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[dev.link] cmd/link: add support for "not in symbol table" attribute

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Add loader.Loader support for recording whether symbols should appear
in the symbol table (e.g. AttrNotInSymbolTable). Change the preloader
to apply this attribute to selected symbols (e.g. go.string.*,
runtime.gcbits.*) during the initial scan over object file defs, since
at that point the name is available.

Change-Id: I54be9a649107e90c0fd544a1c0ba87e2d98833ad
Reviewed-on: https://go-review.googlesource.com/c/go/+/213778
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
This commit is contained in:
Than McIntosh 2020-01-07 15:47:43 -05:00
parent 3fa9500dd1
commit e5dc6ff874
1 changed files with 30 additions and 2 deletions
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32
src/cmd/link/internal/loader/loader.go
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@ -178,6 +178,7 @@ type Loader struct {
attrReachable bitmap // reachable symbols, indexed by global index
attrOnList bitmap // "on list" symbols, indexed by global index
attrLocal bitmap // "local" symbols, indexed by global index
attrNotInSymbolTable bitmap // "not in symtab" symbols, indexed by glob idx
attrVisibilityHidden bitmap // hidden symbols, indexed by ext sym index
attrDuplicateOK bitmap // dupOK symbols, indexed by ext sym index
attrShared bitmap // shared symbols, indexed by ext sym index
@ -797,6 +798,22 @@ func (l *Loader) SetAttrLocal(i Sym, v bool) {
}
}
// AttrNotInSymbolTable returns true for symbols that should not be
// added to the symbol table of the final generated load module.
func (l *Loader) AttrNotInSymbolTable(i Sym) bool {
return l.attrNotInSymbolTable.has(i)
}
// SetAttrNotInSymbolTable the "not in symtab" property for a symbol
// (see AttrNotInSymbolTable above).
func (l *Loader) SetAttrNotInSymbolTable(i Sym, v bool) {
if v {
l.attrNotInSymbolTable.set(i)
} else {
l.attrNotInSymbolTable.unset(i)
}
}
// AttrVisibilityHidden symbols returns true for ELF symbols with
// visibility set to STV_HIDDEN. They become local symbols in
// the final executable. Only relevant when internally linking
@ -1393,6 +1410,7 @@ func (l *Loader) growAttrBitmaps(reqLen int) {
l.attrReachable = growBitmap(reqLen, l.attrReachable)
l.attrOnList = growBitmap(reqLen, l.attrOnList)
l.attrLocal = growBitmap(reqLen, l.attrLocal)
l.attrNotInSymbolTable = growBitmap(reqLen, l.attrNotInSymbolTable)
}
// These are indexed by external symbol offset (e.g. i - l.extStart)
if l.extStart == 0 {
@ -1552,6 +1570,7 @@ func (l *Loader) Preload(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, lib *
ndef := r.NSym()
nnonpkgdef := r.NNonpkgdef()
l.growAttrBitmaps(int(istart) + ndef + nnonpkgdef)
for i, n := 0, ndef+nnonpkgdef; i < n; i++ {
osym := goobj2.Sym{}
osym.Read(r, r.SymOff(i))
@ -1562,15 +1581,22 @@ func (l *Loader) Preload(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, lib *
v := abiToVer(osym.ABI, localSymVersion)
dupok := osym.Dupok()
added := l.AddSym(name, v, istart+Sym(i), or, dupok, sym.AbiSymKindToSymKind[objabi.SymKind(osym.Type)])
if added && strings.HasPrefix(name, "go.itablink.") {
if !added {
continue
}
if strings.HasPrefix(name, "go.itablink.") {
l.itablink[istart+Sym(i)] = struct{}{}
}
if added && strings.HasPrefix(name, "runtime.") {
if strings.HasPrefix(name, "runtime.") {
if bi := goobj2.BuiltinIdx(name, v); bi != -1 {
// This is a definition of a builtin symbol. Record where it is.
l.builtinSyms[bi] = istart + Sym(i)
}
}
if strings.HasPrefix(name, "go.string.") ||
strings.HasPrefix(name, "runtime.gcbits.") {
l.SetAttrNotInSymbolTable(istart+Sym(i), true)
}
}
// The caller expects us consuming all the data
@ -2030,6 +2056,7 @@ func (l *Loader) copyAttributes(src Sym, dst Sym) {
l.SetAttrReachable(dst, l.AttrReachable(src))
l.SetAttrOnList(dst, l.AttrOnList(src))
l.SetAttrLocal(dst, l.AttrLocal(src))
l.SetAttrNotInSymbolTable(dst, l.AttrNotInSymbolTable(src))
l.SetAttrVisibilityHidden(dst, l.AttrVisibilityHidden(src))
l.SetAttrDuplicateOK(dst, l.AttrDuplicateOK(src))
l.SetAttrShared(dst, l.AttrShared(src))
@ -2047,6 +2074,7 @@ func (l *Loader) migrateAttributes(src Sym, dst *sym.Symbol) {
dst.Attr.Set(sym.AttrReachable, l.AttrReachable(src))
dst.Attr.Set(sym.AttrOnList, l.AttrOnList(src))
dst.Attr.Set(sym.AttrLocal, l.AttrLocal(src))
dst.Attr.Set(sym.AttrNotInSymbolTable, l.AttrNotInSymbolTable(src))
dst.Attr.Set(sym.AttrVisibilityHidden, l.AttrVisibilityHidden(src))
dst.Attr.Set(sym.AttrDuplicateOK, l.AttrDuplicateOK(src))
dst.Attr.Set(sym.AttrShared, l.AttrShared(src))