Merge "Make it possible for code to query the dynamic linker's default search path."

libdl/libdl.c

@@ -15,6 +15,8 @@
  */
 
 #include <dlfcn.h>
+#include <stdlib.h>
+
 /* These are stubs for functions that are actually defined
  * in the dynamic linker (dlfcn.c), and hijacked at runtime.
  */
@@ -24,6 +26,7 @@ void *dlsym(void *handle, const char *symbol) { return 0; }
 int dladdr(const void *addr, Dl_info *info) { return 0; }
 int dlclose(void *handle) { return 0; }
 
+void android_get_LD_LIBRARY_PATH(char* buffer, size_t buffer_size) { }
 void android_update_LD_LIBRARY_PATH(const char* ld_library_path) { }
 
 #if defined(__arm__)

linker/dlfcn.cpp

@@ -54,6 +54,11 @@ const char* dlerror() {
   return old_value;
 }
 
+void android_get_LD_LIBRARY_PATH(char* buffer, size_t buffer_size) {
+  ScopedPthreadMutexLocker locker(&gDlMutex);
+  do_android_get_LD_LIBRARY_PATH(buffer, buffer_size);
+}
+
 void android_update_LD_LIBRARY_PATH(const char* ld_library_path) {
   ScopedPthreadMutexLocker locker(&gDlMutex);
   do_android_update_LD_LIBRARY_PATH(ld_library_path);
@@ -143,20 +148,6 @@ int dlclose(void* handle) {
   return do_dlclose(reinterpret_cast<soinfo*>(handle));
 }
 
-#if defined(__arm__)
-//   0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888 8888888
-//   0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012 3456789
-#define ANDROID_LIBDL_STRTAB \
-    "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0dl_iterate_phdr\0dl_unwind_find_exidx\0"
-#elif defined(__aarch64__) || defined(__i386__) || defined(__mips__) || defined(__x86_64__)
-//   0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667
-//   0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890
-#define ANDROID_LIBDL_STRTAB \
-    "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0dl_iterate_phdr\0"
-#else
-#error Unsupported architecture. Only aarch64, arm, mips, x86, and x86_64 are presently supported.
-#endif
-
 // name_offset: starting index of the name in libdl_info.strtab
 #define ELF32_SYM_INITIALIZER(name_offset, value, shndx) \
     { name_offset, \
@@ -182,47 +173,55 @@ int dlclose(void* handle) {
 #  define ELF_SYM_INITIALIZER ELF32_SYM_INITIALIZER
 #endif
 
+#if defined(__arm__)
+  // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1
+  // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1
+#  define ANDROID_LIBDL_STRTAB \
+    "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_iterate_phdr\0dl_unwind_find_exidx\0"
+#elif defined(__aarch64__) || defined(__i386__) || defined(__mips__) || defined(__x86_64__)
+  // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1
+  // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1
+#  define ANDROID_LIBDL_STRTAB \
+    "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_iterate_phdr\0"
+#else
+#  error Unsupported architecture. Only aarch64, arm, mips, x86, and x86_64 are presently supported.
+#endif
+
 static Elf_Sym gLibDlSymtab[] = {
   // Total length of libdl_info.strtab, including trailing 0.
   // This is actually the STH_UNDEF entry. Technically, it's
   // supposed to have st_name == 0, but instead, it points to an index
   // in the strtab with a \0 to make iterating through the symtab easier.
   ELF_SYM_INITIALIZER(sizeof(ANDROID_LIBDL_STRTAB) - 1, NULL, 0),
-  ELF_SYM_INITIALIZER( 0, &dlopen, 1),
+  ELF_SYM_INITIALIZER(  0, &dlopen, 1),
-  ELF_SYM_INITIALIZER( 7, &dlclose, 1),
+  ELF_SYM_INITIALIZER(  7, &dlclose, 1),
-  ELF_SYM_INITIALIZER(15, &dlsym, 1),
+  ELF_SYM_INITIALIZER( 15, &dlsym, 1),
-  ELF_SYM_INITIALIZER(21, &dlerror, 1),
+  ELF_SYM_INITIALIZER( 21, &dlerror, 1),
-  ELF_SYM_INITIALIZER(29, &dladdr, 1),
+  ELF_SYM_INITIALIZER( 29, &dladdr, 1),
-  ELF_SYM_INITIALIZER(36, &android_update_LD_LIBRARY_PATH, 1),
+  ELF_SYM_INITIALIZER( 36, &android_update_LD_LIBRARY_PATH, 1),
-  ELF_SYM_INITIALIZER(67, &dl_iterate_phdr, 1),
+  ELF_SYM_INITIALIZER( 67, &android_get_LD_LIBRARY_PATH, 1),
+  ELF_SYM_INITIALIZER( 95, &dl_iterate_phdr, 1),
 #if defined(__arm__)
-  ELF_SYM_INITIALIZER(83, &dl_unwind_find_exidx, 1),
+  ELF_SYM_INITIALIZER(111, &dl_unwind_find_exidx, 1),
 #endif
 };
 
 // Fake out a hash table with a single bucket.
-// A search of the hash table will look through
-// gLibDlSymtab starting with index [1], then
-// use gLibDlChains to find the next index to
-// look at.  gLibDlChains should be set up to
-// walk through every element in gLibDlSymtab,
-// and then end with 0 (sentinel value).
 //
-// That is, gLibDlChains should look like
+// A search of the hash table will look through gLibDlSymtab starting with index 1, then
-// { 0, 2, 3, ... N, 0 } where N is the number
+// use gLibDlChains to find the next index to look at. gLibDlChains should be set up to
-// of actual symbols, or nelems(gLibDlSymtab)-1
+// walk through every element in gLibDlSymtab, and then end with 0 (sentinel value).
-// (since the first element of gLibDlSymtab is not
-// a real symbol).
 //
-// (see soinfo_elf_lookup())
+// That is, gLibDlChains should look like { 0, 2, 3, ... N, 0 } where N is the number
+// of actual symbols, or nelems(gLibDlSymtab)-1 (since the first element of gLibDlSymtab is not
+// a real symbol). (See soinfo_elf_lookup().)
 //
-// Note that adding any new symbols here requires
+// Note that adding any new symbols here requires stubbing them out in libdl.
-// stubbing them out in libdl.
 static unsigned gLibDlBuckets[1] = { 1 };
 #if defined(__arm__)
-static unsigned gLibDlChains[9] = { 0, 2, 3, 4, 5, 6, 7, 8, 0 };
+static unsigned gLibDlChains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
 #else
-static unsigned gLibDlChains[8] = { 0, 2, 3, 4, 5, 6, 7, 0 };
+static unsigned gLibDlChains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 0 };
 #endif
 
 // This is used by the dynamic linker. Every process gets these symbols for free.

linker/linker.cpp

@@ -50,13 +50,6 @@
 #include "linker_environ.h"
 #include "linker_phdr.h"
 
-/* Assume average path length of 64 and max 8 paths */
-#define LDPATH_BUFSIZE 512
-#define LDPATH_MAX 8
-
-#define LDPRELOAD_BUFSIZE 512
-#define LDPRELOAD_MAX 8
-
 /* >>> IMPORTANT NOTE - READ ME BEFORE MODIFYING <<<
  *
  * Do NOT use malloc() and friends or pthread_*() code here.
@@ -91,7 +84,7 @@ static soinfo* solist = &libdl_info;
 static soinfo* sonext = &libdl_info;
 static soinfo* somain; /* main process, always the one after libdl_info */
 
-static const char* const gSoPaths[] = {
+static const char* const gDefaultLdPaths[] = {
 #if defined(__LP64__)
   "/vendor/lib64",
   "/system/lib64",
@@ -102,6 +95,12 @@ static const char* const gSoPaths[] = {
   NULL
 };
 
+#define LDPATH_BUFSIZE (LDPATH_MAX*64)
+#define LDPATH_MAX 8
+
+#define LDPRELOAD_BUFSIZE (LDPRELOAD_MAX*64)
+#define LDPRELOAD_MAX 8
+
 static char gLdPathsBuffer[LDPATH_BUFSIZE];
 static const char* gLdPaths[LDPATH_MAX + 1];
 
@@ -708,7 +707,7 @@ static int open_library(const char* name) {
   // Otherwise we try LD_LIBRARY_PATH first, and fall back to the built-in well known paths.
   int fd = open_library_on_path(name, gLdPaths);
   if (fd == -1) {
-    fd = open_library_on_path(name, gSoPaths);
+    fd = open_library_on_path(name, gDefaultLdPaths);
   }
   return fd;
 }
@@ -828,6 +827,10 @@ static int soinfo_unload(soinfo* si) {
   return 0;
 }
 
+void do_android_get_LD_LIBRARY_PATH(char* buffer, size_t buffer_size) {
+  snprintf(buffer, buffer_size, "%s:%s", gDefaultLdPaths[0], gDefaultLdPaths[1]);
+}
+
 void do_android_update_LD_LIBRARY_PATH(const char* ld_library_path) {
   if (!get_AT_SECURE()) {
     parse_LD_LIBRARY_PATH(ld_library_path);

linker/linker.h

@@ -196,6 +196,7 @@ struct soinfo {
 
 extern soinfo libdl_info;
 
+void do_android_get_LD_LIBRARY_PATH(char*, size_t);
 void do_android_update_LD_LIBRARY_PATH(const char* ld_library_path);
 soinfo* do_dlopen(const char* name, int flags);
 int do_dlclose(soinfo* si);