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[dev.link] cmd/internal/goobj2: change StringRef encoding for better locality

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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>
This commit is contained in:
Cherry Zhang 2020-03-31 20:01:46 -04:00
parent 4ec5e7c50f
commit ff29f97437
1 changed files with 31 additions and 30 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

61
src/cmd/internal/goobj2/objfile.go
View file

@ -26,17 +26,16 @@ import (
// }
//
// 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 @@ import (
// 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 @@ import (
// 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) Write(w *Writer) {
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 @@ func (w *Writer) AddString(s string) {
return
}
w.stringMap[s] = w.off
w.Uint32(uint32(len(s)))
w.RawString(s)
}
@ -409,6 +409,7 @@ func (w *Writer) StringRef(s string) {
if !ok {
panic(fmt.Sprintf("writeStringRef: string not added: %q", s))
}
w.Uint32(uint32(len(s)))
w.Uint32(off)
}
@ -506,9 +507,8 @@ func (r *Reader) uint8At(off uint32) uint8 {
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 toString(b []byte) string {
}
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)
}