Sam,
Since you seems very knowledgable why does the error desepear when I
initialize the structure ?
int bar [ 4 * 256 ] = { 0,1,2, ... };
I did not changed nor any compiler option, neither any declaration.
I still cannot see the difference in between those two, since the
declaration is exactly the same. The only difference being a default
initialization.
Thanks again for your time,
Mathieu
On Jun 6, 2005, at 5:57 PM, Sam Lauber wrote:
Hello,
I have a question about a valid C code. I am trying to compile
the following code in MacOSX (*). I don't understand what the
problem is ? Could someone please explain me what is going on ?
Since I declare the variable with extern I should not need to pass
-fno-common, right ?
Thanks for your help
Mathieu
foo.h:
extern int bar[];
foo.c:
int bar[4 * 256];
And compile lines are:
$ gcc -o foo.o -Wall -W -fPIC -c foo.c
$ gcc -dynamiclib -o libfoo.dylib foo.o
ld: common symbols not allowed with MH_DYLIB output format with the
-multi_module option
foo.o definition of common _bar (size 4096)
/usr/bin/libtool: internal link edit command failed
using gcc 3.3 20030304 (Apple Computer, Inc. build 1671)
This is not a problem with GCC. In fact, it is not a problem at all.
It is a
misunderstanding of the linker. When you run
gcc -dynamiclib -o libfoo.dylib foo.o
it really does
libtool -dynamic -o libfoo.dylib foo.o
which becomes
ld -dylib -o libfoo.dylib foo.o
However, -multi_module is the default, so it really is
ld -dylib -o libfoo.dylib foo.o -multi_module
-multi_module is enabled by default, so you can get errors from the
linker of
the form `libfoo.dylib(foo.o)' when there's a link problem.
The error happens because
a) an `extern' variable is called a `common variable'
b) in multipule module mode, common variables are not allowed
c) if they were allowed, it would defeat the purpose of that option:
better
diagnostics
To fix it, add -Wl,-single_module to the end of the GCC command line.
However, note that subsequent linker errors will refer to
`libfoo.dylib' instead
of `libfoo.dylib(foo.o)'.
Samuel Lauber
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