From 49d93e20ddb143f5539797a3b470041b387e687d Mon Sep 17 00:00:00 2001
From: Astro <astro@spaceboyz.net>
Date: Tue, 14 Jul 2020 01:30:11 +0200
Subject: [PATCH] dyld: add Image.rebind()

---
 src/libdyld/src/lib.rs   |  7 +++++++
 src/libdyld/src/reloc.rs | 24 ++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/src/libdyld/src/lib.rs b/src/libdyld/src/lib.rs
index 1396947..54a07dd 100644
--- a/src/libdyld/src/lib.rs
+++ b/src/libdyld/src/lib.rs
@@ -93,6 +93,7 @@ extern fn dl_unwind_find_exidx(pc: u32, len_ptr: *mut u32) -> u32 {
 
 pub struct Library {
     pub image: Image,
+    pub arch: Arch,
     dyn_section: DynamicSection,
 }
 
@@ -163,6 +164,11 @@ impl Library {
         Ok(self.strtab().get(offset..offset + size)
            .ok_or("cannot read symbol name")?)
     }
+
+    /// Rebind Rela by `name` to a new `addr`
+    pub fn rebind(&self, name: &[u8], addr: *const ()) -> Result<(), Error> {
+        reloc::rebind(self.arch, self, name, addr as Elf32_Word)
+    }
 }
 
 pub fn load(
@@ -235,6 +241,7 @@ pub fn load(
     debug!("Relocating {} rela, {} rel, {} pltrel",
            dyn_section.rela.len(), dyn_section.rel.len(), dyn_section.pltrel.len());
     let lib = Library {
+        arch,
         image,
         dyn_section
     };
diff --git a/src/libdyld/src/reloc.rs b/src/libdyld/src/reloc.rs
index 0c0cb7a..9200703 100644
--- a/src/libdyld/src/reloc.rs
+++ b/src/libdyld/src/reloc.rs
@@ -133,3 +133,27 @@ pub fn relocate<R: Relocatable>(
 
     lib.image.write(rel.offset(), value)
 }
+
+pub fn rebind(
+    arch: Arch, lib: &Library, name: &[u8], value: Elf32_Word
+) -> Result<(), Error> {
+    for rela in lib.pltrel() {
+        let rel_type = RelType::new(arch, rela.type_info())
+            .ok_or("unsupported relocation type")?;
+        match rel_type {
+            RelType::Lookup => {
+                let sym = lib.symtab().get(ELF32_R_SYM(rela.r_info) as usize)
+                    .ok_or("symbol out of bounds of symbol table")?;
+                let sym_name = lib.name_starting_at(sym.st_name as usize)?;
+
+                if sym_name == name {
+                    lib.image.write(rela.offset(), value)?
+                }
+            }
+            // No associated symbols for other relocation types.
+            _ => {}
+        }
+    }
+
+    Ok(())
+}