llvm dev - Mar 2016 - clang triple and clang target

Can someone explain what exactly a clang triple is (--triple option) and
what is the connection between triple and a target? I know there is an
article ( http://clang.llvm.org/docs/CrossCompilation.html) that show how
to cross compile code, but I'm not clear about is why I need to specify
triple, why I can't just say compile for a given target?

Any help is appreciated.

-- 
Rail Shafigulin
Software Engineer
Esencia Technologies
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On Fri, Mar 11, 2016 at 01:20:11PM -0800, Rail Shafigulin via llvm-dev
wrote:
> Can someone explain what exactly a clang triple is (--triple option) and
> what is the connection between triple and a target? I know there is an
> article ( http://clang.llvm.org/docs/CrossCompilation.html) that show how
> to cross compile code, but I'm not clear about is why I need to specify
> triple, why I can't just say compile for a given target?
I assume with target you mean the backend? Consider the x86 backend. It
supports 32bit and 64bit mode, with the GNU x32 ABI in between. There
are three different executable formats support (ELF, PE, MachO) with
different constraints. Some platforms require 32bit alignment of the
stack, others require 128bit alignment. The list goes on. The triple specifies
the combination of target, OS and potentially file format and sub-ABI.

Joerg

>
> I assume with target you mean the backend? Consider the x86 backend. It
> supports 32bit and 64bit mode, with the GNU x32 ABI in between. There
> are three different executable formats support (ELF, PE, MachO) with
> different constraints. Some platforms require 32bit alignment of the
> stack, others require 128bit alignment. The list goes on. The triple
> specifies
> the combination of target, OS and potentially file format and sub-ABI.
>
> Joerg
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
Thanks for the response. I was trying to generate assembly which would use
vector instructions. I need to see how they look, whether it is ARM, Mips
or X86. However for some reason clang would generate an error saying that a
given target does not exist. Here is the command line I used:

clang -S test.c -o test.sse2.x86-64.s --target=x86-unknown-linux-eabi
-mfloat-abi=hard -mcpu=x86-64 -mfpu=SSE2 -fslp-vectorize-aggressive
-fslp-vectorize-aggressive -fslp-vectorize -fvectorize
-fno-lax-vector-conversions

Here is the response I got:
clang: warning: argument unused during compilation: '-mfloat-abi=hard'
clang: warning: argument unused during compilation: '-mcpu=x86-64'
clang: warning: argument unused during compilation: '-mfpu=SSE2'
error: unknown target triple 'x86-unknown-linux-eabi', please use
-triple
or -arch


I tried every possible combination of --target I could think of but nothing
worked. Would you mind helping me out?
Any help is appreciated.

-- 
Rail Shafigulin
Software Engineer
Esencia Technologies
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