[llvm-objcopy][COFF] Add support for extended relocation tables

[sdmitriev]

Summary

This patch adds support for COFF objects with extended relocation tables to the llvm-objcopy tool.

[mstorsjo]

The code looks good to me, but it would be good to have a testcase that actually covers the writing part of the patch. As far as I see, the testcase only checks that we don't error out if the extended relocations flag is set on input, but as the test object doesn't actually have that many relocations, it doesn't invoke that bit of the writer.

One can use gzipped object files (see COFF/bigobj.test for an example) for testcases where one needs a slightly larger test file.

[sdmitriev]

Added real object with extended relocations for LIT test.

[mstorsjo]

LGTM

[sdmitriev]

I think using generated object in the test is more preferable since yaml definition can be adjust if there would be a need for that, but it turned out that yaml2obj tool also has problems with COFF’s extended relocation tables. I have prepared a patch to fix this problem in the yaml2obj – D70251

I am going to commit this patch as is now and change it to use generated object once I commit D70251.

llvm/test/tools/llvm-objcopy/COFF/add-section.test

 # CHECK-ADD-EMPTY-NAME:      Characteristics [
 # CHECK-ADD-EMPTY-NAME-NEXT:   IMAGE_SCN_ALIGN_1BYTES
 # CHECK-ADD-EMPTY-NAME-NEXT:   IMAGE_SCN_CNT_INITIALIZED_DATA
 # CHECK-ADD-EMPTY-NAME-NEXT: ]
 # CHECK-ADD-EMPTY-NAME:      SectionData (
 # CHECK-ADD-EMPTY-NAME-NEXT:  0000: {{.+}}|DEADBEEF{{.+}}|
 # CHECK-ADD-EMPTY-NAME-NEXT: )
 
+## Test that llvm-objcopy can add a section to an object with extended
+## relocations.
+# RUN: %python %p/../Inputs/ungzip.py %p/Inputs/x86_64-xrelocs.obj.gz > %t.in.xrelocs.obj
+# RUN: llvm-objcopy --add-section=.test.section=%t.sec %t.in.xrelocs.obj %t1.xrelocs.obj
+# RUN: llvm-readobj --file-headers --sections --section-data %t1.xrelocs.obj | FileCheck %s --check-prefixes=CHECK-EXTENDED-RELOCS
+
+# CHECK-EXTENDED-RELOCS:      SectionCount: 5
+# CHECK-EXTENDED-RELOCS:      Name: .data
+# CHECK-EXTENDED-RELOCS-NEXT: VirtualSize:
+# CHECK-EXTENDED-RELOCS-NEXT: VirtualAddress:
+# CHECK-EXTENDED-RELOCS-NEXT: RawDataSize:
+# CHECK-EXTENDED-RELOCS-NEXT: PointerToRawData:
+# CHECK-EXTENDED-RELOCS-NEXT: PointerToRelocations:
+# CHECK-EXTENDED-RELOCS-NEXT: PointerToLineNumbers:
+# CHECK-EXTENDED-RELOCS-NEXT: RelocationCount: 65535
+# CHECK-EXTENDED-RELOCS-NEXT: LineNumberCount: 0
+# CHECK-EXTENDED-RELOCS-NEXT: Characteristics [
+# CHECK-EXTENDED-RELOCS-NEXT:   IMAGE_SCN_ALIGN_16BYTES
+# CHECK-EXTENDED-RELOCS-NEXT:   IMAGE_SCN_CNT_INITIALIZED_DATA
+# CHECK-EXTENDED-RELOCS-NEXT:   IMAGE_SCN_LNK_NRELOC_OVFL
+# CHECK-EXTENDED-RELOCS-NEXT:   IMAGE_SCN_MEM_READ
+# CHECK-EXTENDED-RELOCS-NEXT:   IMAGE_SCN_MEM_WRITE
+# CHECK-EXTENDED-RELOCS-NEXT: ]
+# CHECK-EXTENDED-RELOCS:      Name: .test.section
+# CHECK-EXTENDED-RELOCS:      Characteristics [
+# CHECK-EXTENDED-RELOCS-NEXT:   IMAGE_SCN_ALIGN_1BYTES
+# CHECK-EXTENDED-RELOCS-NEXT:   IMAGE_SCN_CNT_INITIALIZED_DATA
+# CHECK-EXTENDED-RELOCS-NEXT: ]
+# CHECK-EXTENDED-RELOCS:      SectionData (
+# CHECK-EXTENDED-RELOCS-NEXT:  0000: {{.+}}|DEADBEEF{{.+}}|
+# CHECK-EXTENDED-RELOCS-NEXT: )
+
 ## Test that llvm-objcopy produces an error if the file with section contents
 ## to be added does not exist.
 # RUN: not llvm-objcopy --add-section=.another.section=%t2 %t %t3 2>&1 | FileCheck -DFILE1=%t -DFILE2=%t2 %s --check-prefixes=ERR1
 
 # ERR1: error: '[[FILE1]]': '[[FILE2]]': {{[Nn]}}o such file or directory
 
 ## Another negative test for invalid --add-sections command line argument.
 # RUN: not llvm-objcopy --add-section=.another.section %t %t3 2>&1 | FileCheck %s --check-prefixes=ERR2

llvm/tools/llvm-objcopy/COFF/Reader.cpp

Error COFFReader::readSections(Object &Obj) const {
   // Section indexing starts from 1.
   for (size_t I = 1, E = COFFObj.getNumberOfSections(); I <= E; I++) {
     const coff_section *Sec;
     if (auto EC = COFFObj.getSection(I, Sec))
       return errorCodeToError(EC);
     Sections.push_back(Section());
     Section &S = Sections.back();
     S.Header = *Sec;
+    S.Header.Characteristics &= ~COFF::IMAGE_SCN_LNK_NRELOC_OVFL;
     ArrayRef<uint8_t> Contents;
     if (Error E = COFFObj.getSectionContents(Sec, Contents))
       return E;
     S.setContentsRef(Contents);
     ArrayRef<coff_relocation> Relocs = COFFObj.getRelocations(Sec);
     for (const coff_relocation &R : Relocs)
       S.Relocs.push_back(R);
     if (Expected<StringRef> NameOrErr = COFFObj.getSectionName(Sec))
       S.Name = *NameOrErr;
     else
       return NameOrErr.takeError();
-    if (Sec->hasExtendedRelocations())
-      return createStringError(object_error::parse_failed,
-                               "extended relocations not supported yet");
   }
   Obj.addSections(Sections);
   return Error::success();
 }
 
 Error COFFReader::readSymbols(Object &Obj, bool IsBigObj) const {
   std::vector<Symbol> Symbols;
   Symbols.reserve(COFFObj.getRawNumberOfSymbols());

llvm/tools/llvm-objcopy/COFF/Writer.cpp

 }
 
 void COFFWriter::layoutSections() {
   for (auto &S : Obj.getMutableSections()) {
     if (S.Header.SizeOfRawData > 0)
       S.Header.PointerToRawData = FileSize;
     FileSize += S.Header.SizeOfRawData; // For executables, this is already
                                         // aligned to FileAlignment.
+    if (S.Relocs.size() >= 0xffff) {
+      S.Header.Characteristics |= COFF::IMAGE_SCN_LNK_NRELOC_OVFL;
+      S.Header.NumberOfRelocations = 0xffff;
+      S.Header.PointerToRelocations = FileSize;
+      FileSize += sizeof(coff_relocation);
+    } else {
       S.Header.NumberOfRelocations = S.Relocs.size();
-    S.Header.PointerToRelocations =
-        S.Header.NumberOfRelocations > 0 ? FileSize : 0;
+      S.Header.PointerToRelocations = S.Relocs.size() ? FileSize : 0;
+    }
+
     FileSize += S.Relocs.size() * sizeof(coff_relocation);
     FileSize = alignTo(FileSize, FileAlignment);
 
     if (S.Header.Characteristics & IMAGE_SCN_CNT_INITIALIZED_DATA)
       SizeOfInitializedData += S.Header.SizeOfRawData;
   }
 }
 
for (const auto &S : Obj.getSections()) {
     // For executable sections, pad the remainder of the raw data size with
     // 0xcc, which is int3 on x86.
     if ((S.Header.Characteristics & IMAGE_SCN_CNT_CODE) &&
         S.Header.SizeOfRawData > Contents.size())
       memset(Ptr + Contents.size(), 0xcc,
              S.Header.SizeOfRawData - Contents.size());
 
     Ptr += S.Header.SizeOfRawData;
+
+    if (S.Relocs.size() >= 0xffff) {
+      object::coff_relocation R;
+      R.VirtualAddress = S.Relocs.size() + 1;
+      R.SymbolTableIndex = 0;
+      R.Type = 0;
+      memcpy(Ptr, &R, sizeof(R));
+      Ptr += sizeof(R);
+    }
     for (const auto &R : S.Relocs) {
       memcpy(Ptr, &R.Reloc, sizeof(R.Reloc));
       Ptr += sizeof(R.Reloc);
     }
   }
 }
 
 template <class SymbolTy> void COFFWriter::writeSymbolStringTables() {