debug/elf: support 32-bit SPARC relocs

Patch by Rainer Orth.
    
    Reviewed-on: https://go-review.googlesource.com/67111

From-SVN: r253292

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-9a9d526a4c0a7f5b3635034b3e1dc3bbe6380dd2
+5989ef1cd0add98f107839759a5bc57f34354d39
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/debug/elf/file.go

@@ -600,6 +600,8 @@ func (f *File) applyRelocations(dst []byte, rels []byte) error {
 		return f.applyRelocationsMIPS64(dst, rels)
 	case f.Class == ELFCLASS64 && f.Machine == EM_S390:
 		return f.applyRelocationss390x(dst, rels)
+	case f.Class == ELFCLASS32 && (f.Machine == EM_SPARC || f.Machine == EM_SPARC32PLUS):
+		return f.applyRelocationsSPARC(dst, rels)
 	case f.Class == ELFCLASS64 && f.Machine == EM_SPARCV9:
 		return f.applyRelocationsSPARC64(dst, rels)
 	case f.Class == ELFCLASS64 && f.Machine == EM_ALPHA:
@@ -1006,6 +1008,46 @@ func (f *File) applyRelocationss390x(dst []byte, rels []byte) error {
 	return nil
 }
 
+func (f *File) applyRelocationsSPARC(dst []byte, rels []byte) error {
+	// 12 is the size of Rela32.
+	if len(rels)%12 != 0 {
+		return errors.New("length of relocation section is not a multiple of 12")
+	}
+
+	symbols, _, err := f.getSymbols(SHT_SYMTAB)
+	if err != nil {
+		return err
+	}
+
+	b := bytes.NewReader(rels)
+	var rela Rela32
+
+	for b.Len() > 0 {
+		binary.Read(b, f.ByteOrder, &rela)
+		symNo := rela.Info >> 32
+		t := R_SPARC(rela.Info & 0xff)
+
+		if symNo == 0 || symNo > uint32(len(symbols)) {
+			continue
+		}
+		sym := &symbols[symNo-1]
+		if SymType(sym.Info&0xf) != STT_SECTION {
+			// We don't handle non-section relocations for now.
+			continue
+		}
+
+		switch t {
+		case R_SPARC_32, R_SPARC_UA32:
+			if rela.Off+4 >= uint32(len(dst)) || rela.Addend < 0 {
+				continue
+			}
+			f.ByteOrder.PutUint32(dst[rela.Off:rela.Off+4], uint32(rela.Addend))
+		}
+	}
+
+	return nil
+}
+
 func (f *File) applyRelocationsSPARC64(dst []byte, rels []byte) error {
 	// 24 is the size of Rela64.
 	if len(rels)%24 != 0 {