I tried to run a simple in a go script from python and I got a segmentation fault. Here is my code:
main.go
package main
import (
/*
typedef struct foo{
int a;
int b;
int c;
int d;
int e;
int f;
} foo;
*/
"C"
)
func main() {}
//export Foo
func Foo(t []int) C.foo {
return C.foo{}
}
main.py
# loading shared object
lib = cdll.LoadLibrary("main.so")
# go type
class GoSlice(Structure):
_fields_ = [("data", POINTER(c_void_p)), ("len", c_longlong), ("cap", c_longlong)]
lib.Foo.argtypes = [GoSlice]
lib.Foo.restype = c_void_p
t = GoSlice((c_void_p * 5)(1, 2, 3, 4, 5), 5, 5)
f = lib.Foo(t)
print(f)
With that code, I got
140362617287784
[1] 23067 segmentation fault python3 main.py
Now If I remove e and f from the main.go I got
None
and no more segmentation fault.
Why the number of members in the struct does matter here?
[EDIT] Both are running at the same place, I run one command clear && go build -o main.so -buildmode=c-shared main.go && python3 main.py
Answer
Your GO/C code is correct. The problem is in the python script. The lib.Foo.restype = c_void_p call expects a void pointer but the library return a C struct. You need to define the return type a ctypes struct in python then it will work as you expect.
The main.go:
package main
import (
/*
typedef struct foo{
int a;
int b;
int c;
int d;
int e;
int f;
} foo;
*/
"C"
)
func main() {
}
//export Foo
func Foo(t []int) C.foo {
foo := C.foo{}
foo.a = 1 // setting some values to avoid seeing zeros
foo.b = 2
return foo
}
The main.py:
from ctypes import *
# loading shared object
lib = cdll.LoadLibrary("main.so")
# go type
class GoSlice(Structure):
_fields_ = [("data", POINTER(c_void_p)), ("len", c_longlong), ("cap", c_longlong)]
class Foo(Structure):
_fields_ = [('a', c_int),
('b', c_int),
('c', c_int),
('d', c_int),
('e', c_int),
('f', c_int)]
lib.Foo.argtypes = [GoSlice]
lib.Foo.restype = Foo
t = GoSlice((c_void_p * 5)(1, 2, 3, 4, 5), 5, 5)
f = lib.Foo(t)
print(f)
print(f.a)
print(f.b)
Then run go build -o main.so -buildmode=c-shared main.go && python main.py and it will print:
go build -o main.so -buildmode=c-shared main.go && python3 main.py
<__main__.Foo object at 0x102608830>
1
2