4 files changed, 50 insertions, 0 deletions
diff --git a/src/libexpr/local.mk b/src/libexpr/local.mk
index b3b4086916ef..75a0e185e369 100644
--- a/src/libexpr/local.mk
+++ b/src/libexpr/local.mk
@@ -8,6 +8,8 @@ libexpr_SOURCES := $(wildcard $(d)/*.cc) $(d)/lexer-tab.cc $(d)/parser-tab.cc
 
 libexpr_LIBS = libutil libstore libformat
 
+libexpr_LDFLAGS = -ldl
+
 # The dependency on libgc must be propagated (i.e. meaning that
 # programs/libraries that use libexpr must explicitly pass -lgc),
 # because inline functions in libexpr's header files call libgc.
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 366911b54dcf..ff82f36b52f7 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -15,6 +15,7 @@
 
 #include <algorithm>
 #include <cstring>
+#include <dlfcn.h>
 
 
 namespace nix {
@@ -129,6 +130,46 @@ static void prim_scopedImport(EvalState & state, const Pos & pos, Value * * args
 }
 
 
+/* Want reasonable symbol names, so extern C */
+/* !!! Should we pass the Pos or the file name too? */
+extern "C" typedef void (*ValueInitializer)(EvalState & state, Value & v);
+
+/* Load a ValueInitializer from a dso and return whatever it initializes */
+static void prim_importNative(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    PathSet context;
+    Path path = state.coerceToPath(pos, *args[0], context);
+
+    try {
+        realiseContext(context);
+    } catch (InvalidPathError & e) {
+        throw EvalError(format("cannot import `%1%', since path `%2%' is not valid, at %3%")
+            % path % e.path % pos);
+    }
+
+    string sym = state.forceStringNoCtx(*args[1], pos);
+
+    void *handle = dlopen(path.c_str(), RTLD_LAZY | RTLD_LOCAL);
+    if (!handle)
+        throw EvalError(format("could not open `%1%': %2%") % path % dlerror());
+
+    dlerror();
+    ValueInitializer func = (ValueInitializer) dlsym(handle, sym.c_str());
+    if(!func) {
+        char *message = dlerror();
+        if (message)
+            throw EvalError(format("could not load symbol `%1%' from `%2%': %3%") % sym % path % message);
+        else
+            throw EvalError(format("symbol `%1%' from `%2%' resolved to NULL when a function pointer was expected")
+                    % sym % path);
+    }
+
+    (func)(state, v);
+
+    /* We don't dlclose because v may be a primop referencing a function in the shared object file */
+}
+
+
 /* Return a string representing the type of the expression. */
 static void prim_typeOf(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
@@ -1327,6 +1368,8 @@ void EvalState::createBaseEnv()
     mkApp(v, *baseEnv.values[baseEnvDispl - 1], *v2);
     forceValue(v);
     addConstant("import", v);
+    if (settings.enableImportNative)
+        addPrimOp("__importNative", 2, prim_importNative);
     addPrimOp("__typeOf", 1, prim_typeOf);
     addPrimOp("isNull", 1, prim_isNull);
     addPrimOp("__isFunction", 1, prim_isFunction);
diff --git a/src/libstore/globals.cc b/src/libstore/globals.cc
index 180344e336b0..5d359e12811f 100644
--- a/src/libstore/globals.cc
+++ b/src/libstore/globals.cc
@@ -61,6 +61,7 @@ Settings::Settings()
     envKeepDerivations = false;
     lockCPU = getEnv("NIX_AFFINITY_HACK", "1") == "1";
     showTrace = false;
+    enableImportNative = false;
 }
 
 
@@ -148,6 +149,7 @@ void Settings::update()
     get(sshSubstituterHosts, "ssh-substituter-hosts");
     get(useSshSubstituter, "use-ssh-substituter");
     get(logServers, "log-servers");
+    get(enableImportNative, "allow-arbitrary-code-during-evaluation");
 
     string subs = getEnv("NIX_SUBSTITUTERS", "default");
     if (subs == "default") {
diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index 65a6c388b8a6..8dd59a9c7967 100644
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -200,6 +200,9 @@ struct Settings {
     /* A list of URL prefixes that can return Nix build logs. */
     Strings logServers;
 
+    /* Whether the importNative primop should be enabled */
+    bool enableImportNative;
+
 private:
     SettingsMap settings, overrides;