Added user API to specify manually loaded library handle (gh-14).

arch/common/init.c.tpl

@@ -41,6 +41,7 @@ extern "C" {
 #define LAZY_LOAD $lazy_load
 
 static void *lib_handle;
+static int do_dlclose;
 static int is_lib_loading;
 
 #if ! NO_DLOPEN
@@ -59,13 +60,14 @@ static void *load_library() {
   CHECK(lib_handle, "failed to load library via dlopen: %s", dlerror());
 #endif
 
+  do_dlclose = 1;
   is_lib_loading = 0;
 
   return lib_handle;
 }
 
 static void __attribute__((destructor)) unload_lib() {
-  if(lib_handle)
+  if(do_dlclose && lib_handle)
     dlclose(lib_handle);
 }
 #endif
@@ -94,14 +96,20 @@ void _${lib_suffix}_tramp_resolve(int i) {
 
   void *h = 0;
 #if NO_DLOPEN
-// Library with implementations has already been loaded.
-// If shim symbols are hidden we should search for first available definition of symbol
-// in library list, otherwise look for next available definition
-# ifdef IMPLIB_HIDDEN_SHIMS
-  h = RTLD_DEFAULT;
-# else
-  h = RTLD_NEXT;
-# endif
+  // Library with implementations must have already been loaded.
+  if (lib_handle) {
+    // User has specified loaded library
+    h = lib_handle;
+  } else {
+    // User hasn't provided us the loaded library so search the global namespace.
+    // If shim symbols are hidden we should search for first available definition of symbol
+    // in library list, otherwise look for next available definition
+#   ifdef IMPLIB_HIDDEN_SHIMS
+    h = RTLD_DEFAULT;
+#   else
+    h = RTLD_NEXT;
+#   endif
+  }
 #else
   h = load_library();
   CHECK(h, "failed to resolve symbol '%s', library failed to load", sym_names[i]);
@@ -119,11 +127,18 @@ void _${lib_suffix}_tramp_resolve_all(void) {
     _${lib_suffix}_tramp_resolve(i);
 }
 
+// Allows user to specify manually loaded implementation library.
+void _${lib_suffix}_tramp_set_handle(void *handle) {
+  lib_handle = handle;
+  do_dlclose = 0;
+}
+
 // Resets all resolved symbols. This is needed in case
 // client code wants to reload interposed library multiple times.
 void _${lib_suffix}_tramp_reset(void) {
   memset(_${lib_suffix}_tramp_table, 0, SYM_COUNT * sizeof(_${lib_suffix}_tramp_table[0]));
   lib_handle = 0;
+  do_dlclose = 0;
 }
 
 #ifdef __cplusplus

scripts/travis.sh

@@ -36,3 +36,4 @@ tests/verbose/run.sh $ARCH
 tests/no_dlopen/run.sh $ARCH
 tests/multiple-dlopens/run.sh $ARCH
 tests/multiple-dlopens-2/run.sh $ARCH
+tests/multiple-dlopens-3/run.sh $ARCH

tests/multiple-dlopens-2/main.c

@@ -33,21 +33,16 @@ void *my_load_library(const char *name) {
   return handle;
 }
 
-void my_unload_library() {
-  dlclose(handle);
-  handle = 0;
-  assert(dlopen("libinterposed.so", RTLD_NOLOAD) == 0);
-
-  extern void _libinterposed_so_tramp_reset(void);
-  _libinterposed_so_tramp_reset();
-}
-
 int main() {
-  test();
-  my_unload_library();
+  extern void _libinterposed_so_tramp_reset(void);
 
-  test();
-  my_unload_library();
+  for (int i = 0; i < 2; ++i) {
+    test();
+    dlclose(handle);
+    handle = 0;
+    assert(dlopen("libinterposed.so", RTLD_NOLOAD) == 0);
+    _libinterposed_so_tramp_reset();
+  }
 
   return 0;
 }

tests/multiple-dlopens-3/interposed.c

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2022 Yury Gribov
+ *
+ * The MIT License (MIT)
+ * 
+ * Use of this source code is governed by MIT license that can be
+ * found in the LICENSE.txt file.
+ */
+
+#include <stdio.h>
+#include "interposed.h"
+
+__attribute__((visibility("default")))
+int foo(int x, float y) {
+  printf("Calling foo from libtest: %d %g\n", x, y);
+  return 0xf00;
+}
+
+__attribute__((visibility("default")))
+int bar(int x, int y, int z) {
+  printf("Calling bar from libtest: %d %d %d\n", x, y, z);
+  return 0xba7;
+}

tests/multiple-dlopens-3/interposed.h

@@ -0,0 +1,16 @@
+/*
+ * Copyright 2022 Yury Gribov
+ *
+ * The MIT License (MIT)
+ * 
+ * Use of this source code is governed by MIT license that can be
+ * found in the LICENSE.txt file.
+ */
+
+#ifndef INTERPOSED_H
+#define INTERPOSED_H
+
+extern int foo(int x, float y);
+extern int bar(int x, int y, int z);
+
+#endif

tests/multiple-dlopens-3/main.c

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2022 Yury Gribov
+ *
+ * The MIT License (MIT)
+ * 
+ * Use of this source code is governed by MIT license that can be
+ * found in the LICENSE.txt file.
+ */
+
+#include <dlfcn.h>
+#include <stdio.h>
+#include <assert.h>
+
+#include "interposed.h"
+
+void test() {
+  int x, y;
+  // Slow path
+  x = foo(25, 0.5),
+  y = bar(11, 22, 33);
+  printf("Results: %x %x\n", x, y);
+  // Fast path
+  x = foo(35, 0.25);
+  y = bar(44, 55, 66);
+  printf("Results: %x %x\n", x, y);
+}
+
+int main() {
+  extern void _libinterposed_so_tramp_set_handle(void *handle);
+  extern void _libinterposed_so_tramp_reset(void);
+
+  for (int i = 0; i < 2; ++i) {
+    void *h = dlopen("libinterposed.so", RTLD_LOCAL | RTLD_LAZY);
+    _libinterposed_so_tramp_set_handle(h);
+
+    test();
+
+    dlclose(h);
+    assert(dlopen("libinterposed.so", RTLD_NOLOAD) == 0);
+    _libinterposed_so_tramp_reset();
+  }
+
+  return 0;
+}

tests/multiple-dlopens-3/run.sh

@@ -0,0 +1,42 @@
+#!/bin/sh
+
+# Copyright 2022 Yury Gribov
+#
+# The MIT License (MIT)
+# 
+# Use of this source code is governed by MIT license that can be
+# found in the LICENSE.txt file.
+
+# This is a test for manual loading of destination library (--no-dlopen flag).
+# Run it like
+#   ./run.sh ARCH
+# where ARCH stands for any supported arch (arm, x86_64, etc., see `implib-gen -h' for full list).
+# Note that you may need to install qemu-user for respective platform
+# (i386 also needs gcc-multilib).
+
+set -eu
+
+cd $(dirname $0)
+
+if test -n "${1:-}"; then
+  ARCH="$1"
+fi
+
+. ../common.sh
+
+CFLAGS="-g -O2 $CFLAGS"
+LIBS='-ldl'
+
+# Build shlib to test against
+$CC $CFLAGS -shared -fPIC interposed.c -o libinterposed.so
+
+# Prepare implib
+${PYTHON:-} ../../implib-gen.py -q --target $TARGET --no-dlopen libinterposed.so
+
+# Build app
+$CC $CFLAGS -fPIE main.c libinterposed.so.tramp.S libinterposed.so.init.c $LIBS
+
+LD_LIBRARY_PATH=.:${LD_LIBRARY_PATH:-} $INTERP ./a.out > a.out.log
+diff test.ref a.out.log
+
+echo SUCCESS

tests/multiple-dlopens-3/test.ref

@@ -0,0 +1,12 @@
+Calling foo from libtest: 25 0.5
+Calling bar from libtest: 11 22 33
+Results: f00 ba7
+Calling foo from libtest: 35 0.25
+Calling bar from libtest: 44 55 66
+Results: f00 ba7
+Calling foo from libtest: 25 0.5
+Calling bar from libtest: 11 22 33
+Results: f00 ba7
+Calling foo from libtest: 35 0.25
+Calling bar from libtest: 44 55 66
+Results: f00 ba7

tests/multiple-dlopens/main.c

@@ -28,17 +28,13 @@ void test() {
 extern void _libinterposed_so_tramp_reset(void);
 
 int main() {
-  void *h = dlopen("libinterposed.so", RTLD_GLOBAL | RTLD_LAZY);
-  test();
-  dlclose(h);
-  assert(dlopen("libinterposed.so", RTLD_NOLOAD) == 0);
-  _libinterposed_so_tramp_reset();
-
-  h = dlopen("libinterposed.so", RTLD_GLOBAL | RTLD_LAZY);
-  test();
-  dlclose(h);
-  assert(dlopen("libinterposed.so", RTLD_NOLOAD) == 0);
-  _libinterposed_so_tramp_reset();
+  for (int i = 0; i < 2; ++i) {
+    void *h = dlopen("libinterposed.so", RTLD_GLOBAL | RTLD_LAZY);
+    test();
+    dlclose(h);
+    assert(dlopen("libinterposed.so", RTLD_NOLOAD) == 0);
+    _libinterposed_so_tramp_reset();
+  }
 
   return 0;
 }