[avr-gcc-list] Format of HEX file when program memory addresses exceed 64K

[Graham Davies]

I've spent over an hour looking for this information on the Web and in the 
WinAVR documentation but I can't find it so I'm asking for some pointers.

I'm using WinAVR-20081205 with AVRStudio 4.15, letting the GCC plug-in do 
all the heavy lifting (I'm not writing my own Makefiles or link scripts or 
anthing like that).  The target is an ATmega1280, which is significant to my 
question because it has more than 64Kbytes of program memory.  The output 
format is Intel HEX and I totally grok what I'm getting now as my program 
size is less than 64Kbytes.  I even know where this is coming from.  The 
generated Makefile uses 'avr-objcopy -O ihex' to get this.

What I need to know is what the HEX file is going to look like when my 
program inevitably grows is size above 64Kbytes.  What mechanism will 
'objcopy' use to get above sixteen address bits?  I need to know this 
exactly because I need to write a Flash loader to read such a file.

I just need to know where to look for this information or what to Google 
for.

Thanks, Graham.