[CMake] CMake - overriding shared linker flags

[K Lakshman]

I might have used the term incorrectly. The context is that I am trying to build 
a shared library which, on running by its own will print the version info ie., 
the name of the shared library will be libmylib.so which can be used to link 
with and build other executables. But when run as a command libmylib.so will 
print some information. Whether you call this an executable or a shared object 
is immaterial. For instance, /lib/libc.so.6 behaves in a similar way. I was just 
trying to mimic that behavior in my library.


Lakshman.



----- Original Message ----
From: Hendrik Sattler <post at hendrik-sattler.de>
To: K Lakshman <maruthilakshman-cmake at yahoo.com>
Cc: cmake at cmake.org
Sent: Wed, 23 June, 2010 3:59:27 PM
Subject: Re: [CMake] CMake - overriding shared linker flags

Zitat von K Lakshman <maruthilakshman-cmake at yahoo.com>:
> I'm trying to build a shared library (gcc on Linux CentOS) with -pie  flag. If 
>I
> simply add the flag -pie to CMAKE_SHARED_LINKER_FLAGS "-Wl,-pie", the command
> that gets invoked looks like this:
> gcc -shared -Wl,-pie <rest of the command> -o libmylibrary.so
> 
> A shared library built like this is not runnable stand-alone (I get an error
> /usr/lib/libc.so: bad ELF interpreter: No such file or directory).  Where as if 
>I
> can get the shared library to be built using this command:
> gcc -Wl,-shared -Wl,-pie <rest of the command> -o libmylibrary.so
> 
> then that shared library seems to run fine stand alone. (The only difference
> betweent the two commands is that the -shared flags is passed to gcc in the
> first version and directly to the linker in the second version thus bypassing
> collect2).
> 
> How do I change the shared library build command to use -Wl,-shared  instead 
of
> -shared? Do I have to write a complete custom command or can I use  some 
tricks
> to simply change this part alone?


Does that actually make sense? To cite from gcc manpage:
-pie
    Produce a position independent executable on targets which support it. For 
predictable results, you must also specify the same set of options that were 
used to generate code (-fpie, -fPIE, or model suboptions) when you specify this 
option.

-shared
    Produce a shared object which can then be linked with other objects to form 
an executable. Not all systems support this option. For predictable results, you 
must also specify the same set of options that were used to generate code 
(-fpic, -fPIC, or model suboptions) when you specify this option.[1]

So, you should NOT use -pie for shared libraries (which are _already_ position 
independent) but only for static libraries and executables, if you really want 
that.
Additionally, you then use "gcc -pie", not "gcc -Wl,-pie".

HS