If I try to remake the hex, it will end up about 20 bytes over.

I tried this several times.

What version of the compiler is required?

Under linux, the compiler is installed separately from the arduino environment so might not be the latest one or one too new.

Code was compiled on avr-gcc-4.3.3, using Objective Developments Crosspack distribution for Mac.

I'll update documentation to make this clear.

I tried 4.3.4, same problem (from the arduino-0018 for windows from arduino.cc). I can try their Mac version but I suspect it will be the same.

The problem appears to be that the avr-gcc provided by Ubuntu and Arduino inserts the "zero data and bss" prologue code even though the "-nostartfiles" switch is passed in. I found that when the LDFLAGS in the Makefile includes the "-nostdlib" switch the resulting program is identical to what is provided in binary form (according to the .lst files).

To clarify, modifying line 61 of the Makefile to the following allows me to compile optiboot to less than 512 bytes: override LDFLAGS = -Wl,$(LDSECTION) -Wl,--relax -nostartfiles -nostdlib

I am using avr-gcc 4.3.4 on Ubuntu 10.04. I hope this helps.

-nostdlib works like a charm. Thx

-nostdlib works perfectly with avr-gcc 4.5.1 on linux

Attached the diff + can be pulled from my clone https://code.google.com/r/lifeeth-optiboot/source/diff?spec=svn7139951c381588d85562d64db21a8dc1ca6a7090&r=7139951c381588d85562d64db21a8dc1ca6a7090&format=side&path=/optiboot/bootloaders/optiboot/Makefile

still not in tree? is this project abandoned? last commit was 6 months ago!

Fixed as part of the great optiboot/Arduino sync-up http://code.google.com/p/optiboot/source/detail?r=8559b64fd093d3976cae58778a1540256cde5c8e