Bug #22188: Debug symbols missing when compiled with GCC LTO

• Status: Open
• Assignee: -
• Target version: -
• Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN

[rwstauner (Randy Stauner)]

When compiling with LTO (the XCFLAGS and XLDFLAGS below) RUBY_CRASH_REPORT does
not resolve symbols.

(
  export optflags="-O3" cflags="-fno-omit-frame-pointer"
  export XCFLAGS="-flto=auto -ffat-lto-objects -Werror=lto-type-mismatch"
  export XLDFLAGS="-flto=auto -ffat-lto-objects"

  ./configure --disable-install-doc --disable-shared
  make -j miniruby
)

Simple crash simulation:

./miniruby -e 'Process.kill("SEGV", $$)'

On master the output includes:

-- C level backtrace information -------------------------------------------
/src/miniruby(0x5608c71bafdd) [0x5608c71bafdd]
/src/miniruby(0x5608c71c6f46) [0x5608c71c6f46]
/src/miniruby(0x5608c6f31370) [0x5608c6f31370]
/src/miniruby(0x5608c70e3150) [0x5608c70e3150]
/usr/lib/libc.so.6(0x7f62122ac2d0) [0x7f62122ac2d0]
/usr/lib/libc.so.6(kill+0xb) [0x7f62122ac4db]
/src/miniruby(0x5608c70e1a65) [0x5608c70e1a65]
/src/miniruby(0x5608c7189d1e) [0x5608c7189d1e]
/src/miniruby(0x5608c718dea7) [0x5608c718dea7]

/src/miniruby(0x5608c719417e) [0x5608c719417e]

/src/miniruby(0x5608c71b793c) [0x5608c71b793c]
/src/miniruby(0x5608c6f3d13c) [0x5608c6f3d13c]
/src/miniruby(0x5608c6f42321) [0x5608c6f42321]
/src/miniruby(0x5608c6e4f9b3) [0x5608c6e4f9b3]
/usr/lib/libc.so.6(0x7f62122956c1) [0x7f62122956c1]
/usr/lib/libc.so.6(__libc_start_main+0x89) [0x7f62122957f9]
[0x5608c6e4f9f5]

With a tiny change to fall back to symtab (even after parsing DWARF) we can get this
(empty lines added for comparison with next block):

-- C level backtrace information -------------------------------------------
/src/miniruby(rb_print_backtrace+0x1d) [0x55f6397aafdd] /src/vm_dump.c:1111

/src/miniruby(rb_vm_bugreport+0xa26) [0x55f6397b6f46] /src/vm_dump.c:1473

/src/miniruby(rb_bug_for_fatal_signal+0x110) [0x55f639521370] /src/error.c:1140
/src/miniruby(sigsegv+0x50) [0x55f6396d3150] /src/signal.c:948
/usr/lib/libc.so.6(0x7f991555d2d0) [0x7f991555d2d0]
/usr/lib/libc.so.6(kill+0xb) [0x7f991555d4db]
/src/miniruby(rb_f_kill+0x205) [0x55f6396d1a65] /src/signal.c:487
/src/miniruby(vm_call_cfunc_with_frame_+0xfe) [0x55f639779d1e] /src/vm_insnhelper.c:3821

/src/miniruby(vm_sendish.constprop.0+0xb7) [0x55f63977dea7] /src/vm_insnhelper.c:6056
/src/miniruby(vm_exec_core.lto_priv.0+0x6e) [0x55f63978417e] /src/insns.def:909
/src/miniruby(rb_vm_exec+0xec) [0x55f6397a793c] /src/vm.c:2825

/src/miniruby(rb_ec_exec_node+0xac) [0x55f63952d13c] /src/eval.c:284
/src/miniruby(ruby_run_node+0x61) [0x55f639532321] /src/eval.c:322
/src/miniruby(main+0x63) [0x55f63943f9b3] ./main.c:42

PR: https://github.com/ruby/ruby/pull/17743

Currently the code in addr2line.c has a stub:

case DW_FORM_ref_addr:
  goto finish; /* not supported yet */

If we add support for that we can get better names and inlined frames
(empty lines added for comparison with previous block):

-- C level backtrace information -------------------------------------------
/src/miniruby(rb_print_backtrace+0x1d) [0x55cd045f81dd] /src/vm_dump.c:1111

/src/miniruby(fprintf+0x0) [0x55cd04604146] /src/vm_dump.c:1473
/src/miniruby(rb_vm_bugreport) /src/vm_dump.c:1476

/src/miniruby(rb_bug_for_fatal_signal+0x110) [0x55cd0436e370] /src/error.c:1140
/src/miniruby(sigsegv+0x50) [0x55cd04520150] /src/signal.c:948
/usr/lib/libc.so.6(0x7f9ef85522d0) [0x7f9ef85522d0]
/usr/lib/libc.so.6(kill+0xb) [0x7f9ef85524db]
/src/miniruby(rb_f_kill+0x205) [0x55cd0451ea65] /src/signal.c:487
/src/miniruby(vm_call_cfunc_with_frame_+0xfe) [0x55cd045c6f1e] /src/vm_insnhelper.c:3821

/src/miniruby(vm_sendish+0xb7) [0x55cd045cb0a7] /src/vm_insnhelper.c:6056
/src/miniruby(vm_exec_core+0x6e) [0x55cd045d137e] /src/insns.def:909
/src/miniruby(vm_exec_loop+0x16) [0x55cd045f4b3c] /src/vm.c:2825
/src/miniruby(rb_vm_exec) /src/vm.c:2801

/src/miniruby(rb_ec_exec_node+0xac) [0x55cd0437a13c] /src/eval.c:284
/src/miniruby(ruby_run_node+0x61) [0x55cd0437f321] /src/eval.c:322
/src/miniruby(rb_main+0x22) [0x55cd0428c9b3] ./main.c:42

/src/miniruby(main) ./main.c:62
/usr/lib/libc.so.6(0x7f9ef853b6c1) [0x7f9ef853b6c1]
/usr/lib/libc.so.6(__libc_start_main+0x89) [0x7f9ef853b7f9]
/src/miniruby(_start+0x25) [0x55cd0428c9f5] ./main.c:63

PR: https://github.com/ruby/ruby/pull/17744

[rwstauner (Randy Stauner)]

• Description updated (diff)