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