> On Mar 22, 2016, at 5:57 AM, Bryan Chan via swift-dev <swift-dev@swift.org>
> wrote:
>
> I tried to google for an answer but couldn't find anything. What is the
> correct way to do the following on Linux?
>
> @_silgen_name("foo")
> func foo(theInt: UInt)
> -> (a: UInt, b: UInt, c: UInt)
>
> var (d, e, f) = foo(aNum)
>
> Where foo is:
>
> typedef struct {
> long a;
> long b;
> long c;
> } Tuple;
>
> extern "C" {
> Tuple foo(int i) {
> return Tuple{ i, i, i };
> }
> }
>
> Currently, the call to foo crashes because foo wants to return the tuple
> indirectly, but the Swift call expects the three scalar return values in
> registers. This example is a generalization of runtime functions such as
> swift_class_getInstanceExtents, which happens to work because it only returns
> two scalars in RAX and RDX, which is supported by Clang. But my tests show
> that three-scalar tuples/structs will cause problems. On architectures where
> Clang only supports one scalar return value, the problem is worse.
>
> Am I doing something wrong or is there already a way to deal with this (e.g.
> annotation in Swift code to make it obey C ABI, or vice versa)?
>
Don't use @_silgen_name. If you want to use a C API from Swift, define a Clang
module for its headers, and import the module. See
http://clang.llvm.org/docs/Modules.html for documentation on Clang module maps.
-Joe
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