[release-branch.go1.19 cmd/compile: align stack offset to alignment larger than PtrSize

In typebits.Set we check that the offset is a multiple of the
alignment, which makes perfect sense. But for values like
atomic.Int64, which has 8-byte alignment even on 32-bit platforms
(i.e. the alignment is larger than PtrSize), if it is on stack it
may be under-aligned, as the stack frame is only PtrSize aligned.

Normally we would prevent such values on stack, as the escape
analysis force values with higher alignment to heap. But for a
composite literal assignment like x = AlignedType{...}, the
compiler creates an autotmp for the RHS then copies it to the LHS.
The autotmp is on stack and may be under-aligned. Currently this
may cause an ICE in the typebits.Set check.

This CL makes it align the _offset_ of the autotmp to 8 bytes,
which satisfies the check. Note that this is actually lying: the
actual address at run time may not necessarily be 8-byte
aligned as we only align SP to 4 bytes.

The under-alignment is probably okay. The only purpose for the
autotmp is to copy the value to the LHS, and the copying code we
generate (at least currently) doesn't care the alignment beyond
stack alignment.

Updates #54638.
Fixes #54697.

Change-Id: I13c16afde2eea017479ff11dfc24092bcb8aba6a
Reviewed-on: https://go-review.googlesource.com/c/go/+/425256
Run-TryBot: Cherry Mui <cherryyz@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
(cherry picked from commit 1211a62bdcb0f070c5082255bcc90e1a14c16bb2)
Reviewed-on: https://go-review.googlesource.com/c/go/+/425935

diff --git a/src/cmd/compile/internal/ssagen/pgen.go b/src/cmd/compile/internal/ssagen/pgen.go
index 825b32aa8082497ba7527397585fb9c32719d416..711bdef9061340b4ac9dbc601c9a236a0ff60e05 100644 (file)
--- a/src/cmd/compile/internal/ssagen/pgen.go
+++ b/src/cmd/compile/internal/ssagen/pgen.go
@@ -96,6 +96,7 @@ func needAlloc(n *ir.Name) bool {
 func (s *ssafn) AllocFrame(f *ssa.Func) {
        s.stksize = 0
        s.stkptrsize = 0
+       s.stkalign = int64(types.RegSize)
        fn := s.curfn
 
        // Mark the PAUTO's unused.
@@ -160,6 +161,9 @@ func (s *ssafn) AllocFrame(f *ssa.Func) {
                }
                s.stksize += w
                s.stksize = types.Rnd(s.stksize, n.Type().Alignment())
+               if n.Type().Alignment() > int64(types.RegSize) {
+                       s.stkalign = n.Type().Alignment()
+               }
                if n.Type().HasPointers() {
                        s.stkptrsize = s.stksize
                        lastHasPtr = true
@@ -169,8 +173,8 @@ func (s *ssafn) AllocFrame(f *ssa.Func) {
                n.SetFrameOffset(-s.stksize)
        }
 
-       s.stksize = types.Rnd(s.stksize, int64(types.RegSize))
-       s.stkptrsize = types.Rnd(s.stkptrsize, int64(types.RegSize))
+       s.stksize = types.Rnd(s.stksize, s.stkalign)
+       s.stkptrsize = types.Rnd(s.stkptrsize, s.stkalign)
 }
 
 const maxStackSize = 1 << 30

diff --git a/src/cmd/compile/internal/ssagen/ssa.go b/src/cmd/compile/internal/ssagen/ssa.go
index 83def791f758d23bc58a63133e5b952e34195daf..809395875cd0f2554a51469e897afb0f8b977e57 100644 (file)
--- a/src/cmd/compile/internal/ssagen/ssa.go
+++ b/src/cmd/compile/internal/ssagen/ssa.go
@@ -7337,7 +7337,8 @@ func genssa(f *ssa.Func, pp *objw.Progs) {
 func defframe(s *State, e *ssafn, f *ssa.Func) {
        pp := s.pp
 
-       frame := types.Rnd(s.maxarg+e.stksize, int64(types.RegSize))
+       s.maxarg = types.Rnd(s.maxarg, e.stkalign)
+       frame := s.maxarg + e.stksize
        if Arch.PadFrame != nil {
                frame = Arch.PadFrame(frame)
        }
@@ -7775,7 +7776,14 @@ type ssafn struct {
        strings    map[string]*obj.LSym // map from constant string to data symbols
        stksize    int64                // stack size for current frame
        stkptrsize int64                // prefix of stack containing pointers
-       log        bool                 // print ssa debug to the stdout
+
+       // alignment for current frame.
+       // NOTE: when stkalign > PtrSize, currently this only ensures the offsets of
+       // objects in the stack frame are aligned. The stack pointer is still aligned
+       // only PtrSize.
+       stkalign int64
+
+       log bool // print ssa debug to the stdout
 }
 
 // StringData returns a symbol which

diff --git a/test/fixedbugs/issue54638.go b/test/fixedbugs/issue54638.go
new file mode 100644 (file)
index 0000000..d0258b0
--- /dev/null
+++ b/test/fixedbugs/issue54638.go
@@ -0,0 +1,40 @@
+// compile
+
+// Copyright 2022 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.
+
+// Issue 54638: composite literal assignment with
+// alignment > PtrSize causes ICE.
+
+package p
+
+import "sync/atomic"
+
+type S struct{ l any }
+
+type T struct {
+       H any
+       a [14]int64
+       f func()
+       x atomic.Int64
+}
+
+//go:noinline
+func (T) M(any) {}
+
+type W [2]int64
+
+//go:noinline
+func (W) Done() {}
+
+func F(l any) [3]*int {
+       var w W
+       var x [3]*int // use some stack
+       t := T{H: S{l: l}}
+       go func() {
+               t.M(l)
+               w.Done()
+       }()
+       return x
+}