On Fri, Apr 27, 2012 at 02:46:39PM -0400, Steven Rostedt wrote: > I have code that implements -mfentry for the function tracer. > > For those that are unfamiliar with this, it was introduced into gcc in > 4.6.0 for x86 only. Used with the -pg option, it replaces mcount with > fentry, and is placed at the first instruction of a function (instead of > after the frame has been built, as mcount does). > > So what's my problem? With -mfentry, function tracer does not depend on > frame pointers. As frame pointers may add overhead, some distros > (Debian) has disabled frame pointers from their kernels and with that, > has also disabled function tracing. > > Currently, function tracing selects CONFIG_FRAME_POINTER for various > archs (including x86), as the kernel will not compile without it, if > function tracing is enabled. But if -mfentry is available with the > compiler, it does not have this dependency. The kernel will compile fine > with -pg -mfentry and without frame pointers. > > My question is, how do I remove the dependency in kconfig based on the > compiler? Allow the user to select one of: 1) function tracer 2) frame pointer 3) none of the above This should be trivial to do in Kconfig language. If "function tracer" is selected then use -mfentry if supported, with a fallback to frame pointers. This looks simple IMO and should be easy to implement too. Sam -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
