The quick answer for older versions of the compiler given by George (see down in the comments) is to simply replace the xclm. The packupperbyte keyword allows access to the upper byte of FLASH on dsPIC and PIC24 devices. For details on this interface, see the compiler user's guide. First things first, how to get this (that is, an XC32 which optimizes) in the easiest way. A Common C Interface (CCI) is available for this compiler as well as the MPLAB XC8 and MPLAB XC32 compilers. Since this is by far the most popular article on my site, I decided to tidy it up somewhat. What?! It is a God-damned GPLed software, or at least to conform with GPL, it must be! So let's see, either compile it from source, or let FSF and the lawyers solve it.
It's Microchip's XC32 compiler, which is based on the GPL-ed GCC, but the same time in the IDE, it shows that it's optimizations are disabled: to enable them, one is supposed to buy the Pro version. At work I recently ran across an interesting, and the same time kind of scary situation.
