[Backtracing] Support specifying a hard-coded path for swift-backtrace.

Add a way to disable dynamic lookup of the backtracer path, for situations
where a hard-coded path makes more sense.

rdar://107360391

Author: al45tair

stdlib/cmake/modules/StdlibOptions.cmake

@@ -234,3 +234,8 @@ option(SWIFT_STDLIB_CONCURRENCY_TRACING
 option(SWIFT_STDLIB_USE_RELATIVE_PROTOCOL_WITNESS_TABLES
        "Use relative protocol witness tables"
        FALSE)
+
+set(SWIFT_RUNTIME_FIXED_BACKTRACER_PATH "" CACHE STRING
+  "If set, provides a fixed path to the swift-backtrace binary.  This
+   will disable dynamic determination of the path and will also disable
+   the setting in SWIFT_BACKTRACE.")

stdlib/public/runtime/Backtrace.cpp

@@ -166,12 +166,25 @@ static_assert((SWIFT_BACKTRACE_ENVIRONMENT_SIZE % SWIFT_PAGE_SIZE) == 0,
 
 #if _WIN32
 #pragma section(SWIFT_BACKTRACE_SECTION, read, write)
+
+#if defined(SWIFT_RUNTIME_FIXED_BACKTRACER_PATH)
+const WCHAR swiftBacktracePath[] = L"" SWIFT_RUNTIME_FIXED_BACKTRACER_PATH;
+#else
 __declspec(allocate(SWIFT_BACKTRACE_SECTION)) WCHAR swiftBacktracePath[SWIFT_BACKTRACE_BUFFER_SIZE];
+#endif // !defined(SWIFT_RUNTIME_FIXED_BACKTRACER_PATH)
+
 __declspec(allocate(SWIFT_BACKTRACE_SECTION)) CHAR swiftBacktraceEnv[SWIFT_BACKTRACE_ENVIRONMENT_SIZE];
+
 #elif defined(__linux__) || TARGET_OS_OSX
+
+#if defined(SWIFT_RUNTIME_FIXED_BACKTRACER_PATH)
+const char swiftBacktracePath[] = SWIFT_RUNTIME_FIXED_BACKTRACER_PATH;
+#else
 char swiftBacktracePath[SWIFT_BACKTRACE_BUFFER_SIZE] __attribute__((section(SWIFT_BACKTRACE_SECTION), aligned(SWIFT_PAGE_SIZE)));
+#endif // !defined(SWIFT_RUNTIME_FIXED_BACKTRACER_PATH
+
 char swiftBacktraceEnv[SWIFT_BACKTRACE_ENVIRONMENT_SIZE] __attribute__((section(SWIFT_BACKTRACE_SECTION), aligned(SWIFT_PAGE_SIZE)));
-#endif
+#endif // defined(__linux__) || TARGET_OS_OSX
 
 void _swift_backtraceSetupEnvironment();
 
@@ -314,6 +327,7 @@ BacktraceInitializer::BacktraceInitializer() {
       _swift_backtraceSettings.preset = Preset::Full;
   }
 
+#if !defined(SWIFT_RUNTIME_FIXED_BACKTRACER_PATH)
   if (_swift_backtraceSettings.enabled == OnOffTty::On
       && !_swift_backtraceSettings.swiftBacktracePath) {
     _swift_backtraceSettings.swiftBacktracePath
@@ -327,6 +341,7 @@ BacktraceInitializer::BacktraceInitializer() {
       _swift_backtraceSettings.enabled = OnOffTty::Off;
     }
   }
+#endif
 
   if (_swift_backtraceSettings.enabled == OnOffTty::On) {
     // Copy the path to swift-backtrace into swiftBacktracePath, then write
@@ -339,6 +354,7 @@ BacktraceInitializer::BacktraceInitializer() {
     if (_swift_backtraceSettings.algorithm == UnwindAlgorithm::Auto)
       _swift_backtraceSettings.algorithm = UnwindAlgorithm::Precise;
 
+#if !defined(SWIFT_RUNTIME_FIXED_BACKTRACER_PATH)
     int len = ::MultiByteToWideChar(CP_UTF8, MB_ERR_INVALID_CHARS,
                                     _swift_backtraceSettings.swiftBacktracePath, -1,
                                     swiftBacktracePath,
@@ -359,6 +375,7 @@ BacktraceInitializer::BacktraceInitializer() {
                      ::GetLastError());
       _swift_backtraceSettings.enabled = OnOffTty::Off;
     }
+#endif // !defined(SWIFT_RUNTIME_FIXED_BACKTRACER_PATH)
 
     _swift_backtraceSetupEnvironment();
 
@@ -376,6 +393,7 @@ BacktraceInitializer::BacktraceInitializer() {
     if (_swift_backtraceSettings.algorithm == UnwindAlgorithm::Auto)
       _swift_backtraceSettings.algorithm = UnwindAlgorithm::Precise;
 
+#if !defined(SWIFT_RUNTIME_FIXED_BACKTRACER_PATH)
     size_t len = strlen(_swift_backtraceSettings.swiftBacktracePath);
     if (len > SWIFT_BACKTRACE_BUFFER_SIZE - 1) {
       swift::warning(0,
@@ -400,6 +418,7 @@ BacktraceInitializer::BacktraceInitializer() {
       }
 #endif // PROTECT_BACKTRACE_SETTINGS
     }
+#endif // !defined(SWIFT_RUNTIME_FIXED_BACKTRACER_PATH)
 
     _swift_backtraceSetupEnvironment();
 
@@ -632,6 +651,7 @@ _swift_processBacktracingSetting(llvm::StringRef key,
                      "swift runtime: unknown output-to setting '%.*s'\n",
                      static_cast<int>(value.size()), value.data());
     }
+#if !defined(SWIFT_RUNTIME_FIXED_BACKTRACER_PATH)
   } else if (key.equals_insensitive("swift-backtrace")) {
     size_t len = value.size();
     char *path = (char *)std::malloc(len + 1);
@@ -640,6 +660,7 @@ _swift_processBacktracingSetting(llvm::StringRef key,
 
     std::free(const_cast<char *>(_swift_backtraceSettings.swiftBacktracePath));
     _swift_backtraceSettings.swiftBacktracePath = path;
+#endif // !defined(SWIFT_RUNTIME_FIXED_BACKTRACER_PATH)
   } else {
     swift::warning(0,
                    "swift runtime: unknown backtracing setting '%.*s'\n",

stdlib/public/runtime/CMakeLists.txt

@@ -18,6 +18,11 @@ if(SWIFT_RUNTIME_ENABLE_LEAK_CHECKER)
   set(swift_runtime_leaks_sources Leaks.mm)
 endif()
 
+if(SWIFT_RUNTIME_FIXED_BACKTRACER_PATH)
+  list(APPEND swift_runtime_compile_flags
+    "-DSWIFT_RUNTIME_FIXED_BACKTRACER_PATH=\"${SWIFT_RUNTIME_FIXED_BACKTRACER_PATH}\"")
+endif()
+
 set(swift_runtime_objc_sources
     ErrorObject.mm
     SwiftObject.mm

utils/build-script-impl

@@ -236,6 +236,7 @@ KNOWN_SETTINGS=(
     swift-enable-experimental-string-processing   "1"               "whether to build experimental string processing feature"
     swift-earlyswiftsyntax                        "0"               "use the early SwiftSyntax"
     swift-enable-backtracing                      "1"               "whether to build the backtracing support"
+    swift-runtime-fixed-backtracer-path           ""                "if set, use a fixed path for the backtracer"
 
     ## FREESTANDING Stdlib Options
     swift-freestanding-flavor                     ""                "when building the FREESTANDING stdlib, which build style to use (options: apple, linux)"
@@ -1622,6 +1623,13 @@ for host in "${ALL_HOSTS[@]}"; do
         )
     fi
 
+    if [[ "${SWIFT_RUNTIME_FIXED_BACKTRACER_PATH}" ]] ; then
+        swift_cmake_options=(
+            "${swift_cmake_options[@]}"
+            -DSWIFT_RUNTIME_FIXED_BACKTRACER_PATH:STRING="${SWIFT_RUNTIME_FIXED_BACKTRACER_PATH}"
+        )
+    fi
+
     if [[ "${EXTRA_SWIFT_ARGS}" ]] ; then
         swift_cmake_options=(
             "${swift_cmake_options[@]}"
@@ -2050,6 +2058,13 @@ for host in "${ALL_HOSTS[@]}"; do
                     )
                 fi
 
+                if [[ "${SWIFT_RUNTIME_FIXED_BACKTRACER_PATH}" ]] ; then
+                    cmake_options=(
+                        "${cmake_options[@]}"
+                        -DSWIFT_RUNTIME_FIXED_BACKTRACER_PATH:STRING="${SWIFT_RUNTIME_FIXED_BACKTRACER_PATH}"
+                    )
+                fi
+
                 # SWIFT_THREADING_PACKAGE can be:
                 #
                 #    - Empty

utils/build_swift/build_swift/driver_arguments.py

@@ -455,6 +455,8 @@ def create_argument_parser():
     option('--swift-enable-backtracing', toggle_true,
            default=True,
            help='enable backtracing support')
+    option('--swift-runtime-fixed-backtracer-path', store,
+           help='if set, provide a fixed path for the Swift backtracer')
 
     option('--compiler-vendor', store,
            choices=['none', 'apple'],

utils/swift_build_support/swift_build_support/build_script_invocation.py

@@ -386,6 +386,12 @@ def convert_to_impl_arguments(self):
         if args.maccatalyst_ios_tests:
             impl_args += ["--darwin-test-maccatalyst-ios-like=1"]
 
+        # Provide a fixed backtracer path, if required
+        if args.swift_runtime_fixed_backtracer_path is not None:
+            impl_args += [
+                '--swift-runtime-fixed-backtracer-path=%s' % args.swift_runtime_fixed_backtracer_path
+            ]
+
         # If we have extra_cmake_options, combine all of them together and then
         # add them as one command.
         if args.extra_cmake_options: