How can I see the assembly code that is generated by a gcc (any flavor) compiler for a C/C++ program?
Add -S switch to your command line.
Edit: Do not forget that it will place the assembly to the files you specified under -o switch.
How to restrict it to a specific function or a code block?
Put that function in a separate source file (and use a different command-line parameter for that one source file).
You could also run that program in a debugger like gdb and use a disassembly view. In gdb you could use the command disass/m to view the assembly mixed with the C code on the current location.