[Backtracing] Make the backtracer work for fully-static Linux.

The backtracer and its build system need a couple of changes to make
them work with the new fully-static Linux support.

rdar://123507656

stdlib/public/Backtracing/CMakeLists.txt

@@ -92,5 +92,5 @@ add_swift_target_library(swift_Backtracing ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} I
   INSTALL_IN_COMPONENT stdlib
   MACCATALYST_BUILD_FLAVOR "zippered"
 
-  TARGET_SDKS OSX LINUX
+  TARGET_SDKS OSX LINUX LINUX_STATIC
 )

stdlib/public/Backtracing/Context.swift

@@ -708,10 +708,10 @@ extension arm_gprs {
           }
         }
 
-	to[31] = mctx.sp
+	to[31] = UInt64(mctx.sp)
       }
     }
-    gprs.pc = mctx.pc
+    gprs.pc = UInt64(mctx.pc)
     gprs.valid = 0x1ffffffff
   }
 

stdlib/public/libexec/swift-backtrace/CMakeLists.txt

@@ -3,11 +3,13 @@
 set(darwin)
 set(wincrt_sdk)
 set(glibc)
+set(musl)
 
 if(SWIFT_BUILD_SDK_OVERLAY)
   set(darwin Darwin)
   set(wincrt_sdk CRT WinSDK)
   set(glibc Glibc)
+  set(musl Musl)
 endif()
 
 # Similarly, we only want the _Backtracing dependency if we're building
@@ -41,9 +43,10 @@ add_swift_target_executable(swift-backtrace BUILD_WITH_LIBEXEC
 
   SWIFT_MODULE_DEPENDS         ${backtracing}
 
-  SWIFT_MODULE_DEPENDS_OSX     ${darwin}
+  SWIFT_MODULE_DEPENDS_OSX          ${darwin}
-  SWIFT_MODULE_DEPENDS_WINDOWS ${wincrt_sdk}
+  SWIFT_MODULE_DEPENDS_WINDOWS      ${wincrt_sdk}
-  SWIFT_MODULE_DEPENDS_LINUX   ${glibc}
+  SWIFT_MODULE_DEPENDS_LINUX        ${glibc}
+  SWIFT_MODULE_DEPENDS_LINUX_STATIC ${musl}
 
   INSTALL_IN_COMPONENT libexec
   COMPILE_FLAGS
@@ -52,7 +55,14 @@ add_swift_target_executable(swift-backtrace BUILD_WITH_LIBEXEC
 
   TARGET_SDKS OSX LINUX)
 
+set(static_target_sdks)
 if(SWIFT_BUILD_STATIC_STDLIB)
+  list(APPEND static_target_sdks "LINUX")
+endif()
+if("LINUX_STATIC" IN_LIST SWIFT_SDKS)
+  list(APPEND static_target_sdks "LINUX_STATIC")
+endif()
+if(static_target_sdks)
   add_swift_target_executable(swift-backtrace-static BUILD_WITH_LIBEXEC
     PREFER_STATIC
 
@@ -60,14 +70,15 @@ if(SWIFT_BUILD_STATIC_STDLIB)
 
     SWIFT_MODULE_DEPENDS         ${backtracing}
 
-    SWIFT_MODULE_DEPENDS_OSX     ${darwin}
+    SWIFT_MODULE_DEPENDS_OSX          ${darwin}
-    SWIFT_MODULE_DEPENDS_WINDOWS ${wincrt_sdk}
+    SWIFT_MODULE_DEPENDS_WINDOWS      ${wincrt_sdk}
-    SWIFT_MODULE_DEPENDS_LINUX   ${glibc}
+    SWIFT_MODULE_DEPENDS_LINUX        ${glibc}
+    SWIFT_MODULE_DEPENDS_LINUX_STATIC ${musl}
 
     INSTALL_IN_COMPONENT libexec
     COMPILE_FLAGS
       ${BACKTRACING_COMPILE_FLAGS}
       -parse-as-library
 
-    TARGET_SDKS LINUX)
+    TARGET_SDKS ${static_target_sdks})
 endif()

stdlib/public/libexec/swift-backtrace/TargetLinux.swift

@@ -17,7 +17,11 @@
 
 #if os(Linux)
 
+#if canImport(Glibc)
 import Glibc
+#elseif canImport(Musl)
+import Musl
+#endif
 
 import _Backtracing
 @_spi(Internal) import _Backtracing

stdlib/public/libexec/swift-backtrace/Utils.swift

@@ -18,6 +18,8 @@
 import Darwin.C
 #elseif canImport(Glibc)
 import Glibc
+#elseif canImport(Musl)
+import Musl
 #elseif canImport(CRT)
 import CRT
 #endif

stdlib/public/libexec/swift-backtrace/main.swift

@@ -16,6 +16,8 @@
 import Darwin
 #elseif canImport(Glibc)
 import Glibc
+#elseif canImport(Musl)
+import Musl
 #elseif canImport(CRT)
 import CRT
 #endif

stdlib/public/runtime/CrashHandlerLinux.cpp

@@ -16,6 +16,14 @@
 
 #ifdef __linux__
 
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE 1
+#endif
+
+#ifndef _LARGEFILE64_SOURCE
+#define _LARGEFILE64_SOURCE 1
+#endif
+
 #include <linux/capability.h>
 #include <linux/futex.h>
 

stdlib/public/runtime/Paths.cpp

@@ -525,6 +525,18 @@ _swift_initRuntimePath(void *) {
   int ret = ::dladdr((void *)_swift_initRuntimePath, &dli);
 
   if (!ret) {
+#ifdef __linux__
+    // If we don't find anything, try reading /proc/self/exe as a fallback;
+    // this is needed with Musl when statically linking because in that case
+    // dladdr() does nothing.
+    char pathBuf[4096];
+    ssize_t len = readlink("/proc/self/exe", pathBuf, sizeof(pathBuf));
+    if (len > 0 && len < sizeof(pathBuf)) {
+      runtimePath = ::strdup(pathBuf);
+      return;
+    }
+#endif
+
     swift::fatalError(/* flags = */ 0,
                       "Unable to obtain Swift runtime path\n");
   }