cmd/link: set .ctors COFF section to writable and aligned

Without setting these flags, LLVM's LLD ignores the .ctors section when
merging objects.

Updates #44250.
Updates #39326.
Updates #38755.
Updates #36439.
Updates #43800.

Change-Id: I8766104508f7acd832088a590ee7d68afa0d6065
Reviewed-on: https://go-review.googlesource.com/c/go/+/291633
Trust: Jason A. Donenfeld <[email protected]>
Run-TryBot: Jason A. Donenfeld <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>

Author: zx2c4

src/cmd/link/internal/ld/pe.go

@@ -66,6 +66,8 @@ const (
 	IMAGE_SCN_MEM_WRITE              = 0x80000000
 	IMAGE_SCN_MEM_DISCARDABLE        = 0x2000000
 	IMAGE_SCN_LNK_NRELOC_OVFL        = 0x1000000
+	IMAGE_SCN_ALIGN_4BYTES           = 0x300000
+	IMAGE_SCN_ALIGN_8BYTES           = 0x400000
 	IMAGE_SCN_ALIGN_32BYTES          = 0x600000
 )
 
@@ -478,20 +480,19 @@ func (f *peFile) addInitArray(ctxt *Link) *peSection {
 	// However, the entire Go runtime is initialized from just one function, so it is unlikely
 	// that this will need to grow in the future.
 	var size int
+	var alignment uint32
 	switch objabi.GOARCH {
 	default:
 		Exitf("peFile.addInitArray: unsupported GOARCH=%q\n", objabi.GOARCH)
-	case "386":
-		size = 4
-	case "amd64":
-		size = 8
-	case "arm":
+	case "386", "arm":
 		size = 4
-	case "arm64":
+		alignment = IMAGE_SCN_ALIGN_4BYTES
+	case "amd64", "arm64":
 		size = 8
+		alignment = IMAGE_SCN_ALIGN_8BYTES
 	}
 	sect := f.addSection(".ctors", size, size)
-	sect.characteristics = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ
+	sect.characteristics = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE | alignment
 	sect.sizeOfRawData = uint32(size)
 	ctxt.Out.SeekSet(int64(sect.pointerToRawData))
 	sect.checkOffset(ctxt.Out.Offset())