2015-03-03 13:03, Bruce Richardson: > On Tue, Mar 03, 2015 at 01:56:19PM +0100, Marc Sune wrote: > > On 03/03/15 13:40, Panu Matilainen wrote: > > >My 5c is that if anything, DPDK needs *less* places that muck around with > > >compiler flags, not more. If you something like this for all the libraries > > >in DPDK the number doesn't just increase a bit, it explodes. > > > > If you check the part below this one in my original email, that you stripped > > out (without notice), the suggestion was also to add a global _DEBUG > > parameter for the entire DPDK set of libraries, to change all the CFLAGS at > > once (not in the attached PATCH). > > > > >I dont see that much point in this thing, but I'd approach it by defining > > >the debug flags someplace central, say DEBUG_FLAGS, and append that to the > > >common cflags when *_DEBUG config is enabled. At least with gcc the last > > >option wins so if you just append -O0 when debugging then that's what > > >wins, the earlier -O3 does not matter. > > > > The original problem is the one you expose; libraries hardcode the CFLAGS, > > ignoring user-flags. There is no way to change this unless you change the > > Makefiles directly. > > > > But right now, each library does hardcode its *own* flags (check Makefiles > > for the libraries), so there is already not a unified approach here. I see > > for instance KNI having -fno-strict-aliasing while other libraries don't. > > > > Having said that, there are moments, specially with -O3, in which to be able > > to reproduce a bug, you need to compile certain parts of code with -O3 and > > the rest with -O0 -g (the ones to be debugged). The approach proposed (both > > a global *and* a lib specific) allows that. > > > > Marc > > I believe that the global option of overriding the CFLAGS is already > sufficiently > covered - including being documented in programmers guide - by EXTRA_CFLAGS. > The > ability to turn off optimization support for a single library is not covered > anywhere, and that suggestion seems reasonable to me. For each library, we can > just append '-O0 -g' to the CFLAGS in that libraries makefile if the debug > option > is set. I don't see that as significantly complicating things [though I > wouldn't > make any changes to the rte.app.mk to allow this, just have it per lib in the > lib's makefile]
The difficult thing with a build system, is to know which options and use cases we should support. Today you are suggesting some debug options for gdb. Tomorrow someone would like to have a valgrind support and someone else would like more options for a static analyzer. I think that these usages are restricted to developers use and they already can tune the Makefiles of the libs they are working on.
