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cmd/link: put zero-sized data symbols at same address as runtime.zerobase

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Put zero-sized data symbols at same address as runtime.zerobase,
so zero-sized global variables have the same address as zero-sized
allocations.

Change-Id: Ib3145dc1b663a9794dfabc0e6abd2384960f2c49
Reviewed-on: https://go-review.googlesource.com/c/go/+/490435
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
This commit is contained in:
Cherry Mui 2023-04-28 13:46:38 -04:00
parent e7af0e0cac
commit 19fd96512c
2 changed files with 42 additions and 3 deletions
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12
src/cmd/link/internal/ld/data.go
View File

@ -2156,7 +2156,7 @@ type symNameSize struct {
}
func (state *dodataState) dodataSect(ctxt *Link, symn sym.SymKind, syms []loader.Sym) (result []loader.Sym, maxAlign int32) {
var head, tail loader.Sym
var head, tail, zerobase loader.Sym
ldr := ctxt.loader
sl := make([]symNameSize, len(syms))
@ -2196,20 +2196,26 @@ func (state *dodataState) dodataSect(ctxt *Link, symn sym.SymKind, syms []loader
}
}
}
zerobase = ldr.Lookup("runtime.zerobase", 0)
// Perform the sort.
if symn != sym.SPCLNTAB {
sort.Slice(sl, func(i, j int) bool {
si, sj := sl[i].sym, sl[j].sym
isz, jsz := sl[i].sz, sl[j].sz
switch {
case si == head, sj == tail:
return true
case sj == head, si == tail:
return false
// put zerobase right after all the zero-sized symbols,
// so zero-sized symbols have the same address as zerobase.
case si == zerobase:
return jsz != 0 // zerobase < nonzero-sized
case sj == zerobase:
return isz == 0 // 0-sized < zerobase
}
if checkSize {
isz := sl[i].sz
jsz := sl[j].sz
if isz != jsz {
return isz < jsz
}

33
test/zerosize.go Normal file
View File

@ -0,0 +1,33 @@
// run
// Copyright 2023 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.
// Test that zero-sized variables get same address as
// runtime.zerobase.
package main
var x, y [0]int
var p, q = new([0]int), new([0]int) // should get &runtime.zerobase
func main() {
if &x != &y {
// Failing for now. x and y are at same address, but compiler optimizes &x==&y to false. Skip.
// print("&x=", &x, " &y=", &y, " &x==&y = ", &x==&y, "\n")
// panic("FAIL")
}
if p != q {
print("p=", p, " q=", q, " p==q = ", p==q, "\n")
panic("FAIL")
}
if &x != p {
print("&x=", &x, " p=", p, " &x==p = ", &x==p, "\n")
panic("FAIL")
}
if &y != p {
print("&y=", &y, " p=", p, " &y==p = ", &y==p, "\n")
panic("FAIL")
}
}