libdebuggerd: fix process uptime.

I was here because we have a case where timeout(1) kills logcat, but
debuggerd alleges that the process that was killed had started less than
a second ago. I'm not sure this is the problem there, but I did notice
that far too many tombstones were claiming improbably short process
uptimes. It turns out that the code was measuring the *thread* uptime,
not the *process* uptime.

Also simplify the code a bit by switching to sysinfo(2) rather than
reading a file.

Test: manual, plus the existing unit test
Change-Id: Ie2810b1d5777ad9182be92bfb3f60795dc978b24

debuggerd/libdebuggerd/tombstone_proto.cpp

@@ -28,6 +28,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/mman.h>
+#include <sys/sysinfo.h>
 #include <time.h>
 
 #include <memory>
@@ -596,14 +597,6 @@ static void dump_tags_around_fault_addr(Signal* signal, const Tombstone& tombsto
   }
 }
 
-static std::optional<uint64_t> read_uptime_secs() {
-  std::string uptime;
-  if (!android::base::ReadFileToString("/proc/uptime", &uptime)) {
-    return {};
-  }
-  return strtoll(uptime.c_str(), nullptr, 10);
-}
-
 void engrave_tombstone_proto(Tombstone* tombstone, unwindstack::Unwinder* unwinder,
                              const std::map<pid_t, ThreadInfo>& threads, pid_t target_thread,
                              const ProcessInfo& process_info, const OpenFilesList* open_files) {
@@ -614,28 +607,24 @@ void engrave_tombstone_proto(Tombstone* tombstone, unwindstack::Unwinder* unwind
   result.set_revision(android::base::GetProperty("ro.revision", "unknown"));
   result.set_timestamp(get_timestamp());
 
-  std::optional<uint64_t> system_uptime = read_uptime_secs();
-  if (system_uptime) {
-    android::procinfo::ProcessInfo proc_info;
-    std::string error;
-    if (android::procinfo::GetProcessInfo(target_thread, &proc_info, &error)) {
-      uint64_t starttime = proc_info.starttime / sysconf(_SC_CLK_TCK);
-      result.set_process_uptime(*system_uptime - starttime);
-    } else {
-      async_safe_format_log(ANDROID_LOG_ERROR, LOG_TAG, "failed to read process info: %s",
-                            error.c_str());
-    }
-  } else {
-    async_safe_format_log(ANDROID_LOG_ERROR, LOG_TAG, "failed to read /proc/uptime: %s",
-                          strerror(errno));
-  }
-
   const ThreadInfo& main_thread = threads.at(target_thread);
   result.set_pid(main_thread.pid);
   result.set_tid(main_thread.tid);
   result.set_uid(main_thread.uid);
   result.set_selinux_label(main_thread.selinux_label);
 
+  struct sysinfo si;
+  sysinfo(&si);
+  android::procinfo::ProcessInfo proc_info;
+  std::string error;
+  if (android::procinfo::GetProcessInfo(main_thread.pid, &proc_info, &error)) {
+    uint64_t starttime = proc_info.starttime / sysconf(_SC_CLK_TCK);
+    result.set_process_uptime(si.uptime - starttime);
+  } else {
+    async_safe_format_log(ANDROID_LOG_ERROR, LOG_TAG, "failed to read process info: %s",
+                          error.c_str());
+  }
+
   auto cmd_line = result.mutable_command_line();
   for (const auto& arg : main_thread.command_line) {
     *cmd_line->Add() = arg;

debuggerd/seccomp_policy/crash_dump.arm.policy

@@ -20,6 +20,7 @@ getdents64: 1
 faccessat: 1
 recvmsg: 1
 recvfrom: 1
+sysinfo: 1
 process_vm_readv: 1
 tgkill: 1
 rt_sigprocmask: 1

debuggerd/seccomp_policy/crash_dump.arm64.policy

@@ -19,6 +19,7 @@ getdents64: 1
 faccessat: 1
 recvmsg: 1
 recvfrom: 1
+sysinfo: 1
 process_vm_readv: 1
 tgkill: 1
 rt_sigprocmask: 1

debuggerd/seccomp_policy/crash_dump.policy.def

@@ -25,6 +25,7 @@ getdents64: 1
 faccessat: 1
 recvmsg: 1
 recvfrom: 1
+sysinfo: 1
 
 process_vm_readv: 1
 

debuggerd/seccomp_policy/crash_dump.x86.policy

@@ -20,6 +20,7 @@ getdents64: 1
 faccessat: 1
 recvmsg: 1
 recvfrom: 1
+sysinfo: 1
 process_vm_readv: 1
 tgkill: 1
 rt_sigprocmask: 1

debuggerd/seccomp_policy/crash_dump.x86_64.policy

@@ -19,6 +19,7 @@ getdents64: 1
 faccessat: 1
 recvmsg: 1
 recvfrom: 1
+sysinfo: 1
 process_vm_readv: 1
 tgkill: 1
 rt_sigprocmask: 1