cmd/compile: fix bug in DWARF inl handling of unused autos

The DWARF inline info generation hooks weren't properly
handling unused auto vars in certain cases, triggering an assert (now
fixed). Also with this change, introduce a new autom "flavor" to
use for autom entries that are added to insure that a specific
auto type makes it into the linker (this is a follow-on to the fix
for 22941).

Fixes #22962.

Change-Id: I7a2d8caf47f6ca897b12acb6a6de0eb25f5cac8f
Reviewed-on: https://go-review.googlesource.com/81557
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

diff --git a/src/cmd/compile/internal/gc/pgen.go b/src/cmd/compile/internal/gc/pgen.go
index 3d099ad6c052bf4a3d43f967a44ada6b95e725c9..cf99931bb5f28e2250055f23e1ca1f7ed534f038 100644 (file)
--- a/src/cmd/compile/internal/gc/pgen.go
+++ b/src/cmd/compile/internal/gc/pgen.go
@@ -322,7 +322,11 @@ func debuginfo(fnsym *obj.LSym, curfn interface{}) ([]dwarf.Scope, dwarf.InlCall
                switch n.Class() {
                case PAUTO:
                        if !n.Name.Used() {
-                               Fatalf("debuginfo unused node (AllocFrame should truncate fn.Func.Dcl)")
+                               // Text == nil -> generating abstract function
+                               if fnsym.Func.Text != nil {
+                                       Fatalf("debuginfo unused node (AllocFrame should truncate fn.Func.Dcl)")
+                               }
+                               continue
                        }
                        name = obj.NAME_AUTO
                case PPARAM, PPARAMOUT:
@@ -558,15 +562,14 @@ func createDwarfVars(fnsym *obj.LSym, debugInfo *ssa.FuncDebug, automDecls []*No
                        InlIndex:      int32(inlIndex),
                        ChildIndex:    -1,
                })
-               // Note: the auto that we're appending here is simply to insure
-               // that the DWARF type in question is picked up by the linker --
-               // there isn't a real auto variable with this name. This is
-               // to fix issue 22941.
+               // Append a "deleted auto" entry to the autom list so as to
+               // insure that the type in question is picked up by the linker.
+               // See issue 22941.
                gotype := ngotype(n).Linksym()
                fnsym.Func.Autom = append(fnsym.Func.Autom, &obj.Auto{
                        Asym:    Ctxt.Lookup(n.Sym.Name),
                        Aoffset: int32(-1),
-                       Name:    obj.NAME_AUTO,
+                       Name:    obj.NAME_DELETED_AUTO,
                        Gotype:  gotype,
                })
 

diff --git a/src/cmd/internal/obj/link.go b/src/cmd/internal/obj/link.go
index 090b1c604bbe0a70cc83e42ec703ed9be6010f86..27c74f6a77660d1c20a3863c687b7714d94aedd6 100644 (file)
--- a/src/cmd/internal/obj/link.go
+++ b/src/cmd/internal/obj/link.go
@@ -208,6 +208,9 @@ const (
        // A reference to name@GOT(SB) is a reference to the entry in the global offset
        // table for 'name'.
        NAME_GOTREF
+       // Indicates auto that was optimized away, but whose type
+       // we want to preserve in the DWARF debug info.
+       NAME_DELETED_AUTO
 )
 
 type AddrType uint8

diff --git a/src/cmd/internal/obj/objfile.go b/src/cmd/internal/obj/objfile.go
index 1a21bcdeb3b39432a3ec493f678c7fd2d1a5f5b6..2501bba663803bd771e17f6d91dfca181a6d7c89 100644 (file)
--- a/src/cmd/internal/obj/objfile.go
+++ b/src/cmd/internal/obj/objfile.go
@@ -351,6 +351,8 @@ func (w *objWriter) writeSym(s *LSym) {
                        w.writeInt(objabi.A_AUTO)
                } else if a.Name == NAME_PARAM {
                        w.writeInt(objabi.A_PARAM)
+               } else if a.Name == NAME_DELETED_AUTO {
+                       w.writeInt(objabi.A_DELETED_AUTO)
                } else {
                        log.Fatalf("%s: invalid local variable type %d", s.Name, a.Name)
                }

diff --git a/src/cmd/internal/objabi/autotype.go b/src/cmd/internal/objabi/autotype.go
index 17c42931310ffb442d7b5ab3520122de6e7cb499..1b46b0ffece3bc79ce706cd7d2390b55a526623a 100644 (file)
--- a/src/cmd/internal/objabi/autotype.go
+++ b/src/cmd/internal/objabi/autotype.go
@@ -34,4 +34,5 @@ package objabi
 const (
        A_AUTO = 1 + iota
        A_PARAM
+       A_DELETED_AUTO
 )

diff --git a/src/cmd/link/internal/ld/dwarf.go b/src/cmd/link/internal/ld/dwarf.go
index b2cd1f1b6a297f08bf474fe70dcfd2edc7d831e6..4642bdbe7a802a8846f2dadb6ea994b96afd9f6c 100644 (file)
--- a/src/cmd/link/internal/ld/dwarf.go
+++ b/src/cmd/link/internal/ld/dwarf.go
@@ -857,7 +857,7 @@ func defdwsymb(ctxt *Link, s *sym.Symbol, str string, t SymbolType, v int64, got
                }
                fallthrough
 
-       case AutoSym, ParamSym:
+       case AutoSym, ParamSym, DeletedAutoSym:
                dt = defgotype(ctxt, gotype)
        }
 

diff --git a/src/cmd/link/internal/ld/lib.go b/src/cmd/link/internal/ld/lib.go
index cd8b45cd2ee94e23597f897020af7d6ba741cc1f..6dcaf64122f918c85d9e3bcb46d59e60dae38672 100644 (file)
--- a/src/cmd/link/internal/ld/lib.go
+++ b/src/cmd/link/internal/ld/lib.go
@@ -1964,6 +1964,7 @@ func doversion() {
 type SymbolType int8
 
 const (
+       // see also http://9p.io/magic/man2html/1/nm
        TextSym      SymbolType = 'T'
        DataSym                 = 'D'
        BSSSym                  = 'B'
@@ -1972,6 +1973,9 @@ const (
        FrameSym                = 'm'
        ParamSym                = 'p'
        AutoSym                 = 'a'
+
+       // Deleted auto (not a real sym, just placeholder for type)
+       DeletedAutoSym = 'x'
 )
 
 func genasmsym(ctxt *Link, put func(*Link, *sym.Symbol, string, SymbolType, int64, *sym.Symbol)) {
@@ -2096,6 +2100,11 @@ func genasmsym(ctxt *Link, put func(*Link, *sym.Symbol, string, SymbolType, int6
                        continue
                }
                for _, a := range s.FuncInfo.Autom {
+                       if a.Name == objabi.A_DELETED_AUTO {
+                               put(ctxt, nil, "", DeletedAutoSym, 0, a.Gotype)
+                               continue
+                       }
+
                        // Emit a or p according to actual offset, even if label is wrong.
                        // This avoids negative offsets, which cannot be encoded.
                        if a.Name != objabi.A_AUTO && a.Name != objabi.A_PARAM {

diff --git a/test/fixedbugs/issue22962.dir/a.go b/test/fixedbugs/issue22962.dir/a.go
new file mode 100644 (file)
index 0000000..7257d7d
--- /dev/null
+++ b/test/fixedbugs/issue22962.dir/a.go
@@ -0,0 +1,11 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package a
+
+func F() {
+       if x := 0; false {
+               _ = x
+       }
+}

diff --git a/test/fixedbugs/issue22962.dir/b.go b/test/fixedbugs/issue22962.dir/b.go
new file mode 100644 (file)
index 0000000..e1568c8
--- /dev/null
+++ b/test/fixedbugs/issue22962.dir/b.go
@@ -0,0 +1,9 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package b
+
+import "a"
+
+var V = func() { a.F() }

diff --git a/test/fixedbugs/issue22962.go b/test/fixedbugs/issue22962.go
new file mode 100644 (file)
index 0000000..8000a52
--- /dev/null
+++ b/test/fixedbugs/issue22962.go
@@ -0,0 +1,7 @@
+// compiledir
+
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ignored