[COFF] Don't mark mingw .eh_frame sections writable

This improves compatibility with GCC produced object files, where
the .eh_frame sections are read only. With mixed flags for the
involved .eh_frame sections, LLD creates two separate .eh_frame
sections in the output binary, one for each flag combination,
while ld.bfd probably merges them.

The previous setup of flags can be traced back to SVN r79346.

Differential Revision: https://reviews.llvm.org/D55209

llvm-svn: 348177

lib/MC/MCObjectFileInfo.cpp

@@ -479,10 +479,10 @@ void MCObjectFileInfo::initELFMCObjectFileInfo(const Triple &T, bool Large) {
 }
 
 void MCObjectFileInfo::initCOFFMCObjectFileInfo(const Triple &T) {
-  EHFrameSection = Ctx->getCOFFSection(
-      ".eh_frame", COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
-                       COFF::IMAGE_SCN_MEM_READ | COFF::IMAGE_SCN_MEM_WRITE,
-      SectionKind::getData());
+  EHFrameSection =
+      Ctx->getCOFFSection(".eh_frame", COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
+                                           COFF::IMAGE_SCN_MEM_READ,
+                          SectionKind::getData());
 
   // Set the `IMAGE_SCN_MEM_16BIT` flag when compiling for thumb mode.  This is
   // used to indicate to the linker that the text segment contains thumb instructions

test/MC/COFF/eh-frame.s

@@ -12,3 +12,16 @@ _main:
 	.cfi_endproc
 
 // CHECK:    Name: .eh_frame
+// CHECK-NEXT:    VirtualSize:
+// CHECK-NEXT:    VirtualAddress:
+// CHECK-NEXT:    RawDataSize:
+// CHECK-NEXT:    PointerToRawData:
+// CHECK-NEXT:    PointerToRelocations:
+// CHECK-NEXT:    PointerToLineNumbers:
+// CHECK-NEXT:    RelocationCount:
+// CHECK-NEXT:    LineNumberCount:
+// CHECK-NEXT:    Characteristics [
+// CHECK-NEXT:      IMAGE_SCN_ALIGN_4BYTES
+// CHECK-NEXT:      IMAGE_SCN_CNT_INITIALIZED_DATA
+// CHECK-NEXT:      IMAGE_SCN_MEM_READ
+// CHECK-NEXT:    ]