Combine data/text sections: Pad all sections to 4-byte minimum alignment

Author: LagoLunatic

objdiff-core/src/obj/read.rs

@@ -17,7 +17,7 @@ use crate::{
         Symbol, SymbolFlag, SymbolKind,
         split_meta::{SPLITMETA_SECTION, SplitMeta},
     },
-    util::{read_u16, read_u32},
+    util::{align_data_slice_to_4, align_size_to_4, align_u64_to_4, read_u16, read_u32},
 };
 
 fn map_section_kind(section: &object::Section) -> SectionKind {
@@ -739,7 +739,9 @@ fn do_combine_sections(
         }
         offsets.push(current_offset);
         current_offset += section.size;
+        current_offset = align_u64_to_4(current_offset);
         data_size += section.data.len();
+        data_size = align_size_to_4(data_size);
         num_relocations += section.relocations.len();
     }
     if data_size > 0 {
@@ -754,6 +756,7 @@ fn do_combine_sections(
         let section = &mut sections[i];
         section.size = 0;
         data.append(&mut section.data.0);
+        align_data_slice_to_4(&mut data);
         section.relocations.iter_mut().for_each(|r| r.address += offset);
         relocations.append(&mut section.relocations);
         line_info.append(&mut section.line_info.iter().map(|(&a, &l)| (a + offset, l)).collect());

objdiff-core/src/obj/split_meta.rs

@@ -3,6 +3,10 @@ use alloc::{string::String, vec, vec::Vec};
 use anyhow::{Result, anyhow};
 use object::{Endian, ObjectSection, elf::SHT_NOTE};
 
+#[cfg(feature = "std")]
+use crate::util::align_data_to_4;
+use crate::util::align_size_to_4;
+
 pub const SPLITMETA_SECTION: &str = ".note.split";
 pub const SHT_SPLITMETA: u32 = SHT_NOTE;
 pub const ELF_NOTE_SPLIT: &[u8] = b"Split";
@@ -190,17 +194,6 @@ where E: Endian
     }
 }
 
-fn align_size_to_4(size: usize) -> usize { (size + 3) & !3 }
-
-#[cfg(feature = "std")]
-fn align_data_to_4<W: std::io::Write + ?Sized>(writer: &mut W, len: usize) -> std::io::Result<()> {
-    const ALIGN_BYTES: &[u8] = &[0; 4];
-    if len % 4 != 0 {
-        writer.write_all(&ALIGN_BYTES[..4 - len % 4])?;
-    }
-    Ok(())
-}
-
 // ELF note format:
 // Name Size | 4 bytes (integer)
 // Desc Size | 4 bytes (integer)

objdiff-core/src/util.rs

@@ -1,4 +1,4 @@
-use alloc::format;
+use alloc::{format, vec::Vec};
 use core::fmt;
 
 use anyhow::{Result, ensure};
@@ -39,3 +39,24 @@ pub fn read_u16(obj_file: &object::File, reader: &mut &[u8]) -> Result<u16> {
     *reader = &reader[2..];
     Ok(obj_file.endianness().read_u16(value))
 }
+
+pub fn align_size_to_4(size: usize) -> usize { (size + 3) & !3 }
+
+pub fn align_u64_to_4(size: u64) -> u64 { (size + 3) & !3 }
+
+#[cfg(feature = "std")]
+pub fn align_data_to_4<W: std::io::Write + ?Sized>(
+    writer: &mut W,
+    len: usize,
+) -> std::io::Result<()> {
+    const ALIGN_BYTES: &[u8] = &[0; 4];
+    if len % 4 != 0 {
+        writer.write_all(&ALIGN_BYTES[..4 - len % 4])?;
+    }
+    Ok(())
+}
+
+pub fn align_data_slice_to_4(data: &mut Vec<u8>) {
+    const ALIGN_BYTE: u8 = 0;
+    data.resize(align_size_to_4(data.len()), ALIGN_BYTE);
+}