On Thu, 2012-11-29 at 15:00 -0800, David Daney wrote: > On 11/29/2012 01:04 PM, Alan Cooper wrote: > > I've been doing some testing of the MIPS Function Tracer functionality > > on the 3.3 kernel. I was surprised to find that the option to generate > > frame pointers was required for tracing. > > It is not really required for MIPS function tracing, but the Kconfigs > for some reason set it. > The issue is with x86. Gcc wont compile if you have -pg and -fomit-frame-pointer on x86. I originally forced function tracing to select FRAME_POINTER, but because now on x86 with -mfentry, -pg no longer requires frame pointers being set, I just let -pg complain one way or the other. I believe that gcc by default will not add frame pointers. Thus adding function tracing just prevents -fomit-frame-pointer from being set, and if -pg requires frame pointers it will automatically enable them otherwise they should not be enabled. -- Steve > > When I don't enable > > FRAME_POINTER along with FUNCTION_TRACER, the kernel hangs on boot. I > > also noticed that a checkin to the 3.4 kernel > > (b732d439cb43336cd6d7e804ecb2c81193ef63b0) no longer forces on > > FRAME_POINTER when FUNCTION_TRACER is selected. I was wondering how it > > works in 3.4 and beyond, so I built a Malta kernel from the latest > > MIPS tree with FUNCTION_TRACING enabled and tested it with QEMU. The > > kernel hung the same way. I can think of 2 reasons for this: > > 1. Function tracing is broken for MIPS in 3.4 and beyond. > > 2. The 4.5.3 GNU C compiler I'm using is generating different code for > > function tracing. >
