Add gprof test code

gprof/README.md

@@ -0,0 +1,29 @@
+Gprof test program
+------------------
+
+ - Needs gprof-enabled CeGCC.
+ - `make` to compile AppMain.exe.
+
+
+## CFLAGS
+
+By default, GCC emits code that is not comformant to [APCS](https://www.cl.cam.ac.uk/~fms27/teaching/2001-02/arm-project/02-sort/apcs.txt).
+Gprof's `_mcount` assumes APCS-compliant and `fp` being present in the binary.
+
+- `-mapcs-frame` is disabled by default for all optimization level
+  - It leads to a crash without APCS. Must be enabled explicitly.
+- `-fno-omit-frame-pointer` is enabled for all optimization level but `-O0`
+  - It might have some effect on the compilation, but not sure
+  - As I experiment unsetting (disabling) this flag, it doesn't crash even with `-O2`
+
+
+## Experiment results: flags' effect
+
+- `-fno-omit-frame-pointer` looks like it has nothing to do with calling convention because of `-mapcs-frame`
+- Optimization other than `-O0` optimizes the func call (inlining etc) and the resulting graph becomes strange (lack of main() etc.)
+
+
+|CFLAGS|Screenshot|
+|:-----|:--------:|
+|`-O0`|<img src="o0.png" width="300px">|
+|`-O2`|<img src="o2.png" width="300px">|