misc/cgo/test: get uintptr, not pointer, from dlopen

The dlopen function returns an opaque handle, and it is possible for
it to look like a Go pointer, causing garbage collector and cgo
confusion.

Fixes #23663

Change-Id: Id080e2bbcee8cfa7ac4a457a927f96949eb913f8
Reviewed-on: https://go-review.googlesource.com/91596
Run-TryBot: Ian Lance Taylor <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Russ Cox <[email protected]>

Author: ianlancetaylor

misc/cgo/test/issue4029.c

@@ -4,6 +4,25 @@
 
 // +build !windows
 
+#include <stdint.h>
+#include <dlfcn.h>
+
+// Write our own versions of dlopen/dlsym/dlclose so that we represent
+// the opaque handle as a Go uintptr rather than a Go pointer to avoid
+// garbage collector confusion.  See issue 23663.
+
+uintptr_t dlopen4029(char* name, int flags) {
+	return (uintptr_t)(dlopen(name, flags));
+}
+
+uintptr_t dlsym4029(uintptr_t handle, char* name) {
+	return (uintptr_t)(dlsym((void*)(handle), name));
+}
+
+int dlclose4029(uintptr_t handle) {
+	return dlclose((void*)(handle));
+}
+
 void call4029(void *arg) {
 	void (*fn)(void) = arg;
 	fn();

misc/cgo/test/issue4029.go

@@ -7,10 +7,15 @@
 package cgotest
 
 /*
+#include <stdint.h>
 #include <dlfcn.h>
 #cgo linux LDFLAGS: -ldl
 
-extern void call4029(void *arg);
+extern uintptr_t dlopen4029(char*, int);
+extern uintptr_t dlsym4029(uintptr_t, char*);
+extern int dlclose4029(uintptr_t);
+
+extern void call4029(uintptr_t arg);
 */
 import "C"
 
@@ -51,15 +56,15 @@ func test4029(t *testing.T) {
 }
 
 func loadThySelf(t *testing.T, symbol string) {
-	this_process := C.dlopen(nil, C.RTLD_NOW)
-	if this_process == nil {
+	this_process := C.dlopen4029(nil, C.RTLD_NOW)
+	if this_process == 0 {
 		t.Error("dlopen:", C.GoString(C.dlerror()))
 		return
 	}
-	defer C.dlclose(this_process)
+	defer C.dlclose4029(this_process)
 
-	symbol_address := C.dlsym(this_process, C.CString(symbol))
-	if symbol_address == nil {
+	symbol_address := C.dlsym4029(this_process, C.CString(symbol))
+	if symbol_address == 0 {
 		t.Error("dlsym:", C.GoString(C.dlerror()))
 		return
 	}