it draws multiple edges for the same calls.
The --graphviz output of t-fibonacci is as follows.
$ gcc -pg -o t-fibonacci tests/s-fibonacci.c
$ uftrace record t-fibonacci
$ uftrace dump --graphviz
...
digraph G {
"t-fibonacci"
"t-fibonacci" -> "__monstartup" [xlabel = "1"]
"t-fibonacci" -> "__cxa_atexit" [xlabel = "1"]
"t-fibonacci" -> "main" [xlabel = "1"]
"main" -> "fib" [xlabel = "1"]
"fib" -> "fib" [xlabel = "2"]
"fib" -> "fib" [xlabel = "4"]
"fib" -> "fib" [xlabel = "8"]
"fib" -> "fib" [xlabel = "14"]
"fib" -> "fib" [xlabel = "10"]
"fib" -> "fib" [xlabel = "2"]
}Its image shows too many edges from fib to fib as follows.
But it would be much better to make it as follows.
digraph G {
"t-fibonacci"
"t-fibonacci" -> "__monstartup" [xlabel = "1"]
"t-fibonacci" -> "__cxa_atexit" [xlabel = "1"]
"t-fibonacci" -> "main" [xlabel = "1"]
"main" -> "fib" [xlabel = "1"]
"fib" -> "fib" [xlabel = "40"]
}This modified dot produces much clear image as follows.
