On Mon, 23 Aug 2021 22:12:06 -0700 Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > On Thu, Jul 29, 2021 at 4:35 PM Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote: > > > > On Thu, 29 Jul 2021 23:05:56 +0900 > > Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote: > > > > > Hello, > > > > > > This is the 10th version of the series to fix the stacktrace with kretprobe on x86. > > > > > > The previous version is here; > > > > > > https://lore.kernel.org/bpf/162601048053.1318837.1550594515476777588.stgit@devnote2/ > > > > > > This version is rebased on top of new kprobes cleanup series(*1) and merging > > > Josh's objtool update series (*2)(*3) as [6/16] and [7/16]. > > > > > > (*1) https://lore.kernel.org/bpf/162748615977.59465.13262421617578791515.stgit@devnote2/ > > > (*2) https://lore.kernel.org/bpf/20210710192433.x5cgjsq2ksvaqnss@treble/ > > > (*3) https://lore.kernel.org/bpf/20210710192514.ghvksi3ozhez4lvb@treble/ > > > > > > Changes from v9: > > > - Add Josh's objtool update patches with a build error fix as [6/16] and [7/16]. > > > - Add a API document for kretprobe_find_ret_addr() and check cur != NULL in [5/16]. > > > > > > With this series, unwinder can unwind stack correctly from ftrace as below; > > > > > > # cd /sys/kernel/debug/tracing > > > # echo > trace > > > # echo 1 > options/sym-offset > > > # echo r vfs_read >> kprobe_events > > > # echo r full_proxy_read >> kprobe_events > > > # echo traceoff:1 > events/kprobes/r_vfs_read_0/trigger > > > # echo stacktrace:1 > events/kprobes/r_full_proxy_read_0/trigger > > > # echo 1 > events/kprobes/enable > > > # cat /sys/kernel/debug/kprobes/list > > > ffffffff8133b740 r full_proxy_read+0x0 [FTRACE] > > > ffffffff812560b0 r vfs_read+0x0 [FTRACE] > > > # echo 0 > events/kprobes/enable > > > # cat trace > > > # tracer: nop > > > # > > > # entries-in-buffer/entries-written: 3/3 #P:8 > > > # > > > # _-----=> irqs-off > > > # / _----=> need-resched > > > # | / _---=> hardirq/softirq > > > # || / _--=> preempt-depth > > > # ||| / delay > > > # TASK-PID CPU# |||| TIMESTAMP FUNCTION > > > # | | | |||| | | > > > <...>-134 [007] ...1 16.185877: r_full_proxy_read_0: (vfs_read+0x98/0x180 <- full_proxy_read) > > > <...>-134 [007] ...1 16.185901: <stack trace> > > > => kretprobe_trace_func+0x209/0x300 > > > => kretprobe_dispatcher+0x4a/0x70 > > > => __kretprobe_trampoline_handler+0xd4/0x170 > > > => trampoline_handler+0x43/0x60 > > > => kretprobe_trampoline+0x2a/0x50 > > > => vfs_read+0x98/0x180 > > > => ksys_read+0x5f/0xe0 > > > => do_syscall_64+0x37/0x90 > > > => entry_SYSCALL_64_after_hwframe+0x44/0xae > > > <...>-134 [007] ...1 16.185902: r_vfs_read_0: (ksys_read+0x5f/0xe0 <- vfs_read) > > > > > > This shows the double return probes (vfs_read() and full_proxy_read()) on the stack > > > correctly unwinded. (vfs_read() returns to 'ksys_read+0x5f' and full_proxy_read() > > > returns to 'vfs_read+0x98') > > > > > > This also changes the kretprobe behavisor a bit, now the instraction pointer in > > > the 'pt_regs' passed to kretprobe user handler is correctly set the real return > > > address. So user handlers can get it via instruction_pointer() API, and can use > > > stack_trace_save_regs(). > > > > > > You can also get this series from > > > git://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git kprobes/kretprobe-stackfix-v9 > > > > Oops, this is of course 'kprobes/kretprobe-stackfix-v10'. And this branch includes above (*1) series. > > Hi Masami, > > Was this ever merged/applied? This is a very important functionality > for BPF kretprobes, so I hope this won't slip through the cracks. No, not yet as far as I know. I'm waiting for any comment on this series. Since this is basically x86 ORC unwinder improvement, this series should be merged to -tip tree. Ingo and Josh, Could you give me any comment, please? Thank you, > Thanks! > > > > > Thank you, > > > > -- > > Masami Hiramatsu <mhiramat@xxxxxxxxxx> -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>
