From 36bb5ddcc67dabaf5d00d7335a9e764c4c668ee7 Mon Sep 17 00:00:00 2001
From: Luke Street <luke.street@encounterpc.com>
Date: Sun, 1 Oct 2023 12:50:21 -0400
Subject: [PATCH] Zero out section data for relocations in relocatable ELFs

Fixes issues with Wii versions of mwld.
---
 Cargo.lock      |  2 +-
 Cargo.toml      |  2 +-
 src/util/elf.rs | 41 +++++++++++++++++++++++++++++++++++++++--
 3 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index b589f57..5997702 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -331,7 +331,7 @@ dependencies = [
 
 [[package]]
 name = "decomp-toolkit"
-version = "0.5.4"
+version = "0.5.5"
 dependencies = [
  "anyhow",
  "ar",
diff --git a/Cargo.toml b/Cargo.toml
index 90d68ec..80ebb09 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,7 +3,7 @@ name = "decomp-toolkit"
 description = "Yet another GameCube/Wii decompilation toolkit."
 authors = ["Luke Street <luke@street.dev>"]
 license = "MIT OR Apache-2.0"
-version = "0.5.4"
+version = "0.5.5"
 edition = "2021"
 publish = false
 build = "build.rs"
diff --git a/src/util/elf.rs b/src/util/elf.rs
index 9f99c3f..fc772e5 100644
--- a/src/util/elf.rs
+++ b/src/util/elf.rs
@@ -13,7 +13,7 @@ use object::{
     elf,
     elf::{SHF_ALLOC, SHF_EXECINSTR, SHF_WRITE, SHT_NOBITS, SHT_PROGBITS},
     write::{
-        elf::{ProgramHeader, Rel, SectionHeader, SectionIndex, SymbolIndex},
+        elf::{ProgramHeader, Rel, SectionHeader, SectionIndex, SymbolIndex, Writer},
         StringId,
     },
     Architecture, Endianness, Object, ObjectKind, ObjectSection, ObjectSymbol, Relocation,
@@ -21,6 +21,7 @@ use object::{
 };
 
 use crate::{
+    array_ref,
     obj::{
         ObjArchitecture, ObjInfo, ObjKind, ObjReloc, ObjRelocKind, ObjSection, ObjSectionKind,
         ObjSplit, ObjSymbol, ObjSymbolFlagSet, ObjSymbolFlags, ObjSymbolKind, ObjUnit,
@@ -631,7 +632,11 @@ pub fn write_elf(obj: &ObjInfo) -> Result<Vec<u8>> {
         }
         writer.write_align(32);
         ensure!(writer.len() == out_section.offset);
-        writer.write(&section.data);
+        if obj.kind == ObjKind::Relocatable {
+            write_relocatable_section_data(&mut writer, section)?;
+        } else {
+            writer.write(&section.data);
+        }
     }
 
     for ((_, section), out_section) in obj.sections.iter().zip(&out_sections) {
@@ -876,3 +881,35 @@ fn to_obj_reloc(
     }?;
     Ok(Some(ObjReloc { kind: reloc_kind, target_symbol, addend, module: None }))
 }
+
+/// Writes section data while zeroing out relocations.
+fn write_relocatable_section_data(w: &mut Writer, section: &ObjSection) -> Result<()> {
+    ensure!(section.address == 0);
+    let mut current_address = 0;
+    for (addr, reloc) in section.relocations.iter() {
+        w.write(&section.data[current_address..addr as usize]);
+        let mut ins = u32::from_be_bytes(*array_ref!(section.data, addr as usize, 4));
+        match reloc.kind {
+            ObjRelocKind::Absolute => {
+                ins = 0;
+            }
+            ObjRelocKind::PpcAddr16Hi | ObjRelocKind::PpcAddr16Ha | ObjRelocKind::PpcAddr16Lo => {
+                ins &= !0xFFFF;
+            }
+            ObjRelocKind::PpcRel24 => {
+                ins &= !0x3FFFFFC;
+            }
+            ObjRelocKind::PpcRel14 => {
+                ins &= !0xFFFC;
+            }
+            ObjRelocKind::PpcEmbSda21 => {
+                ins &= !0x1FFFFF;
+            }
+        }
+        w.write(&ins.to_be_bytes());
+        current_address = addr as usize + 4;
+    }
+    // Write remaining data
+    w.write(&section.data[current_address..]);
+    Ok(())
+}