plugin: new package for loading plugins

Includes a linux implementation.

Change-Id: Iacc2ed7da760ae9deebc928adf2b334b043b07ec
Reviewed-on: https://go-review.googlesource.com/27823
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 51 insertions, 0 deletions

diff --git a/src/runtime/plugin.go b/src/runtime/plugin.go
index f5f3aa2e5b..2e01650824 100644
--- a/src/runtime/plugin.go
+++ b/src/runtime/plugin.go
@@ -4,6 +4,57 @@
 
 package runtime
 
+import "unsafe"
+
+//go:linkname plugin_lastmoduleinit plugin.lastmoduleinit
+func plugin_lastmoduleinit() map[string]interface{} {
+	md := firstmoduledata.next
+	if md == nil {
+		throw("runtime: no plugin module data")
+	}
+	for md.next != nil {
+		md = md.next
+	}
+	if md.typemap != nil {
+		throw("runtime: plugin already initialized")
+	}
+
+	// Initialize the freshly loaded module.
+	typelinksinit()
+	md.gcdatamask = progToPointerMask((*byte)(unsafe.Pointer(md.gcdata)), md.edata-md.data)
+	md.gcbssmask = progToPointerMask((*byte)(unsafe.Pointer(md.gcbss)), md.ebss-md.bss)
+
+	lock(&ifaceLock)
+	for _, i := range md.itablinks {
+		additab(i, true, false)
+	}
+	unlock(&ifaceLock)
+
+	// Build a map of symbol names to symbols. Here in the runtime
+	// we fill out the first word of the interface, the type. We
+	// pass these zero value interfaces to the plugin package,
+	// where the symbol value is filled in (usually via cgo).
+	//
+	// Because functions are handled specially in the plugin package,
+	// function symbol names are prefixed here with '.' to avoid
+	// a dependency on the reflect package.
+	syms := make(map[string]interface{}, len(md.ptab))
+	for _, ptab := range md.ptab {
+		symName := resolveNameOff(unsafe.Pointer(md.types), ptab.name)
+		t := (*_type)(unsafe.Pointer(md.types)).typeOff(ptab.typ)
+		var val interface{}
+		valp := (*[2]unsafe.Pointer)(unsafe.Pointer(&val))
+		(*valp)[0] = unsafe.Pointer(t)
+
+		name := symName.name()
+		if t.kind&kindMask == kindFunc {
+			name = "." + name
+		}
+		syms[name] = val
+	}
+	return syms
+}
+
 // A ptabEntry is generated by the compiler for each exported function
 // and global variable in the main package of a plugin. It is used to
 // initialize the plugin module's symbol map.