qbit/go
1
0
Fork 0
mirror of https://github.com/golang/go synced 2024-11-06 15:46:19 -07:00
Code Releases Activity

[dev.link] cmd/compile, cmd/asm: add length to hashed symbols

Browse Source 
While working on deduplicating pcdata, I found that the following hashed
symbols would result in the same:

[] == [0,0,0,0....]

This makes using content addressable symbols untenable for pcdata.
Adding the length to the hash keeps the dream alive.

No difference in binary size (darwin, cmd/compile), spurious
improvements in DWARF phase memory.

Change-Id: I21101f7754a3d870922b0dea39c947cc8509432f
Reviewed-on: https://go-review.googlesource.com/c/go/+/247903
Run-TryBot: Jeremy Faller <jeremy@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
This commit is contained in:
Jeremy Faller 2020-08-12 12:54:03 -04:00
parent 9ae8f71c94
commit b249703e3c
1 changed files with 13 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
src/cmd/internal/obj/objfile.go
View File

@ -372,10 +372,22 @@ func contentHash64(s *LSym) goobj.Hash64Type {
// hashed symbols.
func (w *writer) contentHash(s *LSym) goobj.HashType {
h := sha1.New()
var tmp [14]byte
// Include the size of the symbol in the hash.
// This preserves the length of symbols, preventing the following two symbols
// from hashing the same:
//
// [2]int{1,2} ≠ [10]int{1,2,0,0,0...}
//
// In this case, if the smaller symbol is alive, the larger is not kept unless
// needed.
binary.LittleEndian.PutUint64(tmp[:8], uint64(s.Size))
h.Write(tmp[:8])
// The compiler trims trailing zeros _sometimes_. We just do
// it always.
h.Write(bytes.TrimRight(s.P, "\x00"))
var tmp [14]byte
for i := range s.R {
r := &s.R[i]
binary.LittleEndian.PutUint32(tmp[:4], uint32(r.Off))