Michael Veksler <[EMAIL PROTECTED]> writes: > I would like to find how to force gcc (and its optimizers): > > 1. Not to move stuff across in_profiler=* assignments, for all > optimizers. This was measured to skew profiling by 10-20% on x86 > Linux, and more than x2 on tiny functions on PPC-AIX (adding an > __asm__ register+memory barrier lowered this to 1-4% on x86, but > not for PPC-AIX's ABI) > 2. Instrument start_profile_function as early as possible in the > profiled function (if possible before most of the preamble). > 3. Instrument finalize _profile_function as late as possible in the > profiled function (if possible after most of the preamble). > 4. Take exceptions into account > 5. Extract the __FUNCTION__ information from inside > start_profile_function() instead of passing it explicitly (debug > info?) > 1. If __FUNCTION__ can be extracted from stack then maybe ditch > in_profiler=* altogether (this way the profiler will be > billed correctly for its time, without such variables). > 2. Use specialized ABI to call *_profile_function, saving up > the need for register save/restore for profiler's function > calls. > > It took me about a week to implement it in C++ using STL (using RAII > and manual instrumentation). I hope that it would take me no more than > two weeks doing this for C. Anything more than will shift my > benefit/cost ration to finding a weaker solution.
It's really a lot easier to do this as a source code modification than as a compiler change. Unless you already have a lot of experience with the compiler, I think you'd be lucky or very good to get it done in two weeks. For the prologue changes look at FUNCTION_PROFILER and friends in the internal documentation. There is currently no support for profiling support in the epilogue. It could be added along the same lines as FUNCTION_PROFILER. If I were you I wouldn't bother with __FUNCTION__ and would just deal with PC addresses. Use a post-processing pass to convert those back into function names, using, e.g., addr2line. Hope this helps. Ian
