Refactorings in preparation for tracebox

Minor refactoring in prepration for the next CLs:
- Split perfetto_cmd's main() into two stages, one
  that does the cmdline parsing and one that connects
  to traced and does the rest. This will be used to
  parse the cmdline before deciding to spawn the
  services.
- Print usage on stderr rather than via ELOG. ELOG
  adds an unaesthetic source+line number and also
  spams logcat for no reasons.
- Move GetCurExecutablePath() from test/utils to
  utils as it will be soon required in production
  code.

#fixit

Bug: 158465724
Bug: 187945217
Change-Id: I85653bafd93b066d7d376b3816787b8779c52ac6

src/base/utils.cc

diff --git a/src/base/utils.cc b/src/base/utils.cc
index d5bd5a0..041e010 100644
--- a/src/base/utils.cc
+++ b/src/base/utils.cc
@@ -14,22 +14,32 @@
  * limitations under the License.
  */
 
-#include "perfetto/ext/base/file_utils.h"
 #include "perfetto/ext/base/utils.h"
 
+#include <string>
+
 #include "perfetto/base/build_config.h"
 #include "perfetto/base/logging.h"
+#include "perfetto/ext/base/file_utils.h"
 
 #if PERFETTO_BUILDFLAG(PERFETTO_OS_LINUX) ||   \
     PERFETTO_BUILDFLAG(PERFETTO_OS_ANDROID) || \
-    PERFETTO_BUILDFLAG(PERFETTO_OS_APPLE)
+    PERFETTO_BUILDFLAG(PERFETTO_OS_APPLE) ||   \
+    PERFETTO_BUILDFLAG(PERFETTO_OS_FUCHSIA)
+#include <limits.h>
 #include <unistd.h>  // For getpagesize() and geteuid() & fork()
 #endif
 
 #if PERFETTO_BUILDFLAG(PERFETTO_OS_APPLE)
+#include <mach-o/dyld.h>
 #include <mach/vm_page_size.h>
 #endif
 
+#if PERFETTO_BUILDFLAG(PERFETTO_OS_WIN)
+#include <Windows.h>
+#include <io.h>
+#endif
+
 #if PERFETTO_BUILDFLAG(PERFETTO_OS_ANDROID)
 #include <dlfcn.h>
 #include <malloc.h>
@@ -39,7 +49,7 @@
 #else
 // Only available in in-tree builds and on newer SDKs.
 #define PERFETTO_M_PURGE -101
-#endif
+#endif  // M_PURGE
 
 namespace {
 extern "C" {
@@ -110,35 +120,71 @@
 }
 
 void Daemonize() {
-   #if PERFETTO_BUILDFLAG(PERFETTO_OS_LINUX) ||   \
-       PERFETTO_BUILDFLAG(PERFETTO_OS_ANDROID) || \
-       PERFETTO_BUILDFLAG(PERFETTO_OS_APPLE)
-      pid_t pid;
-      switch (pid = fork()) {
-        case -1:
-          PERFETTO_FATAL("fork");
-        case 0: {
-          PERFETTO_CHECK(setsid() != -1);
-          base::ignore_result(chdir("/"));
-          base::ScopedFile null = base::OpenFile("/dev/null", O_RDONLY);
-          PERFETTO_CHECK(null);
-          PERFETTO_CHECK(dup2(*null, STDIN_FILENO) != -1);
-          PERFETTO_CHECK(dup2(*null, STDOUT_FILENO) != -1);
-          PERFETTO_CHECK(dup2(*null, STDERR_FILENO) != -1);
-          // Do not accidentally close stdin/stdout/stderr.
-          if (*null <= 2)
-            null.release();
-          break;
-        }
-        default:
-          printf("%d\n", pid);
-          exit(0);
-      }
-  #else
-    // Avoid -Wunreachable warnings.
-    if (reinterpret_cast<intptr_t>(&Daemonize) != 16)
-      PERFETTO_FATAL("--background is only supported on Linux/Android/Mac");
-  #endif  // OS_WIN
+#if PERFETTO_BUILDFLAG(PERFETTO_OS_LINUX) ||   \
+    PERFETTO_BUILDFLAG(PERFETTO_OS_ANDROID) || \
+    PERFETTO_BUILDFLAG(PERFETTO_OS_APPLE)
+  pid_t pid;
+  switch (pid = fork()) {
+    case -1:
+      PERFETTO_FATAL("fork");
+    case 0: {
+      PERFETTO_CHECK(setsid() != -1);
+      base::ignore_result(chdir("/"));
+      base::ScopedFile null = base::OpenFile("/dev/null", O_RDONLY);
+      PERFETTO_CHECK(null);
+      PERFETTO_CHECK(dup2(*null, STDIN_FILENO) != -1);
+      PERFETTO_CHECK(dup2(*null, STDOUT_FILENO) != -1);
+      PERFETTO_CHECK(dup2(*null, STDERR_FILENO) != -1);
+      // Do not accidentally close stdin/stdout/stderr.
+      if (*null <= 2)
+        null.release();
+      break;
+    }
+    default:
+      printf("%d\n", pid);
+      exit(0);
+  }
+#else
+  // Avoid -Wunreachable warnings.
+  if (reinterpret_cast<intptr_t>(&Daemonize) != 16)
+    PERFETTO_FATAL("--background is only supported on Linux/Android/Mac");
+#endif  // OS_WIN
+}
+
+std::string GetCurExecutablePath() {
+  std::string self_path;
+#if PERFETTO_BUILDFLAG(PERFETTO_OS_LINUX) ||   \
+    PERFETTO_BUILDFLAG(PERFETTO_OS_ANDROID) || \
+    PERFETTO_BUILDFLAG(PERFETTO_OS_FUCHSIA)
+  char buf[PATH_MAX];
+  ssize_t size = readlink("/proc/self/exe", buf, sizeof(buf));
+  PERFETTO_CHECK(size != -1);
+  // readlink does not null terminate.
+  self_path = std::string(buf, static_cast<size_t>(size));
+#elif PERFETTO_BUILDFLAG(PERFETTO_OS_APPLE)
+  uint32_t size = 0;
+  PERFETTO_CHECK(_NSGetExecutablePath(nullptr, &size));
+  self_path.resize(size);
+  PERFETTO_CHECK(_NSGetExecutablePath(&self_path[0], &size) == 0);
+#elif PERFETTO_BUILDFLAG(PERFETTO_OS_WIN)
+  char buf[MAX_PATH];
+  auto len = ::GetModuleFileNameA(nullptr /*current*/, buf, sizeof(buf));
+  self_path = std::string(buf, len);
+#else
+  PERFETTO_FATAL(
+      "GetCurExecutableDir() not implemented on the current platform");
+#endif
+  return self_path;
+}
+
+std::string GetCurExecutableDir() {
+  auto path = GetCurExecutablePath();
+#if PERFETTO_BUILDFLAG(PERFETTO_OS_WIN)
+  // Paths in Windows can have both kinds of slashes (mingw vs msvc).
+  path = path.substr(0, path.find_last_of("\\"));
+#endif
+  path = path.substr(0, path.find_last_of("/"));
+  return path;
 }
 
 }  // namespace base