On 8 June 2012 11:42, David Nadlinger <code@klickverbot.at> wrote:

I'm currently working on a few codegen issues in LDC, where I'm not quite sure if I understood the intended ABI for extern(D) on x86_64 correctly:

- What is the exact specification for returning static arrays by value?

- What is the ABI for D vararg functions? (extern(D) void foo(…);)

- What was the reason of explicitly exposing __va_argsave_t instead of going for compiler magic in vararg functions? The latter is what we do in LDC (LLVM provides va_* intrinsics), and it seems to work fine. We obviously try to be compatible to DMD, but I don't quite see why we should move towards an (at least subjectively) worse design: With the DMD implementation, the API is different from C _and_ requires annoying special casing of code for x86_64. Sure, code that relied on directly manipulating the argument pointer on x86 obviously can't work, but a program just using va_start/va_arg/va_end should compile fine on either platform without changes. With DMD, it doesn't.

By the way, http://dlang.org/abi.html seems to be quite outdated, as it still mentions static arrays being passed by reference.

Also related to my current LDC pre-release work, name mangling on OS X: http://d.puremagic.com/issues/show_bug.cgi?id=8207

Thanks,
David
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