cmd/link: set pe section and file alignment to 0 during external linking

This is what gcc does when it generates object files.
And it is easier to count everything, when it starts from 0.
Make go linker do the same.

gcc also does not output IMAGE_OPTIONAL_HEADER or
PE64_IMAGE_OPTIONAL_HEADER for object files.
Perhaps we should do the same, but not in this CL.

For #10776.

Change-Id: I9789c337648623b6cfaa7d18d1ac9cef32e180dc
Reviewed-on: https://go-review.googlesource.com/36974Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/link/internal/amd64/obj.go

@@ -152,7 +152,7 @@ func archinit(ctxt *ld.Link) {
 			*ld.FlagDataAddr = 0
 		}
 		if *ld.FlagRound == -1 {
-			*ld.FlagRound = ld.PESECTALIGN
+			*ld.FlagRound = int(ld.PESECTALIGN)
 		}
 	}
 

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

@@ -101,15 +101,17 @@ type IMAGE_EXPORT_DIRECTORY struct {
 
 const (
 	PEBASE = 0x00400000
+)
 
+var (
 	// SectionAlignment must be greater than or equal to FileAlignment.
 	// The default is the page size for the architecture.
-	PESECTALIGN = 0x1000
+	PESECTALIGN int64 = 0x1000
 
 	// FileAlignment should be a power of 2 between 512 and 64 K, inclusive.
 	// The default is 512. If the SectionAlignment is less than
 	// the architecture's page size, then FileAlignment must match SectionAlignment.
-	PEFILEALIGN = 2 << 8
+	PEFILEALIGN int64 = 2 << 8
 )
 
 const (
@@ -435,8 +437,17 @@ func Peinit(ctxt *Link) {
 		dd = oh.DataDirectory[:]
 	}
 
+	if Linkmode == LinkExternal {
+		PESECTALIGN = 0
+		PEFILEALIGN = 0
+	}
+
 	PEFILEHEADR = int32(Rnd(int64(len(dosstub)+binary.Size(&fh)+l+binary.Size(&sh)), PEFILEALIGN))
-	PESECTHEADR = int32(Rnd(int64(PEFILEHEADR), PESECTALIGN))
+	if Linkmode != LinkExternal {
+		PESECTHEADR = int32(Rnd(int64(PEFILEHEADR), PESECTALIGN))
+	} else {
+		PESECTHEADR = 0
+	}
 	nextsectoff = int(PESECTHEADR)
 	nextfileoff = int(PEFILEHEADR)
 
@@ -1218,10 +1229,10 @@ func Asmbpe(ctxt *Link) {
 	oh.BaseOfCode = t.VirtualAddress
 	oh64.ImageBase = PEBASE
 	oh.ImageBase = PEBASE
-	oh64.SectionAlignment = PESECTALIGN
-	oh.SectionAlignment = PESECTALIGN
-	oh64.FileAlignment = PEFILEALIGN
-	oh.FileAlignment = PEFILEALIGN
+	oh64.SectionAlignment = uint32(PESECTALIGN)
+	oh.SectionAlignment = uint32(PESECTALIGN)
+	oh64.FileAlignment = uint32(PEFILEALIGN)
+	oh.FileAlignment = uint32(PEFILEALIGN)
 	oh64.MajorOperatingSystemVersion = 4
 	oh.MajorOperatingSystemVersion = 4
 	oh64.MinorOperatingSystemVersion = 0

src/cmd/link/internal/x86/obj.go

@@ -144,7 +144,7 @@ func archinit(ctxt *ld.Link) {
 			*ld.FlagDataAddr = 0
 		}
 		if *ld.FlagRound == -1 {
-			*ld.FlagRound = ld.PESECTALIGN
+			*ld.FlagRound = int(ld.PESECTALIGN)
 		}
 	}