libgo patch committed: Fix handling of DW_FORM_strp for 64-bit DWARF

[Ian Lance Taylor]

This libgo patch fixes the handling of DW_FORM_strp when using 64-bit
DWARF.  This is an early backport of https://golang.org/cl/84379,
which will be in Go 1.11.
Backporting now for AIX support in gccgo.  Bootstrapped and ran Go
testsuite on x86_64-pc-linux-gnu.  Committed to mainline.

Ian

Index: gcc/go/gofrontend/MERGE
===================================================================
--- gcc/go/gofrontend/MERGE     (revision 256450)
+++ gcc/go/gofrontend/MERGE     (working copy)
@@ -1,4 +1,4 @@
-19d94969c5202c07b3b166079b9f4ebbb52dfa6b
+1176dd2b53f2d2b826b599a126f3f9828283cec3
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.
Index: libgo/go/debug/dwarf/entry.go
===================================================================
--- libgo/go/debug/dwarf/entry.go       (revision 256366)
+++ libgo/go/debug/dwarf/entry.go       (working copy)
@@ -461,7 +461,18 @@ func (b *buf) entry(atab abbrevTable, ub
                case formString:
                        val = b.string()
                case formStrp:
-                       off := b.uint32() // offset into .debug_str
+                       var off uint64 // offset into .debug_str
+                       is64, known := b.format.dwarf64()
+                       if !known {
+                               b.error("unknown size for DW_FORM_strp")
+                       } else if is64 {
+                               off = b.uint64()
+                       } else {
+                               off = uint64(b.uint32())
+                       }
+                       if uint64(int(off)) != off {
+                               b.error("DW_FORM_strp offset out of range")
+                       }
                        if b.err != nil {
                                return nil
                        }