COFF: Set TLS table header field.

TLS table header field is supposed to have address and size of TLS table.
The linker doesn't have to understand what TLS table is. TLS table's name
is always "_tls_used", so if there's that symbol, the linker simply sets
that symbol's RVA to the header. The size of the TLS table is always 40 bytes.

llvm-svn: 241426

lld/COFF/Writer.cpp

@@ -415,6 +415,12 @@ void Writer::writeHeader() {
     Dir[EXCEPTION_TABLE].RelativeVirtualAddress = Sec->getRVA();
     Dir[EXCEPTION_TABLE].Size = Sec->getVirtualSize();
   }
+  if (Symbol *Sym = Symtab->find("_tls_used")) {
+    if (Defined *B = dyn_cast<Defined>(Sym->Body.load())) {
+      Dir[TLS_TABLE].RelativeVirtualAddress = B->getRVA();
+      Dir[TLS_TABLE].Size = 40;
+    }
+  }
 
   // Section table
   // Name field in the section table is 8 byte long. Longer names need

lld/test/COFF/tls.test

@@ -0,0 +1,43 @@
+# RUN: yaml2obj < %s > %t.obj
+# RUN: lld -flavor link2 /out:%t.exe /entry:main %t.obj
+# RUN: llvm-readobj -file-headers %t.exe | FileCheck %s
+
+# CHECK: TLSTableRVA: 0x1000
+# CHECK: TLSTableSize: 0x28
+
+---
+header:
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: []
+sections:
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       4
+    SectionData:     00000000
+symbols:
+  - Name:            .text
+    Value:           0
+    SectionNumber:   1
+    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
+      Selection:       IMAGE_COMDAT_SELECT_ANY
+  - Name:            main
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            _tls_used
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...