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// Copyright 2015 Luke Shumaker <lukeshu@sbcglobal.net>.
//
// This is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; either version 2 of
// the License, or (at your option) any later version.
//
// The GNU General Public License's references to "object code" and
// "executables" are to be interpreted to also include the output of
// any document formatting or typesetting system, including
// intermediate and printed output.
//
// This software is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public
// License along with this manual; if not, see
// <http://www.gnu.org/licenses/>.
// Package dl provides an interface to the POSIX runtime linker.
package dl
import (
"errors"
"sync"
"unsafe"
)
//#cgo LDFLAGS: -ldl
//#include <stdlib.h>
//#include <dlfcn.h>
import "C"
var HandleClosedError = errors.New("Handle is already closed")
type Flag int
// POSIX specifies these four flags to Open().
const (
// Relocations are performed at an implementation-defined
// time.
RTLD_LAZY Flag = C.RTLD_LAZY
// Relocations are performed when the object is loaded.
RTLD_NOW Flag = C.RTLD_NOW
// All symbols are available for relocation processing of
// other modules.
RTLD_GLOBAL Flag = C.RTLD_GLOBAL
// All symbols are not made available for relocation
// processing by other modules.
RTLD_LOCAL Flag = C.RTLD_LOCAL
)
type Handle struct {
c unsafe.Pointer
o int
l sync.RWMutex
}
// Open a shared object file, returning a Handle to it, or an error.
// If name is an empty string, then the returned handle is the global
// symbol table for the current process; if the name contains a slash,
// then it is interpretted as a pathname; otherwise, it is
// interpretted in an implementation-defined manner.
func Open(name string, flags Flag) (Handle, error) {
nameC := C.CString(name)
defer C.free(unsafe.Pointer(nameC))
if name == "" {
nameC = nil
}
dlerror()
ptr := C.dlopen(nameC, C.int(flags))
if ptr == nil {
return Handle{}, dlerror()
}
return Handle{c: ptr, o: 1}, nil
}
// Look up a symbol, and return a pointer to it.
//
// This returns uintptr instead of unsafe.Pointer so that code using
// dl cannot obtain unsafe.Pointers without importing the unsafe
// package explicitly.
func (h Handle) Sym(symbol string) (uintptr, error) {
h.l.RLock()
defer h.l.RUnlock()
if h.o == 0 {
return 0, HandleClosedError
}
symbolC := C.CString(symbol)
defer C.free(unsafe.Pointer(symbolC))
dlerror()
ptr := C.dlsym(h.c, symbolC)
if ptr == nil {
return 0, dlerror()
}
return uintptr(ptr), nil
}
// Close this handle on a shared object; decrementint the reference
// count; if the reference count drops below 0, then the object is
// unloaded.
func (h Handle) Close() error {
h.l.Lock()
defer h.l.Unlock()
if h.o == 0 {
return HandleClosedError
}
dlerror()
r := C.dlclose(h.c)
if r != 0 {
return dlerror()
}
if h.o == 1 {
h.o = 0
}
return nil
}
func dlerror() error {
strC := C.dlerror()
if strC == nil {
return nil
}
return errors.New(C.GoString(strC))
}
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