llvm dev - Mar 2014 - [LLVMdev] Cross-compiling Compiler-RT builtins

I am attempting to port an operating system project to use Clang/LLVM
instead of GCC, but I'm having issues with Compiler-RT. Right now, the OS is
being cross-compiled on an x86_64 host targeting ARMv7a. I built the LLVM
toolchain according to the instructions, though I limited the supported
targets to arm, x86, and x86_64 to reduce compilation time. I'm finding that
compilation proceeds fine but fails at the linking stage due to missing
compiler builtins. When I examined the build log for the LLVM toolchain, I
found that Compiler-RT was only being built for x86_64. So, as a stopgap,
I've started linking against the existing cross-compiled libgcc to fill in
the gaps. However, I'm trying to find out what I need to do to cross-compile
Compiler-RT's builtins library for ARMv7 so I can use it to replace libgcc.
Any help here would be appreciated.

 

Thanks,

Kev Kitchens

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On 4 March 2014 04:00, Kev Kitchens <kitchens.sync at me.com>
wrote:
> I've started linking against the existing cross-compiled libgcc to fill
in
> the gaps. However, I'm trying to find out what I need to do to
cross-compile
> Compiler-RT's builtins library for ARMv7 so I can use it to replace
libgcc.
> Any help here would be appreciated.
Hi Kev,

Non-Darwin Compiler-RT support for ARMv7 is patchy. I've ran some
tests and found some bugs (that I have yet to investigate and report),
but I wouldn't replace it yet in production, and certainly not when
cross-compiling, as I don't know if it even works.

It could be just a matter of fixing the CMake/autoconf files, or it
could be some more work, but if you're just trying to use LLVM instead
of GCC, I'd go without RT for the moment.

cheers,
--renato

On 4 March 2014 04:00, Kev Kitchens <kitchens.sync at me.com>
wrote:
> I've started linking against the existing cross-compiled libgcc to fill
in
> the gaps. However, I'm trying to find out what I need to do to
cross-compile
> Compiler-RT's builtins library for ARMv7 so I can use it to replace
libgcc.
> Any help here would be appreciated.
Hi Kev,

Non-Darwin Compiler-RT support for ARMv7 is patchy. I've ran some
tests and found some bugs (that I have yet to investigate and report),
but I wouldn't replace it yet in production, and certainly not when
cross-compiling, as I don't know if it even works.

It could be just a matter of fixing the CMake/autoconf files, or it
could be some more work, but if you're just trying to use LLVM instead
of GCC, I'd go without RT for the moment.

cheers,
--renato

I've implemented something like this in Rust's fork of
compiler-rt<https://github.com/rust-lang/compiler-rt/commits/rust-2014-02-17-do-not-delete>.

Note that this can only be built via makefile, and, I suspect, my change
does not do a good job at figuring out appropriate gcc flags for each
platform, because I expect CFLAGS to be passed along from the parent
project's build script.
On the plus side, it seems to work on all platforms that Rust currently
supports (Linux, Windows, OSX, FreeBSD, Android), so Rust (almost) doesn't
need libgcc anymore.  ("almost" because there's still no
replacement for
stack unwinding routines).



On Mon, Mar 3, 2014 at 12:00 PM, Kev Kitchens <kitchens.sync at me.com>
wrote:
> I am attempting to port an operating system project to use Clang/LLVM
> instead of GCC, but I'm having issues with Compiler-RT. Right now, the
OS
> is being cross-compiled on an x86_64 host targeting ARMv7a. I built the
> LLVM toolchain according to the instructions, though I limited the
> supported targets to arm, x86, and x86_64 to reduce compilation time.
I'm
> finding that compilation proceeds fine but fails at the linking stage due
> to missing compiler builtins. When I examined the build log for the LLVM
> toolchain, I found that Compiler-RT was only being built for x86_64. So, as
> a stopgap, I've started linking against the existing cross-compiled
libgcc
> to fill in the gaps. However, I'm trying to find out what I need to do
to
> cross-compile Compiler-RT's builtins library for ARMv7 so I can use it
to
> replace libgcc. Any help here would be appreciated.
>
>
>
> Thanks,
>
> Kev Kitchens
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
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On 4 Mar 2014, at 09:14, Vadim Chugunov <vadimcn at gmail.com> wrote:
>   ("almost" because there's still no replacement for stack
unwinding routines).
And comments like this are why we should move the stack unwind routines from
libc++abi into libunwind...

David