llvm dev - Apr 2010 - [LLVMdev] Using LLVM with clang for a homebrew kernel

Hi!

In the llvm-doc is the following:

Also, since many platforms define their ABIs in terms of C, and since 
LLVM is lower-level than C, front-ends currently must emit 
platform-specific IR in order to have the result conform to the platform 
ABI.

Can you give an example for this except system calls (which e.g. on 
windows use
a different calling convention)?
If you write your own operating system then how does llvm-IR depend on 
the ABI?

-Jochen

On Thursday 08 April 2010 08:27:20 Jochen Wilhelmy
wrote:
> Hi!
>
> In the llvm-doc is the following:
>
> Also, since many platforms define their ABIs in terms of C, and since
> LLVM is lower-level than C, front-ends currently must emit
> platform-specific IR in order to have the result conform to the platform
> ABI.
>
> Can you give an example for this except system calls (which e.g. on
> windows use
> a different calling convention)?
> If you write your own operating system then how does llvm-IR depend on
> the ABI?
varargs is the poster boy.  Right now llvm proper only has support for
some pieces of varargs translation on x86_64.  Frontends handle the bulk of 
the work.

I hope to add some more code in this area relatively soon.

Of course, anything having to do with Fortran is done completely by
the frontend as there is no standard ABI for that language.

                                  -Dave

It's no problem for me to write platform specific code. In fact I have to.
I also don't bother recompiling my code for another target platform.

The only thing I need is to select the target platform, LLVM should emit
binary code for.
I'm going to place my HAL (so all of the platform dependent stuff in terms
of code written in C(++) and ASM) in some static library that can be linked
with my kernel code, but that's just to put a line between those two layers
for me as a programmer.
The platform specific code is written in C++ and some Assembly. It's the
compiler's job to create correct C(++) code for the platform and mine to
create correct assembler code which conforms to the ABI of my platform.

Currently I don't have much code. It's just a small kernel with some
memory management and half of a scheduler.
I just wanted to play with LLVM a bit and thought about compiling this
code with LLVM instead of GCC. That's all.
I don't even want to use any LLVM Bitcode in it. I just want to use LLVM
as a compiler.

The only reason why I'm asking on this mailing list is that I didn't
find
any documentation about how to use LLVM as a standalone cross-compiler in
terms of "compile this code for ARM and put it into a mach-o file,
please."

Andreas

On Thu, 08 Apr 2010 15:27:20 +0200, Jochen Wilhelmy <j.wilhelmy at
arcor.de>
wrote:
> Hi!
> 
> In the llvm-doc is the following:
> 
> Also, since many platforms define their ABIs in terms of C, and since 
> LLVM is lower-level than C, front-ends currently must emit 
> platform-specific IR in order to have the result conform to the platform
> ABI.
> 
> Can you give an example for this except system calls (which e.g. on 
> windows use
> a different calling convention)?
> If you write your own operating system then how does llvm-IR depend on 
> the ABI?
> 
> -Jochen
> 
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