Add basic object parsing and a rough TODO list of steps

linker/src/lib.rs

@@ -1,4 +1,7 @@
-use clap::{App, AppSettings, Arg};
+use clap::{App, AppSettings, Arg, ArgMatches};
+use memmap2::Mmap;
+use object::Object;
+use std::fs;
 use std::io;
 
 pub const CMD_PREPROCESS: &str = "preprocess";
@@ -29,6 +32,46 @@ pub fn build_app<'a>() -> App<'a> {
         )
 }
 
-pub fn preprocess() -> io::Result<()> {
-    panic!("sad");
+pub fn preprocess(matches: &ArgMatches) -> io::Result<i32> {
+    let _app_functions = application_functions(&matches.value_of(SHARED_LIB).unwrap())?;
+
+    let exec_file = fs::File::open(&matches.value_of(EXEC).unwrap())?;
+    let exec_mmap = unsafe { Mmap::map(&exec_file)? };
+    let exec_obj = object::File::parse(&*exec_mmap).map_err(|err| {
+        io::Error::new(
+            io::ErrorKind::InvalidData,
+            format!("Failed to parse executable file: {}", err),
+        )
+    })?;
+
+    // TODO: Extract PLT related information for these functions.
+    // TODO: For all text sections check for function calls to app functions.
+    // TODO: Store all this data in a nice format.
+    // TODO: Potentially create a version of the executable with certain dynamic and PLT information deleted.
+    // It may be fine to just add some of this information to the metadata instead and deal with it on final exec creation.
+
+    Ok(0)
+}
+
+fn application_functions(shared_lib_name: &str) -> io::Result<Vec<String>> {
+    let shared_file = fs::File::open(&shared_lib_name)?;
+    let shared_mmap = unsafe { Mmap::map(&shared_file)? };
+    let shared_obj = object::File::parse(&*shared_mmap).map_err(|err| {
+        io::Error::new(
+            io::ErrorKind::InvalidData,
+            format!("Failed to parse shared library file: {}", err),
+        )
+    })?;
+    shared_obj
+        .exports()
+        .unwrap()
+        .into_iter()
+        .map(|export| String::from_utf8(export.name().to_vec()))
+        .collect::<Result<Vec<_>, _>>()
+        .map_err(|err| {
+            io::Error::new(
+                io::ErrorKind::InvalidData,
+                format!("Failed to load function names from shared library: {}", err),
+            )
+        })
 }