cmd/link: do not add duplicate symbols to Allsym

When building shared libraries, all symbols on Allsym are marked reachable.
What I didn't realize was that this includes the ".dup" symbols created when
"dupok" symbols are read from multiple package files. This breaks now because
deadcode makes some assumptions that fail for these ".dup" symbols, but in any
case was a bad idea -- I suspect this change makes libstd.so a bunch smaller,
but creating it was broken before this CL so I can't be sure.

This change simply stops adding these symbols to Allsym, which might make some
of the many iterations over Allsym the linker does a touch quicker, although
that's not the motivation here.

Add a test that no symbols called ".dup" makes it into the runtime shared
library.

Fixes #14841

Change-Id: I65dd6e88d150a770db2d01b75cfe5db5fd4f8d25
Reviewed-on: https://go-review.googlesource.com/20780
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/misc/cgo/testshared/shared_test.go b/misc/cgo/testshared/shared_test.go
index 86fb530167de0a88339fed2cc816383bef36f186..30b00d593013af251b17958b736f00714015f329 100644 (file)
--- a/misc/cgo/testshared/shared_test.go
+++ b/misc/cgo/testshared/shared_test.go
@@ -203,6 +203,26 @@ func TestNoTextrel(t *testing.T) {
        }
 }
 
+// The shared library does not contain symbols called ".dup"
+func TestNoDupSymbols(t *testing.T) {
+       sopath := filepath.Join(gorootInstallDir, soname)
+       f, err := elf.Open(sopath)
+       if err != nil {
+               t.Fatal("elf.Open failed: ", err)
+       }
+       defer f.Close()
+       syms, err := f.Symbols()
+       if err != nil {
+               t.Errorf("error reading symbols %v", err)
+               return
+       }
+       for _, s := range syms {
+               if s.Name == ".dup" {
+                       t.Fatalf("%s contains symbol called .dup", sopath)
+               }
+       }
+}
+
 // The install command should have created a "shlibname" file for the
 // listed packages (and runtime/cgo, and math on arm) indicating the
 // name of the shared library containing it.

diff --git a/src/cmd/link/internal/ld/decodesym.go b/src/cmd/link/internal/ld/decodesym.go
index 00e1a79a83c2a436fe055938b708d9df734c3c1e..a7a62623d7024c5b7b146e6bd00d3d4a3a363d12 100644 (file)
--- a/src/cmd/link/internal/ld/decodesym.go
+++ b/src/cmd/link/internal/ld/decodesym.go
@@ -348,7 +348,7 @@ func decodetype_methods(s *LSym) []methodsig {
        numMethods := int(decode_inuxi(s.P[off+2*Thearch.Ptrsize:], Thearch.Intsize))
        r := decode_reloc(s, int32(off+Thearch.Ptrsize))
        if r.Sym != s {
-               panic(fmt.Sprintf("method slice pointer in %q leads to a different symbol", s.Name))
+               panic(fmt.Sprintf("method slice pointer in %s leads to a different symbol %s", s, r.Sym))
        }
        off = int(r.Add)                    // array of reflect.method values
        sizeofMethod := 5 * Thearch.Ptrsize // sizeof reflect.method in program

diff --git a/src/cmd/link/internal/ld/objfile.go b/src/cmd/link/internal/ld/objfile.go
index 04ac8d827fda412e0c720770f90ad4964a0b8c71..21b9d6e8209664fcf0b4ec4faba00346b414227f 100644 (file)
--- a/src/cmd/link/internal/ld/objfile.go
+++ b/src/cmd/link/internal/ld/objfile.go
@@ -175,8 +175,6 @@ func ldobjfile(ctxt *Link, f *obj.Biobuf, pkg string, length int64, pn string) {
        }
 }
 
-var readsym_ndup int
-
 func readsym(ctxt *Link, f *obj.Biobuf, pkg string, pn string) {
        if obj.Bgetc(f) != 0xfe {
                log.Fatalf("readsym out of sync")
@@ -211,8 +209,7 @@ func readsym(ctxt *Link, f *obj.Biobuf, pkg string, pn string) {
                }
                if len(s.P) > 0 {
                        dup = s
-                       s = linknewsym(ctxt, ".dup", readsym_ndup)
-                       readsym_ndup++ // scratch
+                       s = linknewsym(ctxt, ".dup", -1)
                }
        }
 

diff --git a/src/cmd/link/internal/ld/sym.go b/src/cmd/link/internal/ld/sym.go
index 05b3252add268eacc6119fe4ed02285a323224c1..e4fce6a5db6bc9b3dd064a2a91434a0730121ec8 100644 (file)
--- a/src/cmd/link/internal/ld/sym.go
+++ b/src/cmd/link/internal/ld/sym.go
@@ -173,7 +173,11 @@ func linknewsym(ctxt *Link, symb string, v int) *LSym {
        s.Version = int16(v)
        ctxt.Nsymbol++
 
-       ctxt.Allsym = append(ctxt.Allsym, s)
+       if v != -1 {
+               ctxt.Allsym = append(ctxt.Allsym, s)
+       } else if v < -1 {
+               ctxt.Diag("invalid version %d in linknewsym", v)
+       }
        return s
 }