There is no documentation that explain map file of PSoC4.
I can find only AN89610 "PSoC® Arm® Cortex® Code Optimization ".
Do you have any document?
Should I refer to GNU Linker like below?
The map file is not specific for PSoC but toolchain specific.
if you use GNU toolchain, you can search "map file" with GNU. (e.g. GNU documentations contained in PSoC Creator, https://gcc.gnu.org/onlinedocs/gcc/ , and so on.)
Here is an example for GNU documentation in PSoC Creator.