How to do code coverage on embedded
I write a project for a non POSIX embedded system so I cannot use gcc option --coverage (i don't have read or write). What else can I do to produce gcov like output. I do have an output function.
Answer
It can be most easily done with by a processor with embedded trace, a board design that exposes the trace port, and a suitable hardware debugger and associate software. For example, many Cortex-M based devices include ARM's embedded trace macrocell (ETM), and this is supported by Keil's uVision IDE and ULINK-Pro debugger to provide code coverage and instruction/source level trace as well as real-time profiling. Hardware trace has the advantage that it is non-intrusive - the code runs in real-time.
If you do not have the hardware support, you may have to resort to simulation. Many tool-chains include an instruction level simulator that will perform trace, code-coverage, and profiling, but you may have to create debug scripts or code stubs to simulate hardware to coerce the execution of all paths.
A third alternative is to build the code on a desktop platform with stubs to replace target hardware dependencies, and perform testing and code coverage on that. You have to trust that the target C compiler and the test system compiler both translate the source with identical semantics. The advantage here is that the debug tools available are often superior to those available to embedded systems. You can also test much of your code before any hardware is available, and in most cases execute code much faster, possibly allowing more extensive testing.
Not having a POSIX API does not preclude using GCC, it merely precludes using the GNU C library. On embedded systems without POSIX, alternative C libraries are used such as Newlib. Newlib has a system porting layer where I/O and basic heap management are implemented.