Improving Cross compilation of Perl 5 - report for July/August
Mon, 03-Sep-2012 by
reneeb
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_Jess Robinson writes:_
(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 config.sh" 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:
<pre>
#include <stdio.h>
#$i_stdlib I_STDLIB
#ifdef I_STDLIB
#include <stdlib.h>
#endif
int PERL_INT_SIZE;
long PERL_LONG_SIZE;
short PERL_SHORT_SIZE;
int main()
{
exit(0);
}
EOCP
</pre>
Running nm gets us:
<pre> $ /usr/src/android/android-ndk-r8/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-nm -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</pre>
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 "<code>-Dusecrosscompile=arm-linux-androideabi-</code>" 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 libc.so, 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.
<pre>
[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 x-cross-compile
10.50 Update Configure with better cross-compiling support
=====
24.75 hours total
</pre>
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