Hi. We are consistently getting a
segmentation violation in _ctypes.so in _call_function_pointer() for a specific
function.
The problem disappears if I comment out
statement "Py_XDECREF(error_object)" in callproc.c
_call_function_pointer().
error_object is NULL when seg fault
occurs so Py_XDECREF(error_object) should effectively be doing nothing yet
causes a seg fault.
** I'm not very familiar with mips
assembler or backtraces and would like to understand *why* this problem
occurred and find out if there is an "official" fix or workaround.
The problem function looks like:
int myfunc( tHandle handle, tNames name,
void* pValue ) where "typedef void* tHandle" and "typedef enum {
... } tNames"
so the corresponding python/ctypes call
looks like
mylib = ctypes.CDLL('/lib/mylib.so')
c_value = ctypes.c_uint16( 0x00 )
mylib.myfunc( ctypes.c_void_p( 1 ),
c_int( 4 ), ctypes.cast( ctypes.byref( c_value ), ctypes.c_void_p ) )
<< note: if it looks strange to
init a void* to a 1, this is done because parm type was is declared as
"typedef void* tHandle" and this handle was effectively implemented as
an integer, not a pointer to a structure as you might expect >>
Platform is embedded MIPS (big-endian).
_ctypes is from Python-2.6.1.tar.bz2.
_call_function_pointer() in callproc.c
seg faults at the "Py_XDECREF(error_object)" statement at line 834,
specifically "lw" at offset 126e4 in objdump below.
The error_object pointer is NULL at the
time "Py_XDECREF(error_object)" is called since "flags"
parm is 0x1101, ie: neither FUNCFLAG_USE_ERRNO or FUNCFLAG_USE_LASTERROR are
set.
I believe commenting it out doesn’t
affect program logic in this case since error_object is NULL so nothing needs
to happen: "#define Py_XDECREF(op) if ((op) == NULL) ; else
Py_DECREF(op)".
16:25:59 |
/home/jdama/ccm_wa/atl_client_db/CTA5/Plat/oe/out/work/mips-linux/python-2.6.1-ml5/Python-2.6.1/Modules/_ctypes/callproc.c:832
16:25:59 |
126d8: ae040000 sw a0,0(s0)
16:25:59 |
/home/jdama/ccm_wa/atl_client_db/CTA5/Plat/oe/out/work/mips-linux/python-2.6.1-ml5/Python-2.6.1/Modules/_ctypes/callproc.c:834
16:25:59 |
126dc: 12400006 beqz
s2,126f8 <_CallProc+0x414>
16:25:59 |
126e0: 00000000 nop
=>16:25:59 |
126e4: 8e420000 lw v0,0(s2)
16:25:59 |
126e8: 00000000 nop
16:25:59 |
126ec: 2442ffff addiu v0,v0,-1
16:25:59 |
126f0: 10400065 beqz
v0,12888 <_CallProc+0x5a4>
16:25:59 |
126f4: ae420000 sw v0,0(s2)
16:25:59 |
/home/jdama/ccm_wa/atl_client_db/CTA5/Plat/oe/out/work/mips-linux/python-2.6.1-ml5/Python-2.6.1/Modules/_ctypes/callproc.c:836
16:25:59 |
126f8: 16a0004f bnez
s5,12838 <_CallProc+0x554>
16:25:59 |
126fc: 00000000 nop
DIAG 0x0b: Cause: 0x0b - SIGSEGV:
Segmentation violation
DIAG 0x0b: Reason: code 0x80, Sent by
kernel
DIAG 0x0b: Thread: 5066720 -
"", Priority: 5066552, AppID: 0
DIAG 0x0b: Backtrace: 2b2f66e4
_CallProc+0x400
2b2f687c _CallProc+0x598
MMAP: 2b2e4000-2b303000 r-xp 00000000
00:0d 336528 /usr/lib/python2.6/lib-dynload/_ctypes.so
MMAP: 2b303000-2b342000 ---p 0001f000
00:0d 336528 /usr/lib/python2.6/lib-dynload/_ctypes.so
MMAP: 2b342000-2b345000 rw-p 0001e000
00:0d 336528 /usr/lib/python2.6/lib-dynload/_ctypes.so
2b2f66e4 - 2b2e4000 = 126E4
Thanks,
John Dama
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