Stowage/go
2
0
Fork 0
mirror of https://github.com/golang/go.git synced 2025-12-08 06:10:04 +00:00
Code Issues Projects Releases Packages Wiki Activity

cgo: adjust return value location to account for stack copies.

Browse source 
During a cgo call, the stack can be copied.  This copy invalidates
the pointer that cgo has into the return value area.  To fix this
problem, pass the address of the location containing the stack
top value (which is in the G struct).  For cgo functions which
return values, read the stktop before and after the cgo call to
compute the adjustment necessary to write the return value.

Fixes #8771

LGTM=iant, rsc
R=iant, rsc, khr
CC=golang-codereviews
https://golang.org/cl/144130043
This commit is contained in:
Keith Randall 2014-09-25 07:59:01 -07:00
parent dfaf1f71e6
commit 1b6807bb06
9 changed files with 161 additions and 50 deletions
Download patch file Download diff file Expand all files Collapse all files

16
src/cmd/cgo/out.go
View file

@ -44,6 +44,7 @@ func (p *Package) writeDefs() {
fmt.Fprintf(fm, "int main() { return 0; }\n")
if *importRuntimeCgo {
fmt.Fprintf(fm, "void crosscall2(void(*fn)(void*, int), void *a, int c) { }\n")
fmt.Fprintf(fm, "char* cgo_topofstack(void) { return (char*)0; }\n")
} else {
// If we're not importing runtime/cgo, we *are* runtime/cgo,
// which provides crosscall2. We just need a prototype.
@ -519,9 +520,13 @@ func (p *Package) writeOutputFunc(fgcc *os.File, n *Name) {
// Use packed attribute to force no padding in this struct in case
// gcc has different packing requirements.
fmt.Fprintf(fgcc, "\t%s %v *a = v;\n", ctype, p.packedAttribute())
if n.FuncType.Result != nil {
// Save the stack top for use below.
fmt.Fprintf(fgcc, "\tchar *stktop = cgo_topofstack();\n")
}
fmt.Fprintf(fgcc, "\t")
if t := n.FuncType.Result; t != nil {
fmt.Fprintf(fgcc, "a->r = ")
fmt.Fprintf(fgcc, "__typeof__(a->r) r = ")
if c := t.C.String(); c[len(c)-1] == '*' {
fmt.Fprint(fgcc, "(__typeof__(a->r)) ")
}
@ -544,6 +549,13 @@ func (p *Package) writeOutputFunc(fgcc *os.File, n *Name) {
fmt.Fprintf(fgcc, "a->p%d", i)
}
fmt.Fprintf(fgcc, ");\n")
if n.FuncType.Result != nil {
// The cgo call may have caused a stack copy (via a callback).
// Adjust the return value pointer appropriately.
fmt.Fprintf(fgcc, "\ta = (void*)((char*)a + (cgo_topofstack() - stktop));\n")
// Save the return value.
fmt.Fprintf(fgcc, "\ta->r = r;\n")
}
if n.AddError {
fmt.Fprintf(fgcc, "\treturn errno;\n")
}
@ -1131,6 +1143,8 @@ __cgo_size_assert(__cgo_long_long, 8)
__cgo_size_assert(float, 4)
__cgo_size_assert(double, 8)
extern char* cgo_topofstack(void);
#include <errno.h>
#include <string.h>
`