[lldb-dev] Host::GetArchitecture and the default target triple

Greg Clayton gclayton at apple.com
Tue Aug 19 13:58:53 PDT 2014

> On Aug 19, 2014, at 1:52 PM, Zachary Turner <zturner at google.com> wrote:
> Looking over the apple code path for Host::GetArchitecture, I'm a little confused about why all this custom logic is needed.  What are the situations in which llvm::sys::getDefaultTargetTriple() will return something other than what we want?  Specifically, a concrete example might help illustrate the problem.
> I understand from the comment that it has something to do with being able to run 32 and 64-bit executables in the same operating system.  Isn't this the case everywhere?  I can run 32-bit executables on Windows x64 as well.  llvm::Triple has a function called get32BitArchVariant() that I thought returns a 32-bit triple for this case.  Does this not work for some Apple configuration?
> It seems like this logic should be able to be sunk into llvm::Triple somehow.  Conceptually speaking, it seems like there should be two cases:
> 64-bit:
> host_arch_64 = llvm::Triple::getDefaultTargetTriple()
> host_arch_32 = llvm::Triple::getDefaultTargetTriple().get32BitArchVariant()
> 32-bit
> host_arch_64 = <empty>
> host_arch_32 = llvm::Triple::getDefaultTargetTriple()
> Why doesn't this work?

I am not sure if this would work. At Apple we can have either:

x86_64h-apple-macosx or x86_64-apple-macosx for 64 bit enabled machines. Not sure which llvm::Triple::getDefaultTargetTriple() returns. I highly doubt it detects x86_64h, though I could be wrong.

i386-apple-macosx for 32 bit.

I am happy to switch over if llvm::Triple::getDefaultTargetTriple() properly detects x86_64h on Haswell enabled macs. I will let others comment on their systems (FreeBSD, linux, windows, MingGW).

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