digitalmars.D.learn - Returning structs from COM
- John C (24/24) Dec 03 2016 Some DirectX methods return structs by value, but when I try
- Nicholas Wilson (3/6) Dec 03 2016 I know for ldc that function that return struct by value actually
- evilrat (9/33) Dec 18 2016 most likely due to this
- kinke (15/42) Dec 19 2016 That's rather interesting. The COM function really seems to
Some DirectX methods return structs by value, but when I try
calling them I either get garbage or an access violation.
Usually COM methods return structs by pointer as a parameter, but
these are returning the struct as the actual return value, as in
this definition:
extern(Windows):
struct D2D1_SIZE_F { float width, height; }
interface ID2D1Bitmap : ID2D1Image {
D2D1_SIZE_F GetSize();
}
If I rewrite GetSize to return by pointer as a parameter, it
appears to work and I get the correct width and height without an
AV being thrown. And I can add a helper method that returns by
value:
interface ID2D1Bitmap : ID2D1Image {
void GetSize(D2D1_SIZE_F* size);
final D2D1_SIZE_F GetSize() {
D2D1_SIZE_F size;
GetSize(&size);
return size;
}
}
But does anyone know why the original definition works in C++ but
not D? Is it a bug? (I'm compiling with -m64.)
Dec 03 2016
Nicholas Wilson <iamthewilsonator hotmail.com> On Saturday, 3 December 2016 at 09:51:00 UTC, John C wrote:Some DirectX methods return structs by value, but when I try calling them I either get garbage or an access violation. [...]I know for ldc that function that return struct by value actually return by a hidden return parameter pointer.
Dec 03 2016
On Saturday, 3 December 2016 at 09:51:00 UTC, John C wrote:
Some DirectX methods return structs by value, but when I try
calling them I either get garbage or an access violation.
Usually COM methods return structs by pointer as a parameter,
but these are returning the struct as the actual return value,
as in this definition:
extern(Windows):
struct D2D1_SIZE_F { float width, height; }
interface ID2D1Bitmap : ID2D1Image {
D2D1_SIZE_F GetSize();
}
If I rewrite GetSize to return by pointer as a parameter, it
appears to work and I get the correct width and height without
an AV being thrown. And I can add a helper method that returns
by value:
interface ID2D1Bitmap : ID2D1Image {
void GetSize(D2D1_SIZE_F* size);
final D2D1_SIZE_F GetSize() {
D2D1_SIZE_F size;
GetSize(&size);
return size;
}
}
But does anyone know why the original definition works in C++
but not D? Is it a bug? (I'm compiling with -m64.)
most likely due to this
https://issues.dlang.org/show_bug.cgi?id=16527
and that is annoying. i tried ldc2 1.1.beta6 and dmd 2.072.1 both
x86 and x64 and it crashes anyways, sooner or later.
btw if you make call with return pointer instead of value it can
probably messed up your stack already and crash any moment later.
in my DirectX bindings i used to return ref struct(though i think
this is dirty hack), and it was working until recent.
Dec 18 2016
On Saturday, 3 December 2016 at 09:51:00 UTC, John C wrote:Some DirectX methods return structs by value, but when I try calling them I either get garbage or an access violation. Usually COM methods return structs by pointer as a parameter, but these are returning the struct as the actual return value, as in this definition: extern(Windows): struct D2D1_SIZE_F { float width, height; } interface ID2D1Bitmap : ID2D1Image { D2D1_SIZE_F GetSize(); } If I rewrite GetSize to return by pointer as a parameter, it appears to work and I get the correct width and height without an AV being thrown. And I can add a helper method that returns by value: interface ID2D1Bitmap : ID2D1Image { void GetSize(D2D1_SIZE_F* size); final D2D1_SIZE_F GetSize() { D2D1_SIZE_F size; GetSize(&size); return size; } } But does anyone know why the original definition works in C++ but not D? Is it a bug? (I'm compiling with -m64.)That's rather interesting. The COM function really seems to return the struct directly, not returning an HRESULT and setting some output pointee as most COM functions I've seen so far. According to the Win64 ABI, the returned D2D1_SIZE_F struct should be returned in RAX, as the 2 floats are <= 64 bit. But your workaround seems to suggest it's using sret (struct-return via hidden pointer). To make sure this is the case, I'd suggest inspecting the C++ assembly for a trivial function. If so, we'll need to find out why the Win64 ABI isn't followed and whether COM has its own ABI.I know for ldc that function that return struct by value actually return by a hidden return parameter pointer.Not always. In fact, it highly depends on the target ABI which structs are returned in registers and which ones via sret.https://issues.dlang.org/show_bug.cgi?id=16527That is definitely a bug in DMD (swapping `this` and `sret` pointers) but doesn't apply to LDC, and is a separate issue.
Dec 19 2016
On Monday, 19 December 2016 at 09:49:13 UTC, kinke wrote:On Saturday, 3 December 2016 at 09:51:00 UTC, John C wrote:yes it works indeed O_o also align(8) for struct seems to work in x86 but has some issues with ESP(reserved 4 bytes for pointer, still has 4 bytes for second float?), crashes without align at later point. x64 still has messed up 'this'(both dmd and ldc, not tested with gdc), but with passing parameter instead of return it really keeps stack where it leaves it and even 'this' are in place so everything is seems to work.Some DirectX methods return structs by value, but when I try calling them I either get garbage or an access violation. Usually COM methods return structs by pointer as a parameter, but these are returning the struct as the actual return value, as in this definition: extern(Windows): struct D2D1_SIZE_F { float width, height; } interface ID2D1Bitmap : ID2D1Image { D2D1_SIZE_F GetSize(); } If I rewrite GetSize to return by pointer as a parameter, it appears to work and I get the correct width and height without an AV being thrown. And I can add a helper method that returns by value: interface ID2D1Bitmap : ID2D1Image { void GetSize(D2D1_SIZE_F* size); final D2D1_SIZE_F GetSize() { D2D1_SIZE_F size; GetSize(&size); return size; } }
Dec 19 2016
On Monday, 19 December 2016 at 12:23:46 UTC, evilrat wrote:x64 still has messed up 'this'(both dmd and ldc, not tested with gdc)Please file an LDC issue then, as I'm pretty sure it works for regular (non-COM) C++ classes.
Dec 19 2016
On Monday, 19 December 2016 at 09:49:13 UTC, kinke wrote:That's rather interesting. The COM function really seems to return the struct directly, not returning an HRESULT and setting some output pointee as most COM functions I've seen so far. According to the Win64 ABI, the returned D2D1_SIZE_F struct should be returned in RAX, as the 2 floats are <= 64 bit. But your workaround seems to suggest it's using sret (struct-return via hidden pointer). To make sure this is the case, I'd suggest inspecting the C++ assembly for a trivial function. If so, we'll need to find out why the Win64 ABI isn't followed and whether COM has its own ABI.I did some research myself and indeed, COM classes/interfaces are apparently subject to a separate ABI. Unfortunately, googling it hasn't turned up any official (and not even some inofficial) documentation so far. Based on the first few tests on Win64, integers are returned in RAX, floats (and I guess doubles too) in XMM0, and structs (incl. 2x int32 and 2x float) via hidden sret pointer, with `this` pointer in RCX (1st arg) and `sret` in RDX (2nd arg). Compared to the normal Win64 C++ ABI it just seems more conservative by always returning structs via hidden pointer.
Dec 19 2016
https://issues.dlang.org/show_bug.cgi?id=16987 https://github.com/ldc-developers/ldc/issues/1935
Dec 19 2016
On Monday, 19 December 2016 at 22:47:26 UTC, kinke wrote:On Monday, 19 December 2016 at 09:49:13 UTC, kinke wrote:Wow! That was quick. Such tests would take me few days. I'm not sure how it may help but there is "specs" in MS .net core runtime, just search the repo for COM like this https://github.com/dotnet/coreclr/blob/32f0f9721afb584b4a14d69135bea7ddc129f755/src/vm/amd64/GenericComCallStubs.asm#L177[...]I did some research myself and indeed, COM classes/interfaces are apparently subject to a separate ABI. Unfortunately, googling it hasn't turned up any official (and not even some inofficial) documentation so far. Based on the first few tests on Win64, integers are returned in RAX, floats (and I guess doubles too) in XMM0, and structs (incl. 2x int32 and 2x float) via hidden sret pointer, with `this` pointer in RCX (1st arg) and `sret` in RDX (2nd arg). Compared to the normal Win64 C++ ABI it just seems more conservative by always returning structs via hidden pointer.
Dec 19 2016