Bug #9654
Updated by nobu (Nobuyoshi Nakada) about 10 years ago
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` 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` line->sname points to out-of-range memory.
Tracing `rb_dump_backtrace_with_lines()` rb_dump_backtrace_with_lines() and `fill_lines()`, fill_lines(), I found the `sname` sname entry was first set correctly by reading the `./ruby` ./ruby file, but it was later overwritten by some incorrect information while reading the `/usr/lib/debug/lib/libc-2.5.so.debug` /usr/lib/debug/lib/libc-2.5.so.debug file.
In `libc-2.5.so.debug`, libc-2.5.so.debug, there seem to be several symbol table entries whose `st_size` st_size is quite big (~1.5 GB), so those entries happen to cover all the addresses in `traces[]`, traces[], which results in overwritting `sname` sname at the line 584 of addr2line.c.
I am not familiar with ELF, so I cannot track down further.
Hope this report helps.