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commented
9 years ago Here's a slightly different version, with some extra print statements.
Debugger output:
$ gdb osurandomtest_debug
GNU gdb 6.8.0.20080328-cvs (cygwin-special)
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "i686-pc-cygwin"...
(gdb) run
Starting program: /home/nagle/rpython-libs/lib/work/osurandomtest_debug
[New thread 3556.0xb44]
Error: dll starting at 0x776f0000 not found.
Error: dll starting at 0x76e80000 not found.
Error: dll starting at 0x776f0000 not found.
Error: dll starting at 0x775f0000 not found.
[New thread 3556.0xb0c]
'\xc8\xaehS<\x1e'
Random byte: None
Program received signal SIGSEGV, Segmentation fault.
__shedskin__::ord (s=0x0) at
/home/nagle/shedskin/shedskin-0.6/shedskin/lib/builtin.hpp:1721
1721 template<class T> inline __ss_int len(T x) { return x->__len__(); }
(gdb) bt
#0 __shedskin__::ord (s=0x0) at
/home/nagle/shedskin/shedskin-0.6/shedskin/lib/builtin.hpp:1721
#1 0x0040de83 in __osurandomtest__::_RandomNameSequence () at
osurandomtest.cpp:28
#2 0x0040df5b in __osurandomtest__::test () at osurandomtest.cpp:42
#3 0x0040d458 in __shedskin__::__start (initfunc=0x40dfb0
<__osurandomtest__::__init()>)
at /home/nagle/shedskin/shedskin-0.6/shedskin/lib/builtin.cpp:2082
#4 0x0040dbd6 in main () at osurandomtest.cpp:71
(gdb)
Note the lines
'\xc8\xaehS<\x1e'
Random byte: None
6 random bytes were generated, and "repr" printed them as a string. But "ord"
returned 0, and then led to a crash.
What puzzles me is that if I replace the call to os.urandom with something like
bt = "ABCDEF"
the code does not crash.
The debugger says that at the point of the crash, "n" is a null pointer.
That's presumably why "ord" got a segfault. But n should be a pointer to a
one-character string at that point, obtained from subscripting "bt". I can
dump "bt":
(gdb) print *bt
$3 = {<__shedskin__::pyseq<__shedskin__::str*>> =
{<__shedskin__::pyiter<__shedskin__::str*>> = {<__shedskin__::pyobj> = {<gc> =
{<N
o data fields>}, _vptr$pyobj = 0x433ec8, __class__ = 0xbf0fa8}, <No data
fields>},
units = {<std::_Vector_base<__shedskin__::str*, gc_allocator<__shedskin__::str*> >> = {
_M_impl = {<gc_allocator<__shedskin__::str*>> = {<No data fields>}, _M_start = 0x0, _M_finish = 0x0,
_M_end_of_storage = 0x0}}, <No data fields>}}, unit = {static npos = 4294967295,
_M_dataplus = {<gc_allocator<char>> = {<No data fields>}, _M_p = 0xbf2774 "?hS<\036"}}, hash = -1}
(gdb)
And "units" of bt:
(gdb) print *bt->units
Structure has no component named operator*.
(gdb) print (*bt)->units
$4 = {<std::_Vector_base<__shedskin__::str*, gc_allocator<__shedskin__::str*>
>> = {
_M_impl = {<gc_allocator<__shedskin__::str*>> = {<No data fields>}, _M_start = 0x0, _M_finish = 0x0,
_M_end_of_storage = 0x0}}, <No data fields>}
which is a null string and shouldn't be.
Also notice that in the stack backtrace, the stack is off; it shows control in
"len", which is wrong. Running without the debugger, I get
$ ./osurandomtest_debug.exe
'8\x00\x16\xd1\xc8\x03'
Random byte: '8'
Random byte as integer: 56
Random byte: '\x00'
Random byte as integer: 0
Random byte: '\x16'
Random byte as integer: 22
Random byte: None
2 [main] osurandomtest_debug 3052 exception::handle: Error while dumping state (probably corrupted stack)
Segmentation fault (core dumped)
so something clobbbered the stack.
Original comment by na...@animats.com on 15 Nov 2010 at 4:00
Attachments:
Original issue reported on code.google.com by
na...@animats.comon 15 Nov 2010 at 3:29Attachments: