Add callbacks to ld.so version of Linker's function

It is fact that ld.so has libc statially linked into it.

Normally we wouldn't need ld.so functionality once the program is
finalyl loaded, but with the next few patches, we will have dlopen which
will reuse the same ld.so functionality.

The problem is that it seams that huge part of the code is possible not
referntially transparent. That is, it is not impossible that some of the
functions have internals states. So when using the struct Linker that is
initialized by ld.so's copy of libc. we must access it using the same
copy even if both copies are identical.
For example in dlopen if you do linker.load_library(..). That would
segfault because it is using the function from libc not ld.so

So I don't truly undestand why should this be needed, but after long
hours of being stuck I thought maybe.. maybe that is the issue and
indeed it turned out to be so.

src/ld_so/callbacks.rs

@@ -0,0 +1,53 @@
+use super::linker::{Linker, DSO};
+use alloc::boxed::Box;
+use goblin::error::Result;
+
+pub struct LinkerCallbacks {
+    pub unload: Box<dyn Fn(&mut Linker, usize)>,
+    pub load_library: Box<dyn Fn(&mut Linker, &str) -> Result<usize>>,
+    pub link:
+        Box<dyn Fn(&mut Linker, Option<&str>, Option<DSO>, Option<usize>) -> Result<Option<usize>>>,
+    pub get_sym: Box<dyn Fn(&Linker, &str, Option<usize>) -> Option<usize>>,
+    pub run_init: Box<dyn Fn(&Linker, Option<usize>) -> Result<()>>,
+    pub run_fini: Box<dyn Fn(&Linker, Option<usize>) -> Result<()>>,
+}
+
+impl LinkerCallbacks {
+    pub fn new() -> LinkerCallbacks {
+        LinkerCallbacks {
+            unload: Box::new(unload),
+            load_library: Box::new(load_library),
+            link: Box::new(link),
+            get_sym: Box::new(get_sym),
+            run_init: Box::new(run_init),
+            run_fini: Box::new(run_fini),
+        }
+    }
+}
+
+fn unload(linker: &mut Linker, libspace: usize) {
+    linker.unload(libspace)
+}
+
+fn load_library(linker: &mut Linker, name: &str) -> Result<usize> {
+    linker.load_library(name)
+}
+
+fn link(
+    linker: &mut Linker,
+    primary_opt: Option<&str>,
+    dso: Option<DSO>,
+    libspace: Option<usize>,
+) -> Result<Option<usize>> {
+    linker.link(primary_opt, dso, libspace)
+}
+
+fn get_sym(linker: &Linker, name: &str, libspace: Option<usize>) -> Option<usize> {
+    linker.get_sym(name, libspace)
+}
+fn run_init(linker: &Linker, libspace: Option<usize>) -> Result<()> {
+    linker.run_init(libspace)
+}
+fn run_fini(linker: &Linker, libspace: Option<usize>) -> Result<()> {
+    linker.run_fini(libspace)
+}

src/ld_so/mod.rs

@@ -5,12 +5,12 @@ use crate::start::Stack;
 pub const PAGE_SIZE: usize = 4096;
 
 mod access;
+pub mod callbacks;
 pub mod debug;
 mod library;
 pub mod linker;
 pub mod start;
 pub mod tcb;
-
 pub fn static_init(sp: &'static Stack) {
     let mut phdr_opt = None;
     let mut phent_opt = None;