Re: detecting non-PIC in shared lib on Darwin?

[Shantonu Sen <ssen at opendarwin dot org>]

Andrew is referring to the following:
[shantonu@macboo]$ cat foo.c
extern int a;
int foo(void) { return a; }
[shantonu@macboo]$ cat bar.c
int a = 1;
[shantonu@macboo]$ cc -mdynamic-no-pic -c foo.c -arch ppc
[shantonu@macboo]$ cc -mdynamic-no-pic -c bar.c -arch ppc
[shantonu@macboo]$ cc -dynamiclib -o libfoo.dylib foo.o bar.o -arch ppc
ld: foo.o has local relocation entries in non-writable section  
(__TEXT,__text)
/usr/bin/libtool: internal link edit command failed
[shantonu@macboo]$

Instead of going through stubs in the data segment, -mdynamic-no-pic  
puts relocations directly in the text segment on the assumption that  
the final linked image will be an executable at a fixed address and  
the relocations will be resolved to absolute addresses. If you do the  
same experiment with -arch ppc64, you will not get a static linker  
error, but instead the program will crash at runtime. Some may  
consider that a bug that should be reported to Apple.

I don't believe there's a general way of detecting non-dylib-safe  
object files, except trying to link it into a dylib and see if it  
fails (for ppc32)

Shantonu

On Apr 26, 2006, at 6:45 PM, Jack Howarth wrote:

> Andrew,
>     What on earth would make you think that the linker on Darwin would
> reject non-PIC code in linking a shared library. The linker on Linux
> doesn't do any such thing (hence the discussion on the Debian mailing
> list of adopting this as check on their builds).
>
> http://lists.debian.org/debian-gcc/2003/10/msg00115.html
>
>                              Jack