cmd/link: apply R_DWARFFILEREF later

Apply R_DWARFFILEREF relocations later, along with other relocations, so that we don't modify symbols' contents before they are written to the output buffer. This is in preparation for mmap'ing input files read-only. Change-Id: I8e9ffb2f05acf8f198589b8770f277beb3847541 Reviewed-on: https://go-review.googlesource.com/c/go/+/170740 Run-TryBot: Cherry Zhang <[email protected]> TryBot-Result: Gobot Gobot <[email protected]> Reviewed-by: Austin Clements <[email protected]>
freeformz · Apr 19, 2019 · 15a31bd · 15a31bd
1 parent b2f94d3
commit 15a31bd
Show file tree

Hide file tree

Showing 2 changed files with 10 additions and 10 deletions.
diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
@@ -168,12 +168,6 @@ func relocsym(ctxt *Link, s *sym.Symbol) {
 		if r.Siz == 0 { // informational relocation - no work to do
 			continue
 		}
-		if r.Type == objabi.R_DWARFFILEREF {
-			// These should have been processed previously during
-			// line table writing.
-			Errorf(s, "orphan R_DWARFFILEREF reloc to %v", r.Sym.Name)
-			continue
-		}
 
 		// We need to be able to reference dynimport symbols when linking against
 		// shared libraries, and Solaris, Darwin and AIX need it always
@@ -490,6 +484,10 @@ func relocsym(ctxt *Link, s *sym.Symbol) {
 			// This isn't a real relocation so it must not update
 			// its offset value.
 			continue
+
+		case objabi.R_DWARFFILEREF:
+			// The final file index is saved in r.Add in dwarf.go:writelines.
+			o = r.Add
 		}
 
 		if r.Variant != sym.RV_NONE {

diff --git a/src/cmd/link/internal/ld/dwarf.go b/src/cmd/link/internal/ld/dwarf.go
@@ -1302,7 +1302,7 @@ func writelines(ctxt *Link, unit *compilationUnit, ls *sym.Symbol) {
 		ls.SetUint32(ctxt.Arch, headerLengthOffset, uint32(headerend-headerstart))
 	}
 
-	// Apply any R_DWARFFILEREF relocations, since we now know the
+	// Process any R_DWARFFILEREF relocations, since we now know the
 	// line table file indices for this compilation unit. Note that
 	// this loop visits only subprogram DIEs: if the compiler is
 	// changed to generate DW_AT_decl_file attributes for other
@@ -1315,8 +1315,6 @@ func writelines(ctxt *Link, unit *compilationUnit, ls *sym.Symbol) {
 			if r.Type != objabi.R_DWARFFILEREF {
 				continue
 			}
-			// Mark relocation as applied (signal to relocsym)
-			r.Done = true
 			idx, ok := fileNums[int(r.Sym.Value)]
 			if ok {
 				if int(int32(idx)) != idx {
@@ -1329,7 +1327,11 @@ func writelines(ctxt *Link, unit *compilationUnit, ls *sym.Symbol) {
 					Errorf(f, "bad R_DWARFFILEREF relocation offset %d + 4 would write past length %d", r.Off, len(s.P))
 					continue
 				}
-				ctxt.Arch.ByteOrder.PutUint32(f.P[r.Off:r.Off+4], uint32(idx))
+				if r.Add != 0 {
+					Errorf(f, "bad R_DWARFFILEREF relocation: addend not zero")
+				}
+				r.Sym.Attr |= sym.AttrReachable | sym.AttrNotInSymbolTable
+				r.Add = int64(idx) // record the index in r.Add, we'll apply it in the reloc phase.
 			} else {
 				_, found := missing[int(r.Sym.Value)]
 				if !found {