Re: Two ways of receiving arrays on the C ABI
On 2020-10-20 02:16, Ali Çehreli wrote: Everything works at least on Linux. Is this kosher, or am I using some internal knowledge? Yes, you're using some internal knowledge. You cannot assume it works on any other platform or architecture. In theory, the D compiler could choose to change the ABI for passing D arrays and this would break. If fact, the ABI documentation [1] doesn't mention how a D array is passed. A different compiler could choose to pass it differently. [1] https://dlang.org/spec/abi.html#arrays -- /Jacob Carlborg
Re: Two ways of receiving arrays on the C ABI
On 10/19/20 6:28 PM, Nicholas Wilson wrote:> On Tuesday, 20 October 2020
at 00:16:48 UTC, Ali Çehreli wrote:
>> On the D side, both of the following extern(C) functions take the same
>> arguments.
>
> https://github.com/dlang/dmd/pull/8120
>
> there are issues with structs. Not sure about length/ptr.
Thank you, Nic.
I see that doing the following is undefined behavior:
extern(C)
void dFunc(int[] arr) {// <-- Takes slice
assert(arr.equal(3.iota));
}
// A C function
void dFunc(size_t length, int * ptr); // <-- Passes length+pointer
int arr[] = { 0, 1, 2 };
dFunc(3, arr);
C does not define an ABI. So, length+pointer can be passed in any way
from there. The good thing is that D is aware of the "C Application
Binary Interface of the target system"[1] but that means D would support
taking length+pointer as well. Slice arguments are still strictly in
length+pointer order for D.
So, it works on my Linux system by chance.
Ali
[1] https://dlang.org/spec/abi.html
Re: Two ways of receiving arrays on the C ABI
On Tuesday, 20 October 2020 at 00:16:48 UTC, Ali Çehreli wrote: On the D side, both of the following extern(C) functions take the same arguments. https://github.com/dlang/dmd/pull/8120 there are issues with structs. Not sure about length/ptr.
Two ways of receiving arrays on the C ABI
On the D side, both of the following extern(C) functions take the same
arguments.
1) func1 takes .length and .ptr implicitly as parts of a D array:
extern(C)
void func1(int[] arr) {
assert(arr.equal(3.iota));
}
2) func2 takes .length and .ptr separately and then makes a slice
explicitly:
extern(C)
void func2(size_t length, int * ptr) {
auto arr = ptr[0..length];
assert(arr.equal(3.iota));
}
C side declares and calls both of them the same way:
void func1(size_t length, int * ptr);
void func2(size_t length, int * ptr);
int arr[] = { 0, 1, 2 };
func1(3, arr);
func2(3, arr);
Everything works at least on Linux. Is this kosher, or am I using some
internal knowledge?
Here is the ABI spec:
https://dlang.org/spec/abi.html
One of the DConf Online 2020 slides thanks you! ;)
Ali
