Merge pull request #20 from ChrisDenton/comdat

Add an optional COMDAT record for the `.idata$3` section

Author: bjorn3

src/coff_import_file.rs

@@ -10,12 +10,13 @@ use std::path::PathBuf;
 use std::str::from_utf8;
 
 use object::pe::{
-    ImageFileHeader, ImageImportDescriptor, ImageRelocation, ImageSectionHeader, ImageSymbol,
-    ImportObjectHeader, IMAGE_FILE_32BIT_MACHINE, IMAGE_REL_AMD64_ADDR32NB,
-    IMAGE_REL_ARM64_ADDR32NB, IMAGE_REL_ARM_ADDR32NB, IMAGE_REL_I386_DIR32NB,
-    IMAGE_SCN_ALIGN_2BYTES, IMAGE_SCN_ALIGN_4BYTES, IMAGE_SCN_ALIGN_8BYTES,
-    IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_LNK_INFO, IMAGE_SCN_LNK_REMOVE, IMAGE_SCN_MEM_READ,
-    IMAGE_SCN_MEM_WRITE, IMAGE_SYM_CLASS_EXTERNAL, IMAGE_SYM_CLASS_NULL, IMAGE_SYM_CLASS_SECTION,
+    ImageAuxSymbolSection, ImageFileHeader, ImageImportDescriptor, ImageRelocation,
+    ImageSectionHeader, ImageSymbol, ImportObjectHeader, IMAGE_COMDAT_SELECT_ANY,
+    IMAGE_FILE_32BIT_MACHINE, IMAGE_REL_AMD64_ADDR32NB, IMAGE_REL_ARM64_ADDR32NB,
+    IMAGE_REL_ARM_ADDR32NB, IMAGE_REL_I386_DIR32NB, IMAGE_SCN_ALIGN_2BYTES, IMAGE_SCN_ALIGN_4BYTES,
+    IMAGE_SCN_ALIGN_8BYTES, IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_LNK_COMDAT,
+    IMAGE_SCN_LNK_INFO, IMAGE_SCN_LNK_REMOVE, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE,
+    IMAGE_SYM_CLASS_EXTERNAL, IMAGE_SYM_CLASS_NULL, IMAGE_SYM_CLASS_SECTION,
     IMAGE_SYM_CLASS_STATIC, IMAGE_SYM_CLASS_WEAK_EXTERNAL, IMAGE_WEAK_EXTERN_SEARCH_ALIAS,
 };
 use object::pod::bytes_of;
@@ -463,11 +464,14 @@ impl<'a> ObjectFactory<'a> {
     /// Creates a NULL import descriptor.  This is a small object file whcih
     /// contains a NULL import descriptor.  It is used to terminate the imports
     /// from a specific DLL.
-    fn create_null_import_descriptor(&self) -> Result<NewArchiveMember<'_>> {
+    ///
+    /// If `comdat` is set to true, the NULL import descriptor's section (`.idata$3`) will be
+    /// turned into a COMDAT section.
+    fn create_null_import_descriptor(&self, comdat: bool) -> Result<NewArchiveMember<'_>> {
         let mut buffer = Vec::new();
 
         const NUMBER_OF_SECTIONS: usize = 1;
-        const NUMBER_OF_SYMBOLS: usize = 1;
+        let number_of_symbols = if comdat { 3 } else { 1 };
 
         // COFF Header
         let header = ImageFileHeader {
@@ -477,7 +481,7 @@ impl<'a> ObjectFactory<'a> {
             pointer_to_symbol_table: u32!((size_of::<ImageFileHeader>() + (NUMBER_OF_SECTIONS * size_of::<ImageSectionHeader>()) +
                 // .idata$3
                 size_of::<ImageImportDescriptor>()).try_into().unwrap()),
-            number_of_symbols: u32!(NUMBER_OF_SYMBOLS.try_into().unwrap()),
+            number_of_symbols: u32!(number_of_symbols.try_into().unwrap()),
             size_of_optional_header: u16!(0),
             characteristics: u16!(if self.is_64_bit() {
                 0
@@ -506,6 +510,7 @@ impl<'a> ObjectFactory<'a> {
                     | IMAGE_SCN_CNT_INITIALIZED_DATA
                     | IMAGE_SCN_MEM_READ
                     | IMAGE_SCN_MEM_WRITE
+                    | if comdat { IMAGE_SCN_LNK_COMDAT } else { 0 }
             ),
         }];
         buffer.write_all(bytes_of(&section_table))?;
@@ -521,16 +526,38 @@ impl<'a> ObjectFactory<'a> {
         buffer.write_all(bytes_of(&import_descriptor))?;
 
         // Symbol Table
-        let mut symbol_table: [_; NUMBER_OF_SYMBOLS] = [ImageSymbol {
+        if comdat {
+            let symbol = ImageSymbol {
+                name: *b".idata$3",
+                value: u32!(0),
+                section_number: u16!(1),
+                typ: u16!(0),
+                storage_class: IMAGE_SYM_CLASS_STATIC,
+                number_of_aux_symbols: 1,
+            };
+            let aux = ImageAuxSymbolSection {
+                length: u32!(size_of::<ImageImportDescriptor>().try_into().unwrap()),
+                number_of_relocations: u16!(0),
+                number_of_linenumbers: u16!(0),
+                check_sum: u32!(0),
+                selection: IMAGE_COMDAT_SELECT_ANY,
+                number: u16!(0),
+                reserved: 0,
+                high_number: u16!(0),
+            };
+            buffer.write_all(bytes_of(&symbol))?;
+            buffer.write_all(bytes_of(&aux))?;
+        }
+        let mut null_descriptor_symbol = ImageSymbol {
             name: [0; 8],
             value: u32!(0),
             section_number: u16!(1),
             typ: u16!(0),
             storage_class: IMAGE_SYM_CLASS_EXTERNAL,
             number_of_aux_symbols: 0,
-        }];
-        set_name_to_string_table_entry(&mut symbol_table[0], size_of::<u32>());
-        buffer.write_all(bytes_of(&symbol_table))?;
+        };
+        set_name_to_string_table_entry(&mut null_descriptor_symbol, size_of::<u32>());
+        buffer.write_all(bytes_of(&null_descriptor_symbol))?;
 
         // String Table
         write_string_table(&mut buffer, &[NULL_IMPORT_DESCRIPTOR_SYMBOL_NAME])?;
@@ -826,6 +853,7 @@ pub fn write_import_library<W: Write + Seek>(
     exports: &[COFFShortExport],
     machine: MachineTypes,
     mingw: bool,
+    comdat: bool,
 ) -> Result<()> {
     let native_machine = if machine == MachineTypes::ARM64EC {
         MachineTypes::ARM64
@@ -838,7 +866,7 @@ pub fn write_import_library<W: Write + Seek>(
 
     members.push(of.create_import_descriptor()?);
 
-    members.push(of.create_null_import_descriptor()?);
+    members.push(of.create_null_import_descriptor(comdat)?);
 
     members.push(of.create_null_thunk()?);
 

tests/import_library.rs

@@ -5,8 +5,10 @@ use std::process::Command;
 
 use ar_archive_writer::{ArchiveKind, COFFShortExport, MachineTypes};
 use common::{create_archive_with_ar_archive_writer, create_archive_with_llvm_ar};
+use object::coff::CoffHeader;
+use object::pe::ImageFileHeader;
 use object::read::archive::ArchiveFile;
-use object::{Architecture, SubArchitecture};
+use object::{bytes_of, Architecture, Object, SubArchitecture, U32Bytes};
 use pretty_assertions::assert_eq;
 
 mod common;
@@ -99,6 +101,7 @@ fn create_import_library_with_ar_archive_writer(
     temp_dir: &Path,
     machine_type: MachineTypes,
     mingw: bool,
+    comdat: bool,
 ) -> Vec<u8> {
     let mut output_bytes = Cursor::new(Vec::new());
     ar_archive_writer::write_import_library(
@@ -107,6 +110,7 @@ fn create_import_library_with_ar_archive_writer(
         &get_members(machine_type),
         machine_type,
         mingw,
+        comdat,
     )
     .unwrap();
 
@@ -129,7 +133,7 @@ fn compare_to_lib() {
         let temp_dir = common::create_tmp_dir("import_library_compare_to_lib");
 
         let archive_writer_bytes =
-            create_import_library_with_ar_archive_writer(&temp_dir, machine_type, false);
+            create_import_library_with_ar_archive_writer(&temp_dir, machine_type, false, false);
 
         let llvm_lib_bytes = {
             let machine_arg = match machine_type {
@@ -164,6 +168,11 @@ fn compare_to_lib() {
             llvm_lib_bytes, archive_writer_bytes,
             "Import library differs. Machine type: {machine_type:?}",
         );
+
+        compare_comdat(
+            &create_import_library_with_ar_archive_writer(&temp_dir, machine_type, false, true),
+            &llvm_lib_bytes,
+        );
     }
 }
 
@@ -178,7 +187,7 @@ fn compare_to_dlltool() {
         let temp_dir = common::create_tmp_dir("import_library_compare_to_dlltool");
 
         let archive_writer_bytes =
-            create_import_library_with_ar_archive_writer(&temp_dir, machine_type, true);
+            create_import_library_with_ar_archive_writer(&temp_dir, machine_type, true, false);
 
         let llvm_lib_bytes = {
             let machine_arg = match machine_type {
@@ -215,6 +224,11 @@ fn compare_to_dlltool() {
             llvm_lib_bytes, archive_writer_bytes,
             "Import library differs. Machine type: {machine_type:?}",
         );
+
+        compare_comdat(
+            &create_import_library_with_ar_archive_writer(&temp_dir, machine_type, true, true),
+            &llvm_lib_bytes,
+        );
     }
 }
 
@@ -237,10 +251,11 @@ fn wrap_in_archive() {
         let mut import_lib_bytes = Cursor::new(Vec::new());
         ar_archive_writer::write_import_library(
             &mut import_lib_bytes,
-            &temp_dir.join("MyLibrary.dll").to_string_lossy().to_string(),
+            &temp_dir.join("MyLibrary.dll").to_string_lossy(),
             &get_members(machine_type),
             machine_type,
             false,
+            false,
         )
         .unwrap();
         let import_lib_bytes = import_lib_bytes.into_inner();
@@ -281,3 +296,61 @@ fn wrap_in_archive() {
         );
     }
 }
+
+fn compare_comdat(archive_writer_bytes: &[u8], llvm_bytes: &[u8]) {
+    let archive_writer = ArchiveFile::parse(archive_writer_bytes).unwrap();
+    let llvm = ArchiveFile::parse(llvm_bytes).unwrap();
+
+    for (archive_member, llvm_member) in archive_writer.members().zip(llvm.members()) {
+        let archive_member = archive_member.unwrap();
+        let llvm_member = llvm_member.unwrap();
+
+        if archive_member.size() != llvm_member.size() {
+            // Ensure that the member header is the same except for the file size.
+            let mut llvm_file_header = *llvm_member.header().unwrap();
+            llvm_file_header.size = *b"163       ";
+            assert_eq!(
+                bytes_of(archive_member.header().unwrap()),
+                bytes_of(&llvm_file_header)
+            );
+
+            // Ensure that the LLVM generated object contains .idata$3
+            object::File::parse(llvm_member.data(llvm_bytes).unwrap())
+                .unwrap()
+                .section_by_name_bytes(b".idata$3")
+                .unwrap();
+
+            // Ensure the COFF file headers are the same except for the symbol count.
+            let llvm_data = llvm_member.data(llvm_bytes).unwrap();
+            let archive_data = archive_member.data(archive_writer_bytes).unwrap();
+            let mut offset = 0;
+            let mut header = *ImageFileHeader::parse(llvm_data, &mut offset).unwrap();
+            header.number_of_symbols = U32Bytes::from_bytes(3_u32.to_le_bytes());
+            assert_eq!(
+                &archive_data[..size_of::<ImageFileHeader>()],
+                bytes_of(&header)
+            );
+
+            // The rest of the object file will always be the same as `expected`
+            // for all import files no matter the platform.
+            let expected = [
+                46, 105, 100, 97, 116, 97, 36, 51, 0, 0, 0, 0, 0, 0, 0, 0, 20, 0, 0, 0, 60, 0, 0,
+                0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 64, 16, 48, 192, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+                0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 46, 105, 100, 97, 116, 97, 36, 51, 0, 0, 0, 0, 1,
+                0, 0, 0, 3, 1, 20, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0,
+                4, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 2, 0, 29, 0, 0, 0, 95, 95, 78, 85, 76, 76, 95,
+                73, 77, 80, 79, 82, 84, 95, 68, 69, 83, 67, 82, 73, 80, 84, 79, 82, 0,
+            ];
+            assert_eq!(&archive_data[size_of::<ImageFileHeader>()..], &expected);
+        } else {
+            assert_eq!(
+                bytes_of(archive_member.header().unwrap()),
+                bytes_of(llvm_member.header().unwrap())
+            );
+            assert_eq!(
+                archive_member.data(archive_writer_bytes).unwrap(),
+                llvm_member.data(llvm_bytes).unwrap()
+            );
+        }
+    }
+}