On Mon, 22 Jun 2020 09:01:48 -0400 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > On Mon, 22 Jun 2020 08:27:53 +0800 > Ming Lei <ming.lei@xxxxxxxxxx> wrote: > > > Can you kprobe guys improve the implementation for covering this case? > > For example, put probe on 3) in case the above situation is recognized. > > To do so would require solving the halting problem. > > https://en.wikipedia.org/wiki/Halting_problem > > Or perhaps reading the DWARF output of the compiler to determine if it > optimized the location you are looking for. As far as I can see, gcc-9.3 doesn't generate this information :( Maybe the optimizer forgot to push the tail-call callsite information to dwarf generator when making a recursive tail-call to a loop. > The first case is impossible to solve, the second would take a lot of > work, (are you going to fund it?) What I can provide is "--skip-prologue" option for the perf-probe which will be similar to the "-P" option. If the compiler correctly generates the information, we can enable it automatically. But as far as I can see, it doesn't. [OT] DWARF has its option(and GNU extension) but it seems not correctly implemented yet. http://www.dwarfstd.org/ShowIssue.php?issue=100909.2 What I found on __blkdev_put and the callers, the "tail-call to other function" were recorded as a call-site DIE with DW_AT_tail_call. But if the "tail-call to itself (recursive call)" was expanded as a loop, it was just disappeared. No call-site information, nor the DW_AT_tail_call. Thank you, -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>
