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cmd/compile: be stricter about recognizing safety rule #4

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unsafe.Pointer safety rule #4 says "The compiler handles a Pointer
converted to a uintptr in the argument list of a call". Within escape
analysis, we've always required this be a single conversion
unsafe.Pointer->uintptr conversion, but the corresponding logic in
order is somewhat laxer, allowing arbitrary chains of OCONVNOPs from
unsafe.Pointer to uintptr.

This CL changes order to be stricter to match escape analysis.

Passes toolstash-check.

Change-Id: Iadd210d2123accb2020f5728ea2a47814f703352
Reviewed-on: https://go-review.googlesource.com/c/go/+/229578
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Matthew Dempsky 2020-04-22 14:37:02 -07:00
parent ed7888aea6
commit f049d911e9
2 changed files with 24 additions and 19 deletions
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12
doc/go1.15.html
View File

@ -84,6 +84,18 @@ TODO
TODO
</p>
<h2 id="compiler">Compiler</h2>
<p><!-- https://golang.org/cl/229578 -->
Package <code>unsafe</code>'s <a href="/pkg/unsafe/#Pointer">safety
rules</a> allow converting an <code>unsafe.Pointer</code>
into <code>uintptr</code> when calling certain
functions. Previously, in some cases, the compiler allowed multiple
chained conversions (for example, <code>syscall.Syscall(…,
uintptr(uintptr(ptr)), …)</code>). The compiler now requires exactly
one conversion. Code that used multiple conversions should be
updated to satisfy the safety rules.
</p>
<h2 id="library">Core library</h2>

27
src/cmd/compile/internal/gc/order.go
View File

@ -414,34 +414,27 @@ func (o *Order) call(n *Node) {
if n.Op != OCALLFUNC && n.Op != OCALLMETH {
return
}
keepAlive := func(i int) {
keepAlive := func(arg *Node) {
// If the argument is really a pointer being converted to uintptr,
// arrange for the pointer to be kept alive until the call returns,
// by copying it into a temp and marking that temp
// still alive when we pop the temp stack.
xp := n.List.Addr(i)
for (*xp).Op == OCONVNOP && !(*xp).Type.IsUnsafePtr() {
xp = &(*xp).Left
}
x := *xp
if x.Type.IsUnsafePtr() {
x = o.copyExpr(x, x.Type, false)
if arg.Op == OCONVNOP && arg.Left.Type.IsUnsafePtr() {
x := o.copyExpr(arg.Left, arg.Left.Type, false)
x.Name.SetKeepalive(true)
*xp = x
arg.Left = x
}
}
for i, t := range n.Left.Type.Params().FieldSlice() {
// Check for "unsafe-uintptr" tag provided by escape analysis.
if t.IsDDD() && !n.IsDDD() {
if t.Note == uintptrEscapesTag {
for ; i < n.List.Len(); i++ {
keepAlive(i)
}
for i, param := range n.Left.Type.Params().FieldSlice() {
if param.Note == unsafeUintptrTag || param.Note == uintptrEscapesTag {
if param.IsDDD() && !n.IsDDD() {
for _, arg := range n.List.Slice()[i:] {
keepAlive(arg)
}
} else {
if t.Note == unsafeUintptrTag || t.Note == uintptrEscapesTag {
keepAlive(i)
keepAlive(n.List.Index(i))
}
}
}