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JROBINSON TPF grant report July/August

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Jess Robinson
August 27, 2012 04:03
JROBINSON TPF grant report July/August
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(Report up to Aug 26th anyway, I'll add anything I do in the last few days 
of August to the next one)

After a bit of a slow start (and thus the reason to merge July/August 
reports), I've gotten started on the actual work, and managed to tick off 
one of my tasks.

I eliminated my earlier use of the tool "agcc" from the code base. This 
was an external (and with non-compatible licence) tool designed to make 
using the cross-compiled gcc similar to a normal gcc. In the end it turned 
out to be more of a hinderance. Getting rid of it and using Android's 
suggestion for "--sysroot" as a gcc option means upgrading the NDK to the 
latest one is now simple. The SDK is now not required at all.

The last 2 weeks (Weeks #6/#7) I was at the Perl Reunification Summit, and 
then YAPC::EU, which were inspirational. I got started on the second task 
I have identified. To enable me to merge (or better, re-port) my original 
changes to blead, I have started with a fresh copy of blead and will 
add a piece at a time.

Expanding Configure is my current target. It already has a small piece of 
code to support cross-compiling, using -Dusecrosscompile, however this 
mostly skips all the parts it can't do, like compiling and then running 
various pieces of code for testing sizes of integers and similar. In order 
to enable us to have as small a piece of "canned" as possible, I 
am adding support for these things.

Currently I have it using `nm` (or rather the copy in the cross-compiler 
bin-utils) to find the size of the variables declared in the 'try.c' 
binary. When cross-compiling, this now looks like:

   #include <stdio.h>
   #$i_stdlib I_STDLIB
   #ifdef I_STDLIB
   #include <stdlib.h>

      int PERL_INT_SIZE;
      long PERL_LONG_SIZE;
      short PERL_SHORT_SIZE;

   int main()

Running nm gets us:

-p -t d -S  UU/try
   00037740 d _DYNAMIC
   00037940 d _GLOBAL_OFFSET_TABLE_
   00033612 A __exidx_end
   00037996 A _bss_end__
   00037724 T __FINI_ARRAY__
   00037960 A __bss_start__
   00037968 00000004 B __dso_handle
   00033612 A __exidx_start
   00037984 00000004 B PERL_LONG_SIZE
   00037988 00000004 B PERL_INT_SIZE
            U __libc_init
   00037992 00000002 B PERL_SHORT_SIZE
   00037732 D __CTOR_LIST__
   00037996 A __bss_end__
   00033552 T _start
   00037716 T __INIT_ARRAY__
   00037960 A __bss_start
   00033600 00000012 T main
   00037996 A __end__
   00037708 D __PREINIT_ARRAY__
   00037960 A _edata
   00037996 A _end
            U exit
   00037960 D __data_start

And we extract the values for the PERL_* variables. The same process is 
repeated for long longs, long doubles, pointers etc. Assuming 
cross-compile environments all use gcc and contain the bin-utils, this 
ought to be fairly portable.

To ensure the correct 'nm' (and also later 'ar') is used, I've added 
support to Configure to allow the binaries to be named differently. The 
cross-compiler 'nm' for the NDK is, for example, 
'arm-linux-androideabi-nm'. If "-Dusecrosscompile=arm-linux-androideabi-" 
is passed as a Configure argument, binaries will be discovered with that 
string as a prefix.

I've now started to add support for -Dsysroot. The name is taken from the 
gcc option mentioned earlier, and is similar to chroot, it specifies a 
logical root directory under which headers and libraries can be found. 
Various parts of the Configure script try to discover which libraries are 
available, and the location of the, using absolute paths. When 
cross-compiling, these are being found on the host system, instead of 
inside the toolchain for the cross-compiler. Adding sysroot support means 
the compiler's headers and libraries can now be located correctly. This is 
applicable to any system with its compiler located in its own chroot, or 
multiple toolchains / libraries installed.

[Hours] [Activity]

5.75     Admin - Tasks, Emails, Planning
6.50     Remove agcc from x-cross-compile branch
2.00     Update to latest Android NDK and verify working with 
10.50    Update Configure with better cross-compiling support

24.75 hours total

Jess Robinson

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