Am not able to call C++ function pointers from inline assembly
It seems you got confused by the pointer indirections, which is
confounded by the implicit indirections made by the compiler.
Here:
extern &quot;C&quot;
void __attribute__ ((used, noinline)) call(func_ptr *ptr) {
    (*ptr)();
}

The parameter ptr is not a function pointer: it's a pointer to a
function pointer. You have to dereference it twice in order to get the
function: (**ptr)();. Note that the compiler implicitly dereferences a
function pointer if you call it like a function: that's why you get no
error by explicitly dereferencing the pointer only once. In the
generated assembly, the lines
ld  r30, X+
ld  r31, X

dereference ptr in order to get the address of the function to call.
You probably wanted to write
extern &quot;C&quot;
void __attribute__ ((used, noinline)) call(func_ptr ptr) {
    ptr();
}

And then use it as:
call(tasks[0]);

If you just call(tasks), the array identifier decays to pointer, and
the compiler handles this as a shortcut for call(&amp;tasks[0]);, which
turns out to be compatible with your initial implementation of call().
Now, in your inline assembly you have
lds r26, (tasks)
lds r27, (tasks + 1)

The assembly treats tasks as a symbol representing the address of
the tasks array. The linker replaces those symbols by the actual
address (0x0200). Those instructions read the RAM at this and the
following address. These slots of RAM hold the first item of the array,
namely &amp;func_a. So now you have this address in the X register pair.
No need to read RAM again: you can movw r30, r26 and do the indirect
jump. Or, better yet, load into Z to begin with:
lds r30, (tasks)
lds r31, (tasks + 1)
eijmp

See also Majenko's answer: here I am assuming EIND is somehow
correctly set up to begin with. On an Uno, you would just use ijmp
instead of eijmp and not worry about EIND.