[ruby-core:108818] [Ruby master Bug#17656] Improper functions shown in C level backtrace information

Issue #17656 has been updated by mame (Yusuke Endoh).

Status changed from Open to Feedback

I couldn't reproduce the issue on AWS Graviton2 instance. Could you elaborate how to reproduce the issue?

```
$ uname -a
Linux rubyci-ubuntu2004-arm 5.13.0-1022-aws #24~20.04.1-Ubuntu SMP Thu Apr 7 22:14:11 UTC 2022 aarch64 aarch64 aarch64 GNU/Linux
```

Here is ruby complied by gcc version 9.4.0:

```
$ ./miniruby -e 'Process.kill :SEGV, $$'
-e:1: [BUG] Segmentation fault at 0x000003f0001c6a1f
ruby 3.2.0dev (2022-06-09T05:39:18Z master 90b240d127) [aarch64-linux]

-- Control frame information -----------------------------------------------
c:0003 p:---- s:0012 e:000011 CFUNC  :kill
c:0002 p:0015 s:0006 e:000005 EVAL   -e:1 [FINISH]
c:0001 p:0000 s:0003 E:001de0 (none) [FINISH]

-- Ruby level backtrace information ----------------------------------------
-e:1:in `<main>'
-e:1:in `kill'

-- Machine register context ------------------------------------------------
  x0: 0x0000000000000000  x1: 0x000000000000000b  x2: 0x0000aaaab69a9ed0
  x3: 0x5345475600000000  x4: 0x0000000000004553  x5: 0x5345475600000000
  x6: 0x0000000000000040  x7: 0x0000000000000007 x18: 0x0000000000000000
 x19: 0x0000000000000001 x20: 0x000000000000000b x21: 0x0000000000000002
 x22: 0x0000ffff81c62048 x23: 0x0000000000000800 x24: 0x00000000001c6a1f
 x25: 0x0000000000000001 x26: 0x0000aaaab699b000 x27: 0x0000ffffc01b7c20
 x28: 0x00000000001c6a1f x29: 0x0000ffffc01b7bb0  sp: 0x0000ffffc01b7bb0
 fau: 0x0000000000000000

-- C level backtrace information -------------------------------------------
/home/mame/ruby/miniruby(rb_vm_bugreport+0x660) [0xaaaab6868408] vm_dump.c:762
/home/mame/ruby/miniruby(rb_bug_for_fatal_signal+0xd0) [0xaaaab66728c8] error.c:822
/home/mame/ruby/miniruby(sigsegv+0x58) [0xaaaab67c08d0] signal.c:964
/home/mame/ruby/miniruby(sigill) (null):0
linux-vdso.so.1(__kernel_rt_sigreturn+0x0) [0xffff8239b78c]
[0xffff820b10b8]
/home/mame/ruby/miniruby(rb_f_kill+0x2c8) [0xaaaab67c1d68] signal.c:481
...
```

Here is ruby complied by clang version 10.0.0-4ubuntu1:

```
$ ./miniruby -e 'Process.kill :SEGV, $$'
-e:1: [BUG] Segmentation fault at 0x000003f0001cd023
ruby 3.2.0dev (2022-06-09T05:39:18Z master 90b240d127) [aarch64-linux]

-- Control frame information -----------------------------------------------
c:0003 p:---- s:0012 e:000011 CFUNC  :kill
c:0002 p:0015 s:0006 e:000005 EVAL   -e:1 [FINISH]
c:0001 p:0000 s:0003 E:002460 (none) [FINISH]

-- Ruby level backtrace information ----------------------------------------
-e:1:in `<main>'
-e:1:in `kill'

-- Machine register context ------------------------------------------------
  x0: 0x0000000000000000  x1: 0x000000000000000b  x2: 0x0000000000000000
  x3: 0x5345475600000000  x4: 0x0000000000000028  x5: 0x5345475600000000
  x6: 0x0000000000000040  x7: 0x0000000000000007 x18: 0x0000000000000000
 x19: 0x000000000000000b x20: 0x0000ffff9256b048 x21: 0x00000000001cd023
 x22: 0x0000000000000002 x23: 0x0000000000000001 x24: 0x0000000000000001
 x25: 0x0000000000000001 x26: 0x0000aaaade9f08d4 x27: 0x0000aaaade9f07fc
 x28: 0x0000000000080b90 x29: 0x0000ffffe4017210  sp: 0x0000ffffe4017150
 fau: 0x0000000000000000

-- C level backtrace information -------------------------------------------
/home/mame/ruby/miniruby(rb_print_backtrace+0x14) [0xaaaade918f70] vm_dump.c:762
/home/mame/ruby/miniruby(rb_vm_bugreport) vm_dump.c:1057

-- Other runtime information -----------------------------------------------
...
```

Looks like vm_dump does not work at all on aarch64 with clang. The proposed patch didn't change it. This might be another issue.



----------------------------------------
Bug #17656: Improper functions shown in C level backtrace information
https://bugs.ruby-lang.org/issues/17656#change-97895

* Author: xtkoba (Tee KOBAYASHI)
* Status: Feedback
* Priority: Normal
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
The following is an example of C backtrace output on aarch64-linux, where `sig_do_nothing` is shown in spite of segfault:
```
-- C level backtrace information -------------------------------------------
/var/tmp/build.debug/aarch64.clang.O0/lib/libruby.so.3.0(rb_print_backtrace+0x24) [0x5500b86c74] vm_dump.c:758
/var/tmp/build.debug/aarch64.clang.O0/lib/libruby.so.3.0(rb_vm_bugreport+0xa8) [0x5500b86d38] vm_dump.c:999
/var/tmp/build.debug/aarch64.clang.O0/lib/libruby.so.3.0(rb_bug_for_fatal_signal+0x108) [0x550092fb7c] error.c:786
/var/tmp/build.debug/aarch64.clang.O0/lib/libruby.so.3.0(sig_do_nothing+0x0) [0x5500abfa90] signal.c:960
/var/tmp/build.debug/aarch64.clang.O0/lib/libruby.so.3.0(sigsegv) (null):0
[0x50c810]
(...)
```

This happens because `backtrace(3)` fills the buffer with the return addresses retrieved from stack frames. A workaround is to subtract 1 from each return address [1], as in the attached patch.

[1] http://lists.dwarfstd.org/pipermail/dwarf-discuss-dwarfstd.org/2020-July/004694.html

---Files--------------------------------
ruby-backtrace-address-off-by-1.patch (470 Bytes)


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