cgo: use correct frame size for 0 arguments

Passing a frame size of 1 was causing the cgo callback
to push 1 byte of arguments onto the stack, making
the stack pointer misaligned, which had the effect of
hiding all the pointers on the stack from the garbage
collector.

SWIG only wraps calls to C++ virtual methods, so it
always has at least 1 argument, so SWIG does not need
to be fixed too.

Fixes #1328.

R=iant
CC=golang-dev
https://golang.org/cl/4261046

diff --git a/src/cmd/cgo/out.go b/src/cmd/cgo/out.go
index 279a9c15c7655dba5313e5a62a0a04d33621441f..4d903dbeeb8ea20921b87a861eeb98b5a31bb76e 100644 (file)
--- a/src/cmd/cgo/out.go
+++ b/src/cmd/cgo/out.go
@@ -180,7 +180,6 @@ func (p *Package) structType(n *Name) (string, int64) {
        }
        if off == 0 {
                fmt.Fprintf(&buf, "\t\tchar unused;\n") // avoid empty struct
-               off++
        }
        fmt.Fprintf(&buf, "\t}")
        return buf.String(), off
@@ -225,6 +224,9 @@ func (p *Package) writeDefsFunc(fc, fgo2 *os.File, n *Name) {
        fmt.Fprintf(fc, "void _cgo%s%s(void*);\n", cPrefix, n.Mangle)
        fmt.Fprintf(fc, "\n")
        fmt.Fprintf(fc, "void\n")
+       if argSize == 0 {
+               argSize++
+       }
        fmt.Fprintf(fc, "·%s(struct{uint8 x[%d];}p)\n", n.Mangle, argSize)
        fmt.Fprintf(fc, "{\n")
        fmt.Fprintf(fc, "\truntime·cgocall(_cgo%s%s, &p);\n", cPrefix, n.Mangle)
@@ -392,7 +394,6 @@ func (p *Package) writeExports(fgo2, fc, fm *os.File) {
                }
                if ctype == "struct {\n" {
                        ctype += "\t\tchar unused;\n" // avoid empty struct
-                       off++
                }
                ctype += "\t}"
 
@@ -444,7 +445,7 @@ func (p *Package) writeExports(fgo2, fc, fm *os.File) {
                        func(i int, atype ast.Expr) {
                                fmt.Fprintf(fgcc, "\ta.p%d = p%d;\n", i, i)
                        })
-               fmt.Fprintf(fgcc, "\tcrosscall2(_cgoexp%s_%s, &a, (int) sizeof a);\n", cPrefix, exp.ExpName)
+               fmt.Fprintf(fgcc, "\tcrosscall2(_cgoexp%s_%s, &a, %d);\n", cPrefix, exp.ExpName, off)
                if gccResult != "void" {
                        if len(fntype.Results.List) == 1 && len(fntype.Results.List[0].Names) <= 1 {
                                fmt.Fprintf(fgcc, "\treturn a.r0;\n")