From: Rei.Odaira@...
Date: 2014-03-20T01:59:52+00:00
Subject: [ruby-dev:48058] [ruby-trunk - Bug #9654] [Open] Segmentation fault while printing out C level backtrace information

Issue #9654 has been reported by Rei Odaira.

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Bug #9654: Segmentation fault while printing out C level backtrace information
https://bugs.ruby-lang.org/issues/9654

* Author: Rei Odaira
* Status: Open
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
* ruby -v: ruby 2.2.0dev (2014-03-19) [powerpc64-linux]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN
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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 `<main>'
-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=<value optimized out>, 
    line=<value optimized out>, 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=<value optimized out>, info=0x2085f8f0, 
    ctx=<value optimized out>) at signal.c:704
#9  <signal handler called>
#10 0x2016674c in kill () from /lib/libc.so.6
#11 0x20702c64 in ruby_kill (pid=<value optimized out>, 
    sig=<value optimized out>) 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.




-- 
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