New submission from Weeble:
I'm not 100% certain this is a bug yet, but I'm beginning to think it's likely.
On 64-bit Linux, I can't pass a struct like this:
struct S { uint8_t data[16]; };
...to a function declared like this:
void f(struct S);
>From experimentation with various integer types and array sizes, it seems this
>causes an abort somewhere in libffi any time the array is between 9 and 16
>bytes in size. If the array is smaller or larger than that, the calls work as
>expected.
I've asked about this here:
http://stackoverflow.com/questions/25487928/is-this-the-correct-way-to-pass-a-struct-by-value-in-ctypes
Here's some test code:
## sum.cpp
#include <cstdint>
using std::size_t;
struct ArrayStruct {
// We'll define ARRAY_TYPE and ARRAY_SIZE on the
// command-line when we compile.
std::ARRAY_TYPE data[ARRAY_SIZE];
};
extern "C" int64_t sum(struct ArrayStruct array)
{
int64_t acc=0;
for (size_t i=0; i!=ARRAY_SIZE; ++i)
{
acc+=array.data[i];
}
return acc;
}
## sum.py
import ctypes
import sys
def main():
array_size = int(sys.argv[1])
array_type = sys.argv[2]
libsum = ctypes.cdll.LoadLibrary('./libsum.so')
ArrType = getattr(ctypes, 'c_' + array_type) * array_size
class MyStruct(ctypes.Structure):
_fields_ = [("data", ArrType)]
m=MyStruct()
for i in range(array_size):
m.data[i]=i
print(libsum.sum(m))
if __name__ == '__main__':
main()
## Build/run
$ g++ -g -shared -Wall -fPIC sum.cpp -o libsum.so -std=c++11 -D
ARRAY_SIZE=16 -D ARRAY_TYPE=uint8_t && python3 sum.py 16 uint8
Aborted (core dumped)
I poked around a little bit in gdb. It's aborting in libffi's "ffi_call"
function: https://github.com/atgreen/libffi/blob/v3.0.13/src/x86/ffi64.c#L516
(gdb) bt
#0 0x00007ffff782cf79 in __GI_raise (sig=sig@entry=6) at
../nptl/sysdeps/unix/sysv/linux/raise.c:56
#1 0x00007ffff7830388 in __GI_abort () at abort.c:89
#2 0x00007ffff67134f5 in ffi_call (cif=0x7fffffffd7b0, fn=0x7ffff650c625
<sum(ArrayStruct)>, rvalue=0x7fffffffd6f0, avalue=0x7fffffffd6d0) at
../src/x86/ffi64.c:516
#3 0x00007ffff691fee3 in _ctypes_callproc () from
/usr/lib/python3.4/lib-dynload/_ctypes.cpython-34m-x86_64-linux-gnu.so
#4 0x00007ffff6920578 in ?? () from
/usr/lib/python3.4/lib-dynload/_ctypes.cpython-34m-x86_64-linux-gnu.so
#5 0x000000000043810a in PyObject_Call ()
#6 0x0000000000579f45 in PyEval_EvalFrameEx ()
#7 0x000000000057d3d3 in PyEval_EvalCodeEx ()
#8 0x000000000057bfaa in PyEval_EvalFrameEx ()
#9 0x000000000057d3d3 in PyEval_EvalCodeEx ()
#10 0x000000000060ba83 in PyRun_FileExFlags ()
#11 0x000000000060bc85 in PyRun_SimpleFileExFlags ()
#12 0x000000000060d3ac in Py_Main ()
#13 0x000000000041ec0d in main ()
(gdb) frame 2
#2 0x00007ffff67134f5 in ffi_call (cif=0x7fffffffd7b0, fn=0x7ffff650c625
<sum(ArrayStruct)>, rvalue=0x7fffffffd6f0, avalue=0x7fffffffd6d0) at
../src/x86/ffi64.c:516
516 abort();
(gdb) info args
cif = 0x7fffffffd7b0
fn = 0x7ffff650c625 <sum(ArrayStruct)>
rvalue = 0x7fffffffd6f0
avalue = 0x7fffffffd6d0
(gdb) info locals
a = <optimized out>
j = <optimized out>
size = 8
n = <optimized out>
classes = {X86_64_INTEGER_CLASS, X86_64_NO_CLASS, 4294956784, 32767}
stack = 0x7fffffffd4f0 ""
argp = 0x7fffffffd5a0 "\001"
arg_types = 0x7fffffffd6b0
gprcount = 1
ssecount = <optimized out>
ngpr = 1
nsse = 0
i = <optimized out>
avn = <optimized out>
ret_in_memory = <optimized out>
reg_args = 0x7fffffffd4f0
(gdb) print *cif
$2 = {abi = FFI_UNIX64, nargs = 1, arg_types = 0x7fffffffd6b0, rtype =
0x7ffff6b5e228, bytes = 0, flags = 10}
It looks like we're trying to pass the struct in two registers, which I think
is what's supposed to happen, but something is going wrong with the second
register. It aborted because it has class X86_64_NO_CLASS and that's not
handled by the switch.
I don't know if this is a bug in libffi, or if ctypes is feeding it bad
information, or if I'm feeding ctypes bad information. I hope this information
is useful for anyone investigating.
I get the same abort in both Python 2.7.6 and 3.4.0.
I originally stumbled across this issue trying to use PySDL2:
http://pysdl2.readthedocs.org/en/rel_0_9_3/
I was trying to call SDL_JoystickGetGUIDString, which uses a similar
struct-by-value call:
http://hg.libsdl.org/SDL/file/92ca74200ea5/include/SDL_joystick.h
----------
components: ctypes
messages: 225881
nosy: weeble
priority: normal
severity: normal
status: open
title: abort when passing certain structs by value using ctypes
type: crash
versions: Python 3.4
_______________________________________
Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue22273>
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