Ld complains: in function “_start”, undefined reference to “__libc_csu_fini” & “__libc_csu_init”

cgtkld

I'm compiled a GTK+ program using clang, rather than gcc. So far so good, except I can't have ld link correctly.

Original makefile called gcc to do the linking, like this:

gcc -g -O2 -export-dynamic -o my_application somefile.o another.o -pthread -lgnomeui-2 -lSM -lICE -lbonoboui-2 -lgnomevfs-2 -lgnomecanvas-2 -lgnome-2 -lpopt -lbonobo-2 -lbonobo-activation -lORBit-2 -lart_lgpl_2 -lgconf-2 -lglade-2.0 -lgtk-x11-2.0 -lgdk-x11-2.0 -latk-1.0 -lgio-2.0 -lpangoft2-1.0 -lpangocairo-1.0 -lgdk_pixbuf-2.0 -lcairo -lpango-1.0 -lfreetype -lfontconfig -lgobject-2.0 -lgmodule-2.0 -lgthread-2.0 -lrt -lglib-2.0 -lxml2 -pthread -lgstreamer-0.10 -lgobject-2.0 -lgmodule-2.0 -lxml2 -lgthread-2.0 -lrt -lglib-2.0

If I simply substitute gcc with clang in the above command, I get this warning from the latter:

clang: warning: argument unused during compilation: '-e xport-dynamic'

Problem is: clang doesn't recognize "-export-dynamic" as a linker option, so it doesn't pass it off to ld. This causes the references to external functions to be scrapped: when final binary is executed, neither the menu options nor the buttons react.

If I do final linking step with gcc the binary works perfectly (even though it was really compiled with clang and gcc only does the linking). Since I'm trying to completely replace gcc with clang in my machine, this is not acceptable.

So I tried this:

ld /usr/lib/crt1.o /usr/lib/crti.o /usr/lib/crtn.o -g -O2 -export-dynamic my_application somefile.o another.o -o -lgnomeui-2 -lSM -lICE -lbonoboui-2 -lgnomevfs-2 -lgnomecanvas-2 -lgnome-2 -lpopt -lbonobo-2 -lbonobo-activation -lORBit-2 -lart_lgpl_2 -lgconf-2 -lglade-2.0 -lgtk-x11-2.0 -lgdk-x11-2.0 -latk-1.0 -lgio-2.0 -lpangoft2-1.0 -lpangocairo-1.0 -lgdk_pixbuf-2.0 -lcairo -lpango-1.0 -lfreetype -lfontconfig -lgobject-2.0 -lgmodule-2.0 -lgthread-2.0 -lrt -lglib-2.0 -lxml2 -lgstreamer-0.10 -lgobject-2.0 -lgmodule-2.0 -lxml2 -lgthread-2.0 -lrt -lglib-2.0

By adding first 3 objects I avoid the "can't find _start" message. But then I get the aforementioned two complaints:

/usr/lib/crt1.o: In function _start:
(.text+0x12): undefined reference to __libc_csu_fini
/usr/lib/crt1.o: In function _start:
(.text+0x19): undefined reference to __libc_csu_init

I tried adding crtbegin.o and crtend.o at the list, even before crt1.o , to no avail. What is the linker's correct invocation?

(Post Edit): If nothing else works, is there a way to catch what exact parameters gcc is passing to ld when gcc is used for the linking?

Best Answer

gcc automatically adds language support libraries and objects to your supplied list for link. You have to add them yourself if you want to invoke ld directly. Taking an example from man ld, it could be

ld -o <output> /lib/crt0.o hello.o -lc

Try adding -lc, the symbol you need should be in it (at least on my system, it is).

Function pointers in C

Let's start with a basic function which we will be pointing to:

int addInt(int n, int m) {
    return n+m;
}

First thing, let's define a pointer to a function which receives 2 ints and returns an int:

int (*functionPtr)(int,int);

Now we can safely point to our function:

functionPtr = &addInt;

Now that we have a pointer to the function, let's use it:

int sum = (*functionPtr)(2, 3); // sum == 5

Passing the pointer to another function is basically the same:

int add2to3(int (*functionPtr)(int, int)) {
    return (*functionPtr)(2, 3);
}

We can use function pointers in return values as well (try to keep up, it gets messy):

// this is a function called functionFactory which receives parameter n
// and returns a pointer to another function which receives two ints
// and it returns another int
int (*functionFactory(int n))(int, int) {
    printf("Got parameter %d", n);
    int (*functionPtr)(int,int) = &addInt;
    return functionPtr;
}

But it's much nicer to use a typedef:

typedef int (*myFuncDef)(int, int);
// note that the typedef name is indeed myFuncDef

myFuncDef functionFactory(int n) {
    printf("Got parameter %d", n);
    myFuncDef functionPtr = &addInt;
    return functionPtr;
}

R – Glade and static linking

First of all linking gtk+ against an application statically is not supported. You are likely to run into a lot of hairy problems.

GtkBuilder needs to be able to dlopen your library, you need to make sure that all he symbols from the related libraries are also exported by your binary. On ELF systems you'll have to pass in the -export-dynamic/-Wl,-export-dynamic to the linker/gcc.

Best Answer

Related Solutions

How do function pointers in C work

Function pointers in C

R – Glade and static linking

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