From: Rei.Odaira@... Date: 2014-03-24T02:55:04+00:00 Subject: [ruby-dev:48068] [ruby-trunk - Bug #9654] Segmentation fault while printing out C level backtrace information Issue #9654 has been updated by Rei Odaira. Thanks for the quick fix. The second segmentation fault no longer happens. Unfortunately, I found another problem regarding the C-level backtrace. Here is what I see in my environment (ruby 2.2.0dev (2014-03-23) [powerpc64-linux]): ~~~ $ ./ruby -e 'Process.kill :SEGV, $$' -e:1: [BUG] Segmentation fault at 0x004731 ruby 2.2.0dev (2014-03-23) [powerpc64-linux] -- Control frame information ----------------------------------------------- c:0003 p:---- s:0009 e:000008 CFUNC :kill c:0002 p:0015 s:0004 E:001b24 EVAL -e:1 [FINISH] c:0001 p:0000 s:0002 E:002384 TOP [FINISH] -- Ruby level backtrace information ---------------------------------------- -e:1:in `
' -e:1:in `kill' -- C level backtrace information ------------------------------------------- ./ruby(rb_vm_bugreport+0x134) [0x20294264] vm_dump.c:58285 ./ruby(report_bug+0x1ac) [0x2030250c] error.c:242232 ./ruby(rb_bug+0xc4) [0x20302844] error.c:255315 ./ruby(sigsegv+0xb0) [0x202064f0] signal.c:15040 (__kernel_sigtramp_rt32+0x0) [0x100360] ./ruby(ruby_kill+0x118) [0x202a2ee8] thread.c:495680 ./ruby(rb_f_kill+0x98) [0x202074f8] signal.c:97721 ./ruby(call_cfunc_m1+0x2c) [0x2027294c] vm_insnhelper.c:10546 ./ruby(vm_call_cfunc_with_frame+0x14c) [0x2027c5ac] vm_insnhelper.c:768981 ./ruby(vm_call_method+0x580) [0x20291c60] vm_method.c:2680506 ./ruby(vm_exec_core+0x2288) [0x202899a8] vm.inc:1934715 ./ruby(vm_exec+0x6f8) [0x2028d8c8] vm.c:2278215 ./ruby(rb_iseq_eval_main+0x2f8) [0x2028def8] vm_insnhelper.c:2310457 ./ruby(ruby_exec_internal+0xe4) [0x20131884] eval.c:153339 ./ruby(ruby_run_node+0xa4) [0x201336c4] eval.c:326460 ./ruby(main+0x5c) [0x2012f77c] main.c:1828 <<<<< snip >>>>> ~~~ The line numbers are incorrect. In DWARF, `line_base` is signed 8 bytes, but `parse_debug_line_cu()` reads `line_base` as `char`, which is not guaranteed as signed in the C language. The following patch will fix this. ~~~ --- addr2line.c (revision 45390) +++ addr2line.c (working copy) @@ -294,7 +294,7 @@ is_stmt = default_is_stmt = *(unsigned char *)p; p++; - line_base = *(char *)p; + line_base = *(signed char *)p; p++; line_range = *(unsigned char *)p; ~~~ ---------------------------------------- Bug #9654: Segmentation fault while printing out C level backtrace information https://bugs.ruby-lang.org/issues/9654#change-45910 * Author: Rei Odaira * Status: Closed * Priority: Normal * Assignee: Yui NARUSE * Category: core * Target version: current: 2.2.0 * ruby -v: ruby 2.2.0dev (2014-03-19) [powerpc64-linux] * Backport: 2.0.0: DONTNEED, 2.1: DONTNEED ---------------------------------------- When SIGSEGV happens, C level backtrace information should be printed out, but the printing-out itself causes another segmentation fault. ~~~ $ ./ruby -e 'Process.kill :SEGV, $$' -e:1: [BUG] Segmentation fault at 0x00584f ruby 2.2.0dev (2014-03-19) [powerpc64-linux] -- Control frame information ----------------------------------------------- c:0003 p:---- s:0009 e:000008 CFUNC :kill c:0002 p:0015 s:0004 E:00153c EVAL -e:1 [FINISH] c:0001 p:0000 s:0002 E:002574 TOP [FINISH] -- Ruby level backtrace information ---------------------------------------- -e:1:in `
' -e:1:in `kill' -- C level backtrace information ------------------------------------------- ./ruby(Segmentation fault ~~~ This second segmentation fault happens at the following stack context. ~~~ (gdb) bt #0 0x201ba994 in strlen () from /lib/libc.so.6 #1 0x2070cbe0 in kvprintf (fmt=0x207a097d "+0x%lx) [0x%lx] %s:%d\n") at addr2line.c:1009 #2 kprintf (fmt=0x207a097d "+0x%lx) [0x%lx] %s:%d\n") at addr2line.c:771 #3 0x2070e4f8 in rb_dump_backtrace_with_lines (num_traces=18, traces=0x2081762c, syms=0x20a7d720) at addr2line.c:677 #4 0x206f3ffc in rb_print_backtrace () at vm_dump.c:690 #5 rb_vm_bugreport () at vm_dump.c:825 #6 0x207621ac in report_bug (file=, line=, fmt=0x2079857c "Segmentation fault at %p", args=0x2085f864) at error.c:312 #7 0x207624e4 in rb_bug (fmt=0x2079857c "Segmentation fault at %p") at error.c:339 #8 0x206664e0 in sigsegv (sig=, info=0x2085f8f0, ctx=) at signal.c:704 #9 #10 0x2016674c in kill () from /lib/libc.so.6 #11 0x20702c64 in ruby_kill (pid=, sig=) at thread.c:5185 <<<<< snip >>>>> ~~~ This error began to occur after this change: http://www.rubyist.net/~kanemoto/chkbuild/plinux/ruby-trunk/log/20140314T070002Z.diff.html.gz Due to this error, `TestBugReporter#test_bug_reporter_add` fails on ppc64 GNU/Linux. My guess is that the changes in addr2line.c are doing something, but I am not sure. The second segmentation fault is caused because `line->sname` points to out-of-range memory. Tracing `rb_dump_backtrace_with_lines()` and `fill_lines()`, I found the `sname` entry was first set correctly by reading the `./ruby` file, but it was later overwritten by some incorrect information while reading the `/usr/lib/debug/lib/libc-2.5.so.debug` file. In `libc-2.5.so.debug`, there seem to be several symbol table entries whose `st_size` is quite big (~1.5 GB), so those entries happen to cover all the addresses in `traces[]`, which results in overwritting `sname` at the line 584 of addr2line.c. I am not familiar with ELF, so I cannot track down further. Hope this report helps. -- https://bugs.ruby-lang.org/