On Wed, Jul 22, 2020 at 01:55:42PM -0400, Steven Rostedt wrote: > > Ha! it is trying to convert the "CALL __fentry__" into a NOP and not > > finding the CALL -- because objtool already made it a NOP... > > > > Weird, I thought recordmcount would also write NOPs, it certainly has > > code for that. I suppose we can use CC_USING_NOP_MCOUNT to avoid those, > > but I'd rather Steve explain this before I wreck things further. > > The reason for not having recordmcount insert all the nops, is because > x86 has more than one optimal nop which is determined by the machine it > runs on, and not at compile time. So we figured just updated it then. > > We can change it to be a nop on boot, and just modify it if it's not > the optimal nop already. Right, I throught that's what we'd be doing already, anyway: > That said, Andi Kleen added an option to gcc called -mnop-mcount which > will have gcc do both create the mcount section and convert the calls > into nops. When doing so, it defines CC_USING_NOP_MCOUNT which will > tell ftrace to expect the calls to already be converted. That seems like the much easier solution, then we can forget about recordmcount / objtool entirely for this.
