Combine data/text sections: Pad sections to more than 4-byte alignment if they have alignment specified

Author: LagoLunatic

objdiff-core/src/obj/mod.rs

@@ -109,6 +109,12 @@ impl Section {
         }
     }
 
+    // The alignment to use when "Combine data/text sections" is enabled.
+    pub fn combined_alignment(&self) -> u64 {
+        const MIN_ALIGNMENT: u64 = 4;
+        self.align.map(|align| align.get().max(MIN_ALIGNMENT)).unwrap_or(MIN_ALIGNMENT)
+    }
+
     pub fn relocation_at<'obj>(
         &'obj self,
         obj: &'obj Object,

objdiff-core/src/obj/read.rs

@@ -17,7 +17,7 @@ use crate::{
         Symbol, SymbolFlag, SymbolKind,
         split_meta::{SPLITMETA_SECTION, SplitMeta},
     },
-    util::{align_data_slice_to_4, align_size_to_4, align_u64_to_4, read_u16, read_u32},
+    util::{align_data_slice_to, align_u64_to, read_u16, read_u32},
 };
 
 fn map_section_kind(section: &object::Section) -> SectionKind {
@@ -740,9 +740,10 @@ fn do_combine_sections(
         }
         offsets.push(current_offset);
         current_offset += section.size;
-        current_offset = align_u64_to_4(current_offset);
+        let align = section.combined_alignment();
+        current_offset = align_u64_to(current_offset, align);
         data_size += section.data.len();
-        data_size = align_size_to_4(data_size);
+        data_size = align_u64_to(data_size as u64, align) as usize;
         num_relocations += section.relocations.len();
     }
     if data_size > 0 {
@@ -757,7 +758,7 @@ 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);
+        align_data_slice_to(&mut data, section.combined_alignment());
         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/util.rs

@@ -42,8 +42,6 @@ pub fn read_u16(obj_file: &object::File, reader: &mut &[u8]) -> Result<u16> {
 
 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,
@@ -56,7 +54,9 @@ pub fn align_data_to_4<W: std::io::Write + ?Sized>(
     Ok(())
 }
 
-pub fn align_data_slice_to_4(data: &mut Vec<u8>) {
+pub fn align_u64_to(len: u64, align: u64) -> u64 { len + ((align - (len % align)) % align) }
+
+pub fn align_data_slice_to(data: &mut Vec<u8>, align: u64) {
     const ALIGN_BYTE: u8 = 0;
-    data.resize(align_size_to_4(data.len()), ALIGN_BYTE);
+    data.resize(align_u64_to(data.len() as u64, align) as usize, ALIGN_BYTE);
 }

objdiff-core/tests/snapshots/arch_x86__read_x86_combine_sections.snap

@@ -747,10 +747,10 @@ expression: obj.sections
         id: ".text-combined",
         name: ".text",
         address: 0,
-        size: 280,
+        size: 320,
         kind: Code,
         data: SectionData(
-            280,
+            320,
         ),
         flags: FlagSet(Combined),
         align: Some(
@@ -777,119 +777,119 @@ expression: obj.sections
                 flags: Coff(
                     20,
                 ),
-                address: 31,
+                address: 43,
                 target_symbol: 60,
                 addend: 0,
             },
             Relocation {
                 flags: Coff(
                     20,
                 ),
-                address: 50,
+                address: 62,
                 target_symbol: 52,
                 addend: 0,
             },
             Relocation {
                 flags: Coff(
                     20,
                 ),
-                address: 72,
+                address: 84,
                 target_symbol: 11,
                 addend: 0,
             },
             Relocation {
                 flags: Coff(
                     6,
                 ),
-                address: 88,
+                address: 100,
                 target_symbol: 64,
                 addend: 0,
             },
             Relocation {
                 flags: Coff(
                     6,
                 ),
-                address: 108,
+                address: 124,
                 target_symbol: 66,
                 addend: 0,
             },
             Relocation {
                 flags: Coff(
                     6,
                 ),
-                address: 128,
+                address: 156,
                 target_symbol: 6,
                 addend: 0,
             },
             Relocation {
                 flags: Coff(
                     6,
                 ),
-                address: 138,
+                address: 166,
                 target_symbol: 8,
                 addend: 0,
             },
             Relocation {
                 flags: Coff(
                     20,
                 ),
-                address: 149,
+                address: 177,
                 target_symbol: 57,
                 addend: 0,
             },
             Relocation {
                 flags: Coff(
                     20,
                 ),
-                address: 157,
+                address: 185,
                 target_symbol: 54,
                 addend: 0,
             },
             Relocation {
                 flags: Coff(
                     20,
                 ),
-                address: 179,
+                address: 219,
                 target_symbol: 54,
                 addend: 0,
             },
             Relocation {
                 flags: Coff(
                     20,
                 ),
-                address: 198,
+                address: 238,
                 target_symbol: 52,
                 addend: 0,
             },
             Relocation {
                 flags: Coff(
                     20,
                 ),
-                address: 227,
+                address: 267,
                 target_symbol: 57,
                 addend: 0,
             },
             Relocation {
                 flags: Coff(
                     20,
                 ),
-                address: 246,
+                address: 286,
                 target_symbol: 52,
                 addend: 0,
             },
             Relocation {
                 flags: Coff(
                     6,
                 ),
-                address: 268,
+                address: 308,
                 target_symbol: 68,
                 addend: 0,
             },
             Relocation {
                 flags: Coff(
                     20,
                 ),
-                address: 273,
+                address: 313,
                 target_symbol: 60,
                 addend: 0,
             },