Why are Tone.cpp and IPAddress.cpp getting built for my project? I'm using avr-size to see the size of library objects to free up some FLASH. Why are Tone.cpp and IPAddress.cpp getting built? e.g.

$ cd /var/folders/3j/6wp3hvrj34n0xg3xzq6vjq380000gn/T/build8391693238079360471.tmp/
localhost:build8391693238079360471.tmp
$ /Applications/Arduino.app/Contents/Resources/Java/hardware/tools/avr/bin/avr-size *.o
   text    data     bss     dec     hex filename
      0       0       0       0       0 CDC.cpp.o
      0       0       0       0       0 HID.cpp.o
   1816       0     170    1986     7c2 HardwareSerial.cpp.o
    512       0       6     518     206 IPAddress.cpp.o
  10186     391     377   10954    2aca MainINOFile.cpp.o
   1872      14       0    1886     75e Print.cpp.o
   1414       1       0    1415     587 Stream.cpp.o
   1365       1      21    1387     56b Tone.cpp.o
      0       0       0       0       0 USBCore.cpp.o
    288       0       4     292     124 WInterrupts.c.o
    306       0       0     306     132 WMath.cpp.o
   4796       1       1    4798    12be WString.cpp.o
     30       0       0      30      1e main.cpp.o
    618       6       0     624     270 malloc.c.o
     56       0       0      56      38 new.cpp.o
    450       0       0     450     1c2 realloc.c.o
    588       0       9     597     255 wiring.c.o
    266       1       0     267     10b wiring_analog.c.o
    550       0       0     550     226 wiring_digital.c.o
    320       0       0     320     140 wiring_pulse.c.o
    260       0       0     260     104 wiring_shift.c.o
$ /Applications/Arduino.app/Contents/Resources/Java/hardware/tools/avr/bin/avr-size */*.o
   text    data     bss     dec     hex filename
   2790       0       0    2790     ae6 DS3231/DS3231.cpp.o
     38       0       1      39      27 EEPROM/EEPROM.cpp.o
   1444       0       0    1444     5a4 LSM303/lsm303.cpp.o
    782       0       0     782     30e Messenger/Messenger.cpp.o
    116       0       1     117      75 SPI/SPI.cpp.o
    142       0       4     146      92 SdFat/MinimumSerial.cpp.o
   2568       0       0    2568     a08 SdFat/Sd2Card.cpp.o
  10644       0       4   10648    2998 SdFat/SdBaseFile.cpp.o
   1322       2       0    1324     52c SdFat/SdFat.cpp.o
    152       0       0     152      98 SdFat/SdFatUtil.cpp.o
    233       0       0     233      e9 SdFat/SdFile.cpp.o
    736       0       0     736     2e0 SdFat/SdStream.cpp.o
   2604       0     523    3127     c37 SdFat/SdVolume.cpp.o
   3395       0       0    3395     d43 SdFat/istream.cpp.o
   1635       0       0    1635     663 SdFat/ostream.cpp.o
    754       0      86     840     348 Wire/Wire.cpp.o
$ /Applications/Arduino.app/Contents/Resources/Java/hardware/tools/avr/bin/avr-size *.elf
   text    data     bss     dec     hex filename
  29204     442    1279   30925    78cd MainINOFile.cpp.elf
As stated the IDE's equivalent to the make will compile anything everything it can find, in scope. But its linker has eliminate garbage enabled, hence anything not called or not static will not be linked into the EXE.

You can "avr-objdump -t" to create a map from your elf. And -d for an assembly listing. As to see exactly what is in the EXE, for your self. You need to enable show verbose output of compilation from the IDE's preferences, to display the temporary directory that contains the elf file. 

example:

C:\DOCUME~1\mflaga\LOCALS~1\Temp\build6395515806682540138.tmp&gt;C:\projects\Arduino\hardware\tools\avr\bin\avr-objdump -t MP3Shield_Library_Demo.cpp.elf &gt; MP3Shield_Library_Demo_wo_mem.cpp.elf.map
C:\DOCUME~1\mflaga\LOCALS~1\Temp\build6395515806682540138.tmp&gt;C:\projects\Arduino\hardware\tools\avr\bin\avr-objdump -d MP3Shield_Library_Demo.cpp.elf &gt; MP3Shield_Library_Demo_wo_mem.cpp.elf.lst


I did the above and commented out a call to a function member of my library, between subsequent builds. To see that the code was not linked into the assembly.