[LLVMdev] Cross compiling to ARM using LLC {Help}

[Tim Northover]

Hi Najem,

> # generate LLVM-IR for dijkstra_large.c
> $gcc -S -flto -o dijkstra_large.bc -fplugin=${DRAGONEGG} dijkstra_large.c

Is your GCC configured as an arm-linux-gnueabihf compiler? If not,
it's almost certainly going to be getting ABI details wrong. I'm
slightly surprised that it affects argv, but it's certainly the first
thing to think about.

> # generate TARGET object file for dijkstra_large.bc
> $./llc -march=arm -mcpu=cortex-a9 dijkstra_large.bc -o dijkstra_large.o -filetype=obj -O3

If Dragonegg *is* generating for ARM then the "-march=arm" option to
llc should be unnecessary.

Also, GCC should probably have "-O3" as well, since llc is the backend
code generator and doesn't run the mid-end phases.

> # Generate executalbe using Target's toolchain
> $arm-linux-gcc -static dijkstra_large.o -o dijkstra_large

I've not seen an arm-linux-gcc before, so I'm slightly worried about
what ABI it's using (-gnu, -gnueabi or -gnueabihf).

> The second issue is that when I use "arm-linux-gnueabihf-gcc" cross compiler
> instead of the arm-linux-gcc I get the following error

> Also it would be nice if anyone can point me to a tutorial which shows how
> to build LLVM cross compiler using the clang.

That sounds like a very good idea. For a start there are far more
people here who know how to get clang to cooperate than DragonEgg
(I've never even built DragonEgg, for example). We've got a couple of
documents on that topic:

http://llvm.org/docs/HowToCrossCompileLLVM.html
http://clang.llvm.org/docs/CrossCompilation.html

They're not perfect by any means yet (still fairly new), but it'd be
great to hear your experiences trying to follow them so we can improve
things.

Cheers.

Tim.