Issue #17656 has been reported by xtkoba (Tee KOBAYASHI).

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

* Author: xtkoba (Tee KOBAYASHI)
* Status: Open
* Priority: Normal
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
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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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