Someone had posted a neat little trick that I use now.
If you use windows, the two attachments will help. Type %APPDATA% into explorer and then goto folder Microsoft->Windows->SendTo
Place the two files there.
If you don't have windows you will need to invkoe the avr tools, either manually or some other way.
Then turn on verbose mesages in the IDE options dialog so the compile path is shown.
Once compiled, copy path address into explorer to find the .elf file and right click->sendTo->SRAM.bat
It will produce a file called nm_out.txt listing the memory components, where they sit in memory and their size. ( PGM, SRAM )
SRAM starts at address 00800100.
0000062a 00000076 T init
000000dc 0000003e T loop
00000528 0000001e T main
00800110 00000044 B rx_buffer
0000011a 00000012 T setup
008001bf 00000001 b timer0_fract
008001bb 00000004 B timer0_millis
008001b7 00000004 B timer0_overflow_count
00800154 00000044 B tx_buffer
You can see init, loop, main reside in PGM memory, whereas the serial rx_buffer is in SRAM ( 0x44 bytes long )
The second file will produce a text file with the disassembly in it.
it is named sketch