Seperate GetSelfPath implementation for Blaze and Bazel

In Blaze, we keep using "/proc/self/exe", but in Bazel we resolve this symlink
to the actual Bazel binary.

This is essentially a rollback of
bazelbuild@d79ec03
only for Bazel, because it solved an issue that rare in Bazel,
but it's preventing users from running Bazel inside a Linux docker container on Apple Silicon machines.

Fixes bazelbuild#15076

Closes bazelbuild#14391

RELNOTES: None
PiperOrigin-RevId: 441198110

Author: meteorcloudy

src/main/cpp/BUILD

@@ -36,6 +36,7 @@ cc_library(
         "//conditions:default": [
             "blaze_util_linux.cc",
             "blaze_util_posix.cc",
+            "get_self_path_linux.cc",
         ],
     }),
     hdrs = [

src/main/cpp/blaze_util_linux.cc

@@ -82,13 +82,6 @@ void WarnFilesystemType(const blaze_util::Path &output_base) {
   }
 }
 
-string GetSelfPath(const char* argv0) {
-  // The file to which this symlink points could change contents or go missing
-  // concurrent with execution of the Bazel client, so we don't eagerly resolve
-  // it.
-  return "/proc/self/exe";
-}
-
 uint64_t GetMillisecondsMonotonic() {
   struct timespec ts = {};
   clock_gettime(CLOCK_MONOTONIC, &ts);

src/main/cpp/get_self_path_linux.cc

@@ -0,0 +1,44 @@
+// Copyright 2022 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <unistd.h>
+#include <limits.h>
+
+#include "src/main/cpp/blaze_util_platform.h"
+#include "src/main/cpp/util/errors.h"
+#include "src/main/cpp/util/exit_code.h"
+#include "src/main/cpp/util/logging.h"
+
+namespace blaze {
+
+using blaze_util::GetLastErrorString;
+using std::string;
+
+string GetSelfPath(const char* argv0) {
+  char buffer[PATH_MAX] = {};
+  ssize_t bytes = readlink("/proc/self/exe", buffer, sizeof(buffer));
+  if (bytes == sizeof(buffer)) {
+    // symlink contents truncated
+    bytes = -1;
+    errno = ENAMETOOLONG;
+  }
+  if (bytes == -1) {
+    BAZEL_DIE(blaze_exit_code::INTERNAL_ERROR)
+        << "error reading /proc/self/exe: " << GetLastErrorString();
+  }
+  buffer[bytes] = '\0';  // readlink does not NUL-terminate
+  return string(buffer);
+}
+
+}  // namespace blaze