[LLD][COFF] Align import directory chunk. (#80014)

The loader can usually handle an unaligned import dir chunk, but It's not
optimal and it's not what MSVC link.exe does.

Windows refuses to load ARM64X binaries with unaligned import directory.
aarch64 and arm64ec imports are shared in such binaries as much as
possible. As long as they use the same set of functions from given import
directory, both the directory and import addresses chunk are just shared.
When used set of functions differs, ARM64X dynamic relocations are used
to modify import dir to point to different names and import addresses for
its EC view. I suspect that the loader expects some alignment on ARM64X
dynamic relocation offset and may not be the case when relocated import
dir is not aligned.

Author: cjacek

lld/COFF/DLL.cpp

@@ -110,7 +110,7 @@ class OrdinalOnlyChunk : public NonSectionChunk {
 // A chunk for the import descriptor table.
 class ImportDirectoryChunk : public NonSectionChunk {
 public:
-  explicit ImportDirectoryChunk(Chunk *n) : dllName(n) {}
+  explicit ImportDirectoryChunk(Chunk *n) : dllName(n) { setAlignment(4); }
   size_t getSize() const override { return sizeof(ImportDirectoryTableEntry); }
 
   void writeTo(uint8_t *buf) const override {

lld/test/COFF/imports.test

@@ -48,3 +48,8 @@ MERGE-NEXT:   Symbol: ExitProcess (0)
 MERGE-NEXT:   Symbol:  (50)
 MERGE-NEXT:   Symbol: MessageBoxA (1)
 MERGE-NEXT: }
+
+# Verify that import table is properly aligned.
+# RUN: llvm-readobj --headers %t.exe | FileCheck -check-prefix=IMPORTDIR %s
+IMPORTDIR:      ImportTableRVA: 0x1068
+IMPORTDIR-NEXT: ImportTableSize: 0x28

lld/test/COFF/pdb-publics-import.test

@@ -115,7 +115,7 @@ CHECK-NEXT:          characteristics =
 CHECK-NEXT:            initialized data
 CHECK-NEXT:            read permissions
 CHECK-NEXT: {{[0-9]+}} | S_COFFGROUP [size = 28] `.idata$2`
-CHECK-NEXT:          length = 40, addr = 0002:0061
+CHECK-NEXT:          length = 40, addr = 0002:0064
 CHECK-NEXT:          characteristics =
 CHECK-NEXT:            initialized data
 CHECK-NEXT:            read permissions
@@ -162,9 +162,9 @@ CHECK-NEXT:   SC[.rdata]  | mod = 3, 0002:0000, size = 28, data crc = 0, reloc c
 CHECK-NEXT:                 IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ
 CHECK-NEXT:   SC[.rdata]  | mod = 3, 0002:0028, size = 33, data crc = 0, reloc crc = 0
 CHECK-NEXT:                 IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ
-CHECK-NEXT:   SC[.rdata]  | mod = 3, 0002:0061, size = 20, data crc = 0, reloc crc = 0
+CHECK-NEXT:   SC[.rdata]  | mod = 3, 0002:0064, size = 20, data crc = 0, reloc crc = 0
 CHECK-NEXT:                 IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ
-CHECK-NEXT:   SC[.rdata]  | mod = 3, 0002:0081, size = 20, data crc = 0, reloc crc = 0
+CHECK-NEXT:   SC[.rdata]  | mod = 3, 0002:0084, size = 20, data crc = 0, reloc crc = 0
 CHECK-NEXT:                 IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ
 CHECK-NEXT:   SC[.rdata]  | mod = 3, 0002:0104, size = 8, data crc = 0, reloc crc = 0
 CHECK-NEXT:                 IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ