[llvm-objcopy] [COFF] Ignore associative sections in executables (llvm#151143)

COFF associative sections is a feature where relocatable object files
can have section snippets marked as related to another section snippet,
so they are kept or discarded in relation to that other section snippet.

When llvm-objcopy removes sections, it also removes sections that are
marked as associative to the removed section (as the associative
sections otherwise would end up orphaned).

In a linked executable module (EXE or DLL), section associativity is
meaningless - thus, we should ignore those fields from the input.

After linking, GNU ld keeps the SectionDefinition auxillary part of
symbols intact as it was in the source object file, which means that it
references section numbers in the source object files.

This fixes llvm#53433.

Author: mstorsjo

llvm/lib/ObjCopy/COFF/COFFReader.cpp

@@ -135,7 +135,7 @@ Error COFFReader::readSymbols(Object &Obj, bool IsBigObj) const {
     // it is, find the target section unique id.
     const coff_aux_section_definition *SD = SymRef.getSectionDefinition();
     const coff_aux_weak_external *WE = SymRef.getWeakExternal();
-    if (SD && SD->Selection == IMAGE_COMDAT_SELECT_ASSOCIATIVE) {
+    if (SD && SD->Selection == IMAGE_COMDAT_SELECT_ASSOCIATIVE && !Obj.IsPE) {
       int32_t Index = SD->getNumber(IsBigObj);
       if (Index <= 0 || static_cast<uint32_t>(Index - 1) >= Sections.size())
         return createStringError(object_error::parse_failed,

llvm/test/tools/llvm-objcopy/COFF/exe-bogus-assoc.test

@@ -0,0 +1,134 @@
+## Test that bogus associative section symbols in executables are ignored.
+##
+## The executable contains two (bogus) associative section symbols, both for
+## (parts of) the .rdata section; one pointing at the .debug_info section
+## (which will be stripped out) and one pointing at a nonexistent section.
+##
+## Check that stripping does succeed, and that it doesn't end up removing
+## the .rdata section.
+
+# RUN: yaml2obj %s -o %t.in.exe
+
+# RUN: llvm-strip --strip-debug %t.in.exe -o %t.out.exe
+# RUN: llvm-readobj --sections %t.out.exe | FileCheck %s
+
+# CHECK: Name: .rdata
+
+--- !COFF
+OptionalHeader:
+  AddressOfEntryPoint: 4096
+  ImageBase:       5368709120
+  SectionAlignment: 4096
+  FileAlignment:   512
+  MajorOperatingSystemVersion: 4
+  MinorOperatingSystemVersion: 0
+  MajorImageVersion: 0
+  MinorImageVersion: 0
+  MajorSubsystemVersion: 5
+  MinorSubsystemVersion: 2
+  Subsystem:       IMAGE_SUBSYSTEM_WINDOWS_CUI
+  DLLCharacteristics: [  ]
+  SizeOfStackReserve: 2097152
+  SizeOfStackCommit: 4096
+  SizeOfHeapReserve: 1048576
+  SizeOfHeapCommit: 4096
+header:
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: [  ]
+sections:
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    VirtualAddress:  4096
+    VirtualSize:     48
+    SectionData:     E806000000E802000000C3C3C30F1F00FFFFFFFFFFFFFFFF0000000000000000FFFFFFFFFFFFFFFF0000000000000000
+    SizeOfRawData:   512
+  - Name:            .rdata
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ ]
+    VirtualAddress:  8192
+    VirtualSize:     4
+    SectionData:     '00000000'
+    SizeOfRawData:   512
+  - Name:            .debug_info
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_DISCARDABLE, IMAGE_SCN_MEM_READ ]
+    VirtualAddress:  16384
+    VirtualSize:     4
+    SectionData:     '00000000'
+    SizeOfRawData:   512
+symbols:
+  - Name:            .text
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          11
+      NumberOfRelocations: 2
+      NumberOfLinenumbers: 0
+      CheckSum:        1703692295
+      Number:          1
+  - Name:            '.text$func1'
+    Value:           11
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          1
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        40735498
+      Number:          3
+      Selection:       IMAGE_COMDAT_SELECT_ANY
+  - Name:            .rdata
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          1
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          3
+      Selection:       IMAGE_COMDAT_SELECT_ASSOCIATIVE
+  - Name:            '.text$func2'
+    Value:           12
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          1
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        40735498
+      Number:          4
+      Selection:       IMAGE_COMDAT_SELECT_ANY
+  - Name:            .rdata
+    Value:           1
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          1
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          4
+      Selection:       IMAGE_COMDAT_SELECT_ASSOCIATIVE
+  - Name:            .debug_info
+    Value:           0
+    SectionNumber:   3
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          4
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          0
+...