rsync - Jan 2008 - DO NOT REPLY [Bug 5170] New: Cross compilation does not work

https://bugzilla.samba.org/show_bug.cgi?id=5170

           Summary: Cross compilation does not work
           Product: rsync
           Version: 3.0.0
          Platform: x86
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P3
         Component: core
        AssignedTo: wayned@samba.org
        ReportedBy: r.schwebel@pengutronix.de
         QAContact: rsync-qa@samba.org


The makefiles try to build the "mkrounding" tool with the
"host" compiler;
however, this file is being executed later in the build, so it has to be
compiled with the "build" compiler. Usually, autotoolized Makefiles
solve this
by using CC_FOR_BUILD and the related CFLAGS_FOR_BUILD and LDFLAGS_FOR_BUILD.

Error message, taken during a build for ARM here:

----------8<----------8<----------
arm-v4t-linux-gnueabi-gcc -std=gnu99 -g -O2 -DHAVE_CONFIG_H -Wall -W -I./popt
-L/some/path/sysroot/arm-v4t-linux-gnueabi/lib
-L/some/path/sysroot/arm-v4t-linux-gnueabi/usr/lib -Wl,-rpath-link
-Wl,/some/path/sysroot/arm-v4t-linux-gnueabi/usr/lib -o mkrounding -I.
./mkrounding.c
./mkrounding >rounding.h
/bin/sh: ./mkrounding: cannot execute binary file
----------8<----------8<----------

Patch follows soon.


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------- Comment #1 from r.schwebel@pengutronix.de  2008-01-01 07:33 CST -------
Created an attachment (id=3083)
 --> (https://bugzilla.samba.org/attachment.cgi?id=3083&action=view)
[PATCH] Fix cross compilation, build mkrounding with CC_FOR_BUILD


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------- Comment #2 from matt@mattmccutchen.net  2008-01-01 09:14 CST -------
That is not the right fix.  Running "mkrounding" is meant to give
information
about how the *cross compiler* aligns structures so rsync can adapt
accordingly; building and running "mkrounding" for the build machine
may give
the wrong answer.

For cross compilation to work, we would need to find a way to get this
information from the cross compiler itself without running an executable that
it produces.  There is also the issue of the 11 configure tests that run things
on the build machine (assumed to be the target machine).


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------- Comment #3 from vapier@gentoo.org  2008-01-01 10:33 CST -------
autotools has a way of figuring out sizeof() by only cross-compiling by using
array indexes ... i bet that could be adapted to do offsetof() which is what
you're after, right ?


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wayned@samba.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED




------- Comment #4 from wayned@samba.org  2008-01-01 11:09 CST -------
I changed the makefile to output instructions for manually running mkrounding
on the target machine when cross-compiling.

If someone wishes to automate a cross-compiler build, they should determine the
rounding information (perhaps manually) and add their own build command (e.g.
an echo) to create the rounding.h file before running "make" (or
perhaps as a
patch to Makefile.in).  The result of the mkrounding command is a simple
define, such as this one:

#define EXTRA_ROUNDING 0


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------- Comment #5 from r.schwebel@pengutronix.de  2008-01-01 11:18 CST -------
(In reply to comment #4)
> I changed the makefile to output instructions for manually running
mkrounding
> on the target machine when cross-compiling.
Can you elaborate what mkrounding.c tries to achieve? It compares the size of n
'union file_extra's plus one 'struct file_struct' to the size of
a struct
containing these all and checks if it is equal for n = 1, 2 or 4. But what's
the
rationale behind this?

Maybe we find a better solution than throwing the file in manually (even
overwriting the test on the commandline with some ac_cv_* variable would be
better).


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------- Comment #6 from wayned@samba.org  2008-01-01 11:30 CST -------
Rsync has to determine the proper alignment for its internal struct when it
manually aligns it after a leading array.  If this can be determined at
configure time, that would obviously be preferable.


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------- Comment #7 from wayned@samba.org  2008-01-01 12:26 CST -------
OK, I took a clue from the configure sizeof check and changed the makefile to
try one or more compilations of mkrounding.c with different rounding sizes. 
This allows it to determine rounding without ever running the mkrounding
program.


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------- Comment #8 from matt@mattmccutchen.net  2008-01-01 12:31 CST -------
Cool!  It might be more natural to do the tests in the configure script.


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