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. Thanks! > > Thank you, > > -- > Masami Hiramatsu <mhiramat@xxxxxxxxxx>
