[Tutorial][Binaries] gdc for android

[Andrew Wiley]

On Mon, Feb 6, 2012 at 1:40 AM, Johannes Pfau <nospam at example.com> wrote:
> Am Mon, 6 Feb 2012 03:07:31 +0200
> schrieb Manu <turkeyman at gmail.com>:
>
>> On 6 February 2012 02:25, Manu <turkeyman at gmail.com> wrote:
>>
>> > On 6 February 2012 00:04, Johannes Pfau <nospam at example.com> wrote:
>> >
>> >> Am Sun, 5 Feb 2012 18:04:12 +0100
>> >> schrieb Johannes Pfau <nospam at example.com>:
>> >>
>> >> > I will probably need some more time to get this working...
>> >> >
>> >>
>> >> I have some good news:
>> >> http://www.mediafire.com/?107we120sh3xx
>> >>
>> >> I fixed that problem and then the whole build worked fine. I'll
>> >> post build instructions soon, but the binaries are ready. I only
>> >> did a simple gdc -c test.d to check the compiler, but it seems to
>> >> work.
>> >>
>> >> Linking against druntime fails, as it uses functions which are not
>> >> available on Android (backtrace, signal stuff).
>> >>
>> >> I also built a simple hello world on linux (printf, no runtime)
>> >> and ran it on my android phone, and it worked!
>> >>
>> >> In case you haven't used GDC without runtime before, a short
>> >> introduction:
>> >>
>> >> * use gdc -nophoboslib to make gdc not link against phobos (and
>> >> afaik, druntime)
>> >> * theres also -nostdlib in case you need it
>> >> * complex code may require -fno-section-anchors because of bug #120
>> >> * You'll get an error about a missing _Dmodule_ref symbol. That
>> >> symbol is used by module constructors and not generated by gdc if
>> >>  -nophoboslib was passed. As long as you don't run the module
>> >>  constructors, you can add a fake _Dmodule_ref in a .c file:
>> >>
>> >> ------------
>> >> void* _Dmodule_ref;
>> >> ------------
>> >>
>> >> * The compiler defines version(Android)
>> >>
>> >> Here's my hello world:
>> >> ------------
>> >> version(Android)
>> >> {
>> >>    pragma(msg, "Hello Android!");
>> >> }
>> >>
>> >> extern(C)
>> >> {
>> >>    int printf(in char* format, ...);
>> >> }
>> >>
>> >> extern(C) void main()
>> >> {
>> >>    printf("Hello, %s!\n".ptr, "Android".ptr);
>> >> }
>> >> ------------
>> >>
>> >> compile the _Dmodule_ref into hack.o, then use
>> >> gdc -nophoboslib hello.d hack.o
>> >>
>> >
>> > Amazing! You sir, are a genius!
>> > I'm gonna have to have some fun with that after work tomorrow :)
>> >
>> > I reckon this binary distro should be put on d-p-l somewhere
>> > obvious.
>> >
>>
>> I just tried with -mfpu=neon, which should allow GCC to generate neon
>> opcodes for the simd stuff, but it didn't seem to want to do that. In
>> fact it generates really horrible code where it CALLS an intrinsic
>> for each float in the vector...
>> Any idea why this wouldn't work out of the box?
>
> The android toolchain configures gcc with: += --with-float=soft
> --with-fpu=vfp --with-arch=armv5te
>
> I could try to build an optimized build, but then you'll have to tell
> me what processor you're using. Cortex A8?
>
> I'm not sure if you can override that at runtime. You could probably
> try:
> -mfloat-abi=hard -mcpu=cortex-a8 -march=armv7-a -mfpu=neon

Actually, if the Android default is to build against softfloat ABI,
you may be stuck with it. If Android doesn't require hardfloat to run
and doesn't let developers provide multiple binaries for different
platforms (which it might - I don't know), things get very hard.

Also, with NEON, one of the things you don't really hear until you
start working with these is that NEON isn't actually required in most
if not all of the ARM CPU specs. I've specifically dealt with the
Tegra 2, which is used in a lot of phones and has no NEON support even
though it's ARM Cortex-A9.