[LTP] 回复：[PATCH v1] include/mk/env_post.mk: enable __ANDROID__ definition for Android build

[Sandeep Patil <sspatil@android.com>]

On Sat, Apr 13, 2019 at 12:15:18AM +0800, 阮正旺 wrote:
> 
> -------- Original Message --------
> From: Petr Vorel
> Sent: Fri, 12 Apr 2019 08:28:14 +0200
> To: 阮正旺
> Cc: Sandeep Patil, Ltp, Steve Muckle
> Subject: Re: [LTP] 回复：[PATCH v1] include/mk/env_post.mk : enable
> __ANDROID__ definition for Android build
> > Hi Zhengwang,
> > 
> > > > > According to [1] android toolchain (I guess both AOSP and NDK toolchain) define
> > > > > __ANDROID__. Which is what I'd expect.
> > > > > Grepping aosp only dnsmasq and swiftshader use -D__ANDROID__ (these are from
> > > > > externals). -DANDROID is use more times (e.g. some drivers in hardware - ril,
> > > > > qcom, libsensors and wpa_supplicant).
> > > > >   From my point of view, instead of -D__ANDROID__ or -DANDROID I'd prefer to to have
> > > > > proper #ifdef HAVE_FOO guarders made by autotools checks. As android is not the
> > > > > only minor libc. But I understand it's not always possible and we already use
> > > > > some #ifdef __ANDROID__ in library sources and headers, so ack from myself to
> > > > > help compilation outside AOSP and without NDK.
> > > > Actually I was wrong. 1) I was using NDK toolchain. I'd expect it'd generate
> > > > __ANDROID__, but I don't see it in the output. 2) Building for android with
> > > > distro toolchain doesn't make sense as it wouldn't have Bionic.
> > > 1) Did you build outside AOSP? If so,  I think it is reasonable since
> > Yes, with android NDK (for Bionic and special toolchain tweeks).
> > Then I use ANDROID=1
> > 
> > > whatever __ANDROID__ or ANDROID are defined by Android build system instead
> > > of toolchain. I also tried to build the external/* thing and found ANDROID
> > > was actually generated. In my test, ANDROID seems to be the more suitable
> > > one, but in fact we can not build ltp inside AOSP because there is no
> > > Android.mk in ltp (please correct me if I am wrong...),  so ANDROID is
> > Yes, inside AOSP you need to use Android fork [1] which uses usual Android.bp.
> > Therefore AOSP does not use our build system.
> > 
> > > meaningless to us here. Actually, this is why I think this patch is still
> > > useful, since __ANDROID__ is enough to distinguish what to compile if
> > > ANDROID=1 is set with make.
> > > 2) In the case of cross-compilation, I think it still makes sense, since we
> > > can use the same toolchain, such as clang,  and build parameters (the
> > > specify the include headers and libs, etc) as AOSP. This is what I am doing
> > > now, you can see my steps I posted in my previous reply. But in this case,
> > > we need to obviously set -D__ANDROID__ in CFLAGS. After that , the process
> > > should be similar as we launch a build inside AOSP.
> > I don't know much about android toolchain, but IMHO there are some other tweaks
> > in their build system (to comply changes in Bionic), so not sure if it's even
> > possible to avoid using NDK for out-of-aosp tree. See also [2]. But that's a
> > question for for Android devs.
> 
> According to also [2], the situation gets clear now. All android targets
> should get __ANDROID__ defined by the compiler, but ANDROID only means 'this
> is AOSP' and is only for Windows targets. In our case, __ANDROID__ should be
> preferred.

Correct, and the build can still be make ANDROID=1 which translates to
-D__ANDROID__.

JFYI, there have been occasions when we changed something in bionic as a
result of an LTP tests, so those fixes will be missing for someone who is
using ndk for testing and building LTP.

That being said, thats a fairly small subset and is manageable. We can catch
those in reviews / patches very easily.

I like the idea of being able to build ouf-of-aosp, so I'm going to give this
a try now and will report.

- ssp
> 
> 
> Regards,
> 
> Zhengwang
> 
> > 
> > > Regards,
> > > Zhengwang
> > Kind regards,
> > Petr
> > 
> > [1] https://android.googlesource.com/platform/external/ltp/
> > [2] https://groups.google.com/forum/#!topic/android-ndk/cf9_f1SLXls