Bug #21289: Fix C level backtraces for USE_ELF

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 3.4.3 (2025-04-14 revision d0b7e5b6a0) +PRISM [x86_64-linux]
• Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: DONE

[dodecadaniel (Daniel Colson)]

After upgrading GitHub to Ruby 3.4 we noticed that we stopped getting useful C level backtrace information in our crash reports. We traced it back to https://github.com/ruby/ruby/commit/7dd2afbe3a14d021e5554288517709f5778c3d58.

Passing 0 instead of -1 makes sense for the Mach-O version of fill_lines, but there is a separate ELF version of fill_lines that still has special handling for -1: https://github.com/ruby/ruby/blob/58e3aa02240a9ec1b5fe6ce60d63828c2cf0c73a/addr2line.c#L2178-L2209. More details in the corresponding PR: https://github.com/ruby/ruby/pull/13195

[k0kubun (Takashi Kokubun)]

• Backport changed from 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN to 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: REQUIRED

[dodecadaniel (Daniel Colson)]

• Description updated (diff)

[dodecadaniel (Daniel Colson)]

• Status changed from Open to Closed

Applied in changeset git|48a360baa4570a31d760040118d005bb656c6389.

---

Fix C level backtraces for USE_ELF

After upgrading GitHub to Ruby 3.4 we noticed that we stopped getting
useful C level backtrace information in our crash reports. We traced it
back to https://github.com/github/ruby/commit/7dd2afbe3a14d021e5554288517709f5778c3d58.

Passing 0 instead of -1 made sense for the Mach-O version of
fill_lines, but there is a separate ELF version of fill_lines that
still has special handling for -1: https://github.com/ruby/ruby/blob/58e3aa02240a9ec1b5fe6ce60d63828c2cf0c73a/addr2line.c#L2178-L2209

Without this special handling for the main executable, we don't have the
right base_addr when reading debug info, and so we fail to populate
the information for that line: https://github.com/ruby/ruby/blob/58e3aa02240a9ec1b5fe6ce60d63828c2cf0c73a/addr2line.c#L1948
Then we get to https://github.com/ruby/ruby/blob/58e3aa02240a9ec1b5fe6ce60d63828c2cf0c73a/addr2line.c#L2649,
and potentially (depending on how things were run) get back "ruby" as
info.dli_fname instead of the absolute path for the executable. We set
that as the binary_filename and then try to open it inside the next
call to fill_lines, but that fails (unless you happen to be in the
directory where the ruby executable lives) and break out of filling
lines entirely: https://github.com/ruby/ruby/blob/58e3aa02240a9ec1b5fe6ce60d63828c2cf0c73a/addr2line.c#L2673-L2674

This commit treats offset 0 as the main executable, rather than having
a special meaning for -1 (which gets turned into 0 anyway).

[Bug #21289]

[k0kubun (Takashi Kokubun)]

• Backport changed from 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: REQUIRED to 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: DONE

ruby_3_4 ac311437d3c4d60fe4ac100e9652b0cbc3e5f481.