dynamic linker is running for init

init is now built as a dynamic executable, so the dynamic linker has to
be able to run in the init process. However, since init is launched so
early, even /dev/* and /proc/* file systems are not mounted and thus
some APIs that rely on the paths do not work. The dynamic linker now
goes alternative path when it is running in the init process.

For example, /proc/self/exe is not read for the init since we always now
the path of the init (/init). Also, arc4random* APIs are not used since
the APIs rely on /dev/urandom. Linker now does not randomize library
loading order and addresses when running in the init process.

Bug: 80454183
Test: `adb reboot recovery; adb devices` shows the device ID
Change-Id: I29b6d70e4df5f7f690876126d5fe81258c1d3115

1 files changed, 17 insertions, 7 deletions

diff --git a/linker/linker_main.cpp b/linker/linker_main.cpp
index 1a0d1642b..a8741527e 100644
--- a/linker/linker_main.cpp
+++ b/linker/linker_main.cpp
@@ -197,12 +197,16 @@ extern "C" int __system_properties_init(void);
 static const char* get_executable_path() {
   static std::string executable_path;
   if (executable_path.empty()) {
-    char path[PATH_MAX];
-    ssize_t path_len = readlink("/proc/self/exe", path, sizeof(path));
-    if (path_len == -1 || path_len >= static_cast<ssize_t>(sizeof(path))) {
-      async_safe_fatal("readlink('/proc/self/exe') failed: %s", strerror(errno));
+    if (!is_init()) {
+      char path[PATH_MAX];
+      ssize_t path_len = readlink("/proc/self/exe", path, sizeof(path));
+      if (path_len == -1 || path_len >= static_cast<ssize_t>(sizeof(path))) {
+        async_safe_fatal("readlink('/proc/self/exe') failed: %s", strerror(errno));
+      }
+      executable_path = std::string(path, path_len);
+    } else {
+      executable_path = "/init";
     }
-    executable_path = std::string(path, path_len);
   }
 
   return executable_path.c_str();
@@ -288,8 +292,14 @@ static ElfW(Addr) linker_main(KernelArgumentBlock& args) {
   // Stat "/proc/self/exe" instead of executable_path because
   // the executable could be unlinked by this point and it should
   // not cause a crash (see http://b/31084669)
-  if (TEMP_FAILURE_RETRY(stat("/proc/self/exe", &file_stat)) != 0) {
-    async_safe_fatal("unable to stat \"/proc/self/exe\": %s", strerror(errno));
+  if (!is_init()) {
+    if (TEMP_FAILURE_RETRY(stat("/proc/self/exe", &file_stat)) != 0) {
+      async_safe_fatal("unable to stat \"/proc/self/exe\": %s", strerror(errno));
+    }
+  } else {
+    // /proc fs is not mounted when init starts. Therefore we can't use
+    // /proc/self/exe for init.
+    stat("/init", &file_stat);
   }
 
   const char* executable_path = get_executable_path();