what is the purpose of different cross compilers in AOSP?

[Ramprakash Jelari]

AOSP prebuilts directory contains the below.

./gcc/linux-x86/arm/arm-eabi-4.6/bin/arm-eabi-gcc
./gcc/linux-x86/arm/arm-linux-androideabi-4.6/bin/arm-linux-androideabi-gcc
./gcc/linux-x86/host/x86_64-linux-glibc2.7-4.6/bin/x86_64-linux-gcc
./gcc/linux-x86/host/i686-linux-glibc2.7-4.6/bin/i686-linux-gcc

my understanding: Correct me if i m wrong?

 i686-linux-gcc    -> compiler that compiles for x86 - 32 bit target.
 86_64-linux-gcc   -> compiler that compiles for x86 - 64 bit target.
 arm-linux-androideabi-gcc  -> ?
 arm-eabi-gcc               ->  ?  

[Dave Turvene]

On Friday, March 28, 2014 5:23:45 AM UTC-4, Ramprakash Jelari wrote:

my understanding: Correct me if i m wrong?

 i686-linux-gcc    -> compiler that compiles for x86 - 32 bit target.
 86_64-linux-gcc   -> compiler that compiles for x86 - 64 bit target.
 arm-linux-androideabi-gcc  -> ?
 arm-eabi-gcc               ->  ?  

You're sort of right.  The linux host compilers are native: building on linux x86 and running on linux x86.  So target and host are the same architecture.  The ARM compilers are cross-compilers: building on linux x86 and running on ARM processors.  So the target is ARM architecture (of which there are 7+ distinctive processor families) and the host is, again, linux x86.

On top of that the AOSP also uses LLVM/Clang to build libraries to run the renderscript code on the target.  Effectively, one is cross-compiling a set of compiler libraries to run natively on ARM, if that makes any sense.

[Ramprakash Jelari]

Thanks for the reply. I understood the below is for arm target building on x86 host.  What is the difference then between these two below compilers?

arm-linux-androideabi-gcc  and  arm-eabi-gcc 

[Jean-Baptiste Queru]

IIRC, one is for the kernel and the other for user-space, since those use slightly different ABIs. I might be wrong.

JBQ

--

Jean-Baptiste M. "JBQ" Quéru
Architect, Mobile, Yahoo

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[Dave Turvene]

On Tuesday, April 1, 2014 12:32:42 PM UTC-4, JBQ wrote:

IIRC, one is for the kernel and the other for user-space, since those use slightly different ABIs. I might be wrong.

JBQ

JBQ would know from his google days.  

I never thought about the different toolchains to tell you the truth.  I build the grouper kernel (I need DLKM support) and the AOSP using the arm-linux-androideabi-4.7 toolchain and everything runs fine.  BUT! http://source.android.com/source/building-kernels.html shows cloning an arm-eabi-4.6 toolchain.  

Still, it seems a little counter-intuitive to put the kernel tree in a different repo with instructions on how to clone the necessary toolchain but then include the kernel toolchain in the AOSP repo.

I just did a dumpspec on the two compilers.  There androideabi one has mno-android and tno-android variables.  The arm-eabi builds for more ARM architectures.  So maybe I was just lucky to have a google product.