[dev.link] cmd/internal/goobj2: change StringRef encoding for better locality
Previously, StringRef is encoded as an offset pointing to
{ len, [len]byte }. This CL changes it to { len, offset }, where
offset points the bytes.
With the new format, reading a string header is just reading two
adjacent uint32s, without accessing the string table. This should
improve locality of object file reading.
Change-Id: Iec30708f9d9adb2f0242db6c4767c0f8e730f4df
Reviewed-on: https://go-review.googlesource.com/c/go/+/226797
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
diff --git a/src/cmd/internal/goobj2/objfile.go b/src/cmd/internal/goobj2/objfile.go
index c0d47b4..db84e8a 100644
--- a/src/cmd/internal/goobj2/objfile.go
+++ b/src/cmd/internal/goobj2/objfile.go
@@ -26,17 +26,16 @@
// }
//
// Strings [...]struct {
-// Len uint32
// Data [...]byte
// }
//
-// Autolib [...]stringOff // imported packages (for file loading) // TODO: add fingerprints
-// PkgIndex [...]stringOff // referenced packages by index
+// Autolib [...]string // imported packages (for file loading) // TODO: add fingerprints
+// PkgIndex [...]string // referenced packages by index
//
-// DwarfFiles [...]stringOff
+// DwarfFiles [...]string
//
// SymbolDefs [...]struct {
-// Name stringOff
+// Name string
// ABI uint16
// Type uint8
// Flag uint8
@@ -69,8 +68,8 @@
// Data [...]byte
// Pcdata [...]byte
//
-// stringOff is a uint32 (?) offset that points to the corresponding
-// string, which is a uint32 length followed by that number of bytes.
+// string is encoded as is a uint32 length followed by a uint32 offset
+// that points to the corresponding string bytes.
//
// symRef is struct { PkgIdx, SymIdx uint32 }.
//
@@ -118,6 +117,8 @@
// Currently a symbol's Gotype and FuncInfo are auxiliary symbols. We
// may make use of aux symbols in more cases, e.g. DWARF symbols.
+const stringRefSize = 8 // two uint32s
+
// Package Index.
const (
PkgIdxNone = (1<<31 - 1) - iota // Non-package symbols
@@ -219,28 +220,28 @@
func (s *Sym) Read(r *Reader, off uint32) {
s.Name = r.StringRef(off)
- s.ABI = r.uint16At(off + 4)
- s.Type = r.uint8At(off + 6)
- s.Flag = r.uint8At(off + 7)
- s.Siz = r.uint32At(off + 8)
+ s.ABI = r.uint16At(off + 8)
+ s.Type = r.uint8At(off + 10)
+ s.Flag = r.uint8At(off + 11)
+ s.Siz = r.uint32At(off + 12)
}
// Read fields other than the symbol name. The name is not necessary
// in some cases, and most of the time spent in Read is reading the
// name.
func (s *Sym) ReadWithoutName(r *Reader, off uint32) {
- s.ABI = r.uint16At(off + 4)
- s.Type = r.uint8At(off + 6)
- s.Flag = r.uint8At(off + 7)
- s.Siz = r.uint32At(off + 8)
+ s.ABI = r.uint16At(off + 8)
+ s.Type = r.uint8At(off + 10)
+ s.Flag = r.uint8At(off + 11)
+ s.Siz = r.uint32At(off + 12)
}
func (s *Sym) ReadFlag(r *Reader, off uint32) {
- s.Flag = r.uint8At(off + 7)
+ s.Flag = r.uint8At(off + 11)
}
func (s *Sym) Size() int {
- return 4 + 2 + 1 + 1 + 4
+ return stringRefSize + 2 + 1 + 1 + 4
}
func (s *Sym) Dupok() bool { return s.Flag&SymFlagDupok != 0 }
@@ -400,7 +401,6 @@
return
}
w.stringMap[s] = w.off
- w.Uint32(uint32(len(s)))
w.RawString(s)
}
@@ -409,6 +409,7 @@
if !ok {
panic(fmt.Sprintf("writeStringRef: string not added: %q", s))
}
+ w.Uint32(uint32(len(s)))
w.Uint32(off)
}
@@ -506,9 +507,8 @@
return b[0]
}
-func (r *Reader) StringAt(off uint32) string {
- l := r.uint32At(off)
- b := r.b[off+4 : off+4+l]
+func (r *Reader) StringAt(off uint32, len uint32) string {
+ b := r.b[off : off+len]
if r.readonly {
return toString(b) // backed by RO memory, ok to make unsafe string
}
@@ -530,44 +530,45 @@
}
func (r *Reader) StringRef(off uint32) string {
- return r.StringAt(r.uint32At(off))
+ l := r.uint32At(off)
+ return r.StringAt(r.uint32At(off+4), l)
}
func (r *Reader) Autolib() []string {
- n := (r.h.Offsets[BlkAutolib+1] - r.h.Offsets[BlkAutolib]) / 4
+ n := (r.h.Offsets[BlkAutolib+1] - r.h.Offsets[BlkAutolib]) / stringRefSize
s := make([]string, n)
for i := range s {
- off := r.h.Offsets[BlkAutolib] + uint32(i)*4
+ off := r.h.Offsets[BlkAutolib] + uint32(i)*stringRefSize
s[i] = r.StringRef(off)
}
return s
}
func (r *Reader) Pkglist() []string {
- n := (r.h.Offsets[BlkPkgIdx+1] - r.h.Offsets[BlkPkgIdx]) / 4
+ n := (r.h.Offsets[BlkPkgIdx+1] - r.h.Offsets[BlkPkgIdx]) / stringRefSize
s := make([]string, n)
for i := range s {
- off := r.h.Offsets[BlkPkgIdx] + uint32(i)*4
+ off := r.h.Offsets[BlkPkgIdx] + uint32(i)*stringRefSize
s[i] = r.StringRef(off)
}
return s
}
func (r *Reader) NPkg() int {
- return int(r.h.Offsets[BlkPkgIdx+1]-r.h.Offsets[BlkPkgIdx]) / 4
+ return int(r.h.Offsets[BlkPkgIdx+1]-r.h.Offsets[BlkPkgIdx]) / stringRefSize
}
func (r *Reader) Pkg(i int) string {
- off := r.h.Offsets[BlkPkgIdx] + uint32(i)*4
+ off := r.h.Offsets[BlkPkgIdx] + uint32(i)*stringRefSize
return r.StringRef(off)
}
func (r *Reader) NDwarfFile() int {
- return int(r.h.Offsets[BlkDwarfFile+1]-r.h.Offsets[BlkDwarfFile]) / 4
+ return int(r.h.Offsets[BlkDwarfFile+1]-r.h.Offsets[BlkDwarfFile]) / stringRefSize
}
func (r *Reader) DwarfFile(i int) string {
- off := r.h.Offsets[BlkDwarfFile] + uint32(i)*4
+ off := r.h.Offsets[BlkDwarfFile] + uint32(i)*stringRefSize
return r.StringRef(off)
}
