[BUG] bpftrace with bashreadline leads to segmentation fault on subprocess of bash

[Officeyutong]

• Terminal1

  root@mnfe-pve:~/bpftime/example/bpftrace# bpftime load bpftrace ./bashreadline.bt 
  [2024-04-11 15:18:15.001] [info] [syscall_context.hpp:86] manager constructed
  [2024-04-11 15:18:15.880] [info] [syscall_server_utils.cpp:24] Initialize syscall server
  [2024-04-11 15:18:15][error][224409] pkey_alloc failed
  [2024-04-11 15:18:15][info][224409] Global shm constructed. shm_open_type 0 for bpftime_maps_shm
  [2024-04-11 15:18:15][info][224409] Global shm initialized
  [2024-04-11 15:18:15][info][224409] Enabling helper groups ufunc, kernel, shm_map by default
  [2024-04-11 15:18:15][info][224409] bpftime-syscall-server started
  Attaching 2 probes...
  [2024-04-11 15:18:15][info][224409] Created uprobe/uretprobe perf event handler, module name /proc/self/exe, offset c8830
  [2024-04-11 15:18:15][info][224409] Created uprobe/uretprobe perf event handler, module name /bin/bash, offset c6c20

• Terminal 2

  root@mnfe-pve:~/bpftime/example/bpftrace# bpftime start bash
  [2024-04-11 15:24:20.717] [info] [agent.cpp:75] Entering bpftime agent
  [2024-04-11 15:24:20.717] [error] [bpftime_shm_internal.cpp:641] pkey_alloc failed
  [2024-04-11 15:24:20.718] [info] [bpftime_shm_internal.cpp:659] Global shm constructed. shm_open_type 1 for bpftime_maps_shm
  [2024-04-11 15:24:20.718] [info] [bpftime_shm_internal.cpp:29] Global shm initialized
  [2024-04-11 15:24:20.719] [info] [bpf_attach_ctx.cpp:171] Register attach-impl defined helper bpf_get_func_arg, index 183
  [2024-04-11 15:24:20.719] [info] [bpf_attach_ctx.cpp:171] Register attach-impl defined helper bpf_get_func_ret_id, index 184
  [2024-04-11 15:24:20.719] [info] [bpf_attach_ctx.cpp:171] Register attach-impl defined helper bpf_get_retval, index 186
  [2024-04-11 15:24:20.719] [info] [agent.cpp:148] Initializing agent..
  [2024-04-11 15:24:20][info][226547] Executable path: /usr/bin/bash
  [2024-04-11 15:24:20][info][226547] Attach successfully
  ^Croot@mnfe-pve:~/bpftime/example/bpftrace#

• Note that we should press ctrl+c after bash was started. This is also a bug.

• If we run a command that would require bash to create a subprocess, it might be terminated with segmentation fault

  root@mnfe-pve:~/bpftime/example/bpftrace# ls
  [2024-04-11 15:25:14.599] [info] [agent.cpp:75] Entering bpftime agent
  [2024-04-11 15:25:14.600] [error] [bpftime_shm_internal.cpp:641] pkey_alloc failed
  [2024-04-11 15:25:14.600] [info] [bpftime_shm_internal.cpp:659] Global shm constructed. shm_open_type 1 for bpftime_maps_shm
  [2024-04-11 15:25:14.600] [info] [bpftime_shm_internal.cpp:29] Global shm initialized
  [2024-04-11 15:25:14.601] [info] [bpf_attach_ctx.cpp:171] Register attach-impl defined helper bpf_get_func_arg, index 183
  [2024-04-11 15:25:14.601] [info] [bpf_attach_ctx.cpp:171] Register attach-impl defined helper bpf_get_func_ret_id, index 184
  [2024-04-11 15:25:14.601] [info] [bpf_attach_ctx.cpp:171] Register attach-impl defined helper bpf_get_retval, index 186
  [2024-04-11 15:25:14.601] [info] [agent.cpp:148] Initializing agent..
  [2024-04-11 15:25:14][info][226931] Executable path: /usr/bin/ls
  [2024-04-11 15:25:14][error][226931] Failed to find module base address for /bin/bash
  Segmentation fault

[yuanrui77]

In order to solve the error reported by Terminal 1, I added print statements to the run_example.py file in bpftime/.github/script and used gdb debugging, which produced the results. The following screenshots are: three comparative screenshots of run_example.py with the print statement position added, and a screenshot of an error reported after setting a breakpoint in gdb debugging.

[Officeyutong]

Reference

This issue is totally unrelated to the example runner script

[yuanrui77]

I'm trying to solve the error in Terminal1. Where do you think I can start to solve it?

[Officeyutong]

I'm trying to solve the error in Terminal1. Where do you think I can start to solve it?

This issue is already assigned to me. If you are interested in bpftime, you may refer to other un-assigned or good first issues. Thank you!

[Officeyutong]

Some investigations:

• The necessarity of Ctrl+C seems to be related with bashrc, if we run bash with --norc, we are then able to trace commands without pressing Ctrl+C