Hello all, the recent work on static PIE support have exposed some fundamental issues in the way profiling support is currently implemented. When -pg is used for linking, the binary will essentially get a copy of libc linked in, but without actually being a static binary. This means that all the functionality that is supposed to be provided by the dynamic linker is pulled in from libc_pg.a and not from the dynamic linker. I see three options going forward for this:
(1) Introduce a dynamic version of libc_pg. (2) Stop pretending that -pg means dynamic linking and implicitly add -static. (3) Stop pretending that -pg makes sense on modern hardware. Fundamentally, I think the third option is the correct way forward. Sample based profiling with the default HZ setting just doesn't give very useful results except for extremely long running processes -- you get a sample every few million CPU cycles and want to extract something useful from that? There are options for doing sample based profiling without -pg. devel/gperftools provides one and doesn't require custom builds of everything. Both GCC and Clang support basic block counting options useful for coverage testing, removing the other case where gperf might have been useful in the past. To fully support gperftools, we need to provide some kernel glue to support stack unwinding across signals, but that's something desirable anyway. dtrace can also be used for profiling. I don't see the point of keeping another library archive for everything in base around... Joerg
