From: xtkoba+ruby@...
Date: 2021-04-17T06:45:08+00:00
Subject: [ruby-core:103491] [Ruby master Bug#17810] addr2line.c: Some symbol names missing in C backtrace with Clang/LLVM

Issue #17810 has been reported by xtkoba (Tee KOBAYASHI).

----------------------------------------
Bug #17810: addr2line.c: Some symbol names missing in C backtrace with Clang/LLVM
https://bugs.ruby-lang.org/issues/17810

* Author: xtkoba (Tee KOBAYASHI)
* Status: Open
* Priority: Normal
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
When Clang/LLVM is used for compilation, some symbol names are missing in C level backtrace information. An example:
```
-- C level backtrace information -------------------------------------------
(...snip...)
/var/tmp/ruby.debug/lib/libruby.so.3.1(vm_call_method_each_type+0x6a) [0x7f73856ac33f] ../vm_insnhelper.c:3438
/var/tmp/ruby.debug/lib/libruby.so.3.1(0x7f73856ac29a) [0x7f73856ac29a]
/var/tmp/ruby.debug/lib/libruby.so.3.1(0x7f73856aadf6) [0x7f73856aadf6]
/var/tmp/ruby.debug/lib/libruby.so.3.1(vm_exec_core+0xff7) [0x7f738569c3cd] ../insns.def:792
/var/tmp/ruby.debug/lib/libruby.so.3.1(rb_vm_exec+0x5c9) [0x7f73856a78d4]
/var/tmp/ruby.debug/lib/libruby.so.3.1(rb_ec_exec_node+0xe5) [0x7f73855a1bec] ../eval.c:320
/var/tmp/ruby.debug/lib/libruby.so.3.1(ruby_run_node+0x5a) [0x7f73855a1acf] ../eval.c:379
/var/tmp/ruby.debug/bin/ruby(main+0x73) [0x55c15877ac4b] ../main.c:47
```

This seems to happen because `dladdr(3)` sometimes fills `NULL` in `dli_sname` which is then overwritten to `lines[i].sname` regardless of its previous value.

A patch is attached to fix this issue. It modifies `addr2line.c` so that it does not use `dli_sname` (and also `dli_fname`) when the value is `NULL`.

I also attach another patch that makes `addr2line.c` print source filename even when source lineno is not available (which is the case for `rb_vm_exec` in the above example).

When these two patches are applied, C level backtrace information is printed as follows.
```
-- C level backtrace information -------------------------------------------
(...snip...)
/var/tmp/ruby.debug/lib/libruby.so.3.1(vm_call_method_each_type+0x6a) [0x7fb08928231f] ../vm_insnhelper.c:3438
/var/tmp/ruby.debug/lib/libruby.so.3.1(vm_call_method+0xf6) [0x7fb08928227a] ../vm_insnhelper.c:0
/var/tmp/ruby.debug/lib/libruby.so.3.1(vm_sendish+0x334) [0x7fb089280dd6] ../vm_insnhelper.c:0
/var/tmp/ruby.debug/lib/libruby.so.3.1(vm_exec_core+0xff7) [0x7fb0892723ad] ../insns.def:792
/var/tmp/ruby.debug/lib/libruby.so.3.1(rb_vm_exec+0x5c9) [0x7fb08927d8b4] ../vm.c:0
/var/tmp/ruby.debug/lib/libruby.so.3.1(rb_ec_exec_node+0xe5) [0x7fb089177bcc] ../eval.c:320
/var/tmp/ruby.debug/lib/libruby.so.3.1(ruby_run_node+0x5a) [0x7fb089177aaf] ../eval.c:379
/var/tmp/ruby.debug/bin/ruby(main+0x73) [0x557ed1e0bc4b] ../main.c:47
```

---Files--------------------------------
ruby-addr2line-do-not-overwrite-sname-with-null.patch (1.07 KB)
ruby-addr2line-print-filename-without-lineno.patch (574 Bytes)


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