On Fri, 22 Jul 2022 17:41:20 -0400 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > I think I understand the fentry/ftrace equivalence you see, I remember > > the perl mcount script ;-) > > It's even more than that. We worked with the compiler folks to get fentry > for ftrace purposes (namely to speed it up, and not rely on frame > pointers, which mcount did). fentry never existed until then. Like I said. > fentry was created *for* ftrace. And currently it's x86 specific, as it > relies on the calling convention that a call does both, push the return > address onto the stack, and jump to a function. The blr > (branch-link-register) method is more complex, which is where the > "patchable" work comes from. If you are interested in more details about the birth of fentry, here's the email that started it all: https://lore.kernel.org/lkml/1258657614.22249.824.camel@xxxxxxxxxxxxxxxxxxx/ -- Steve
