PoC: Support of older Android versions (aiming SDK 23 / this version works for SDK 24+ though)

Author: birdofpreyru

CMakeLists.txt

@@ -100,6 +100,29 @@ if(CMAKE_SYSTEM_NAME MATCHES "Android")
   )
 endif()
 
+# Builds & places for packing the glob library, for Android-targeted builds.
+if(CMAKE_SYSTEM_NAME MATCHES "Android")
+  execute_process(
+    COMMAND ${CMAKE_COMMAND} ${CMAKE_CURRENT_SOURCE_DIR}/glob
+      -B ${CMAKE_BINARY_DIR}/glob
+      -DCMAKE_BUILD_TYPE=Release
+      -DCMAKE_INSTALL_PREFIX=${CMAKE_BINARY_DIR}/sysroot
+      -DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}
+      ${EXTRA_BUILD_ARGS}
+    COMMAND_ECHO STDOUT
+    COMMAND_ERROR_IS_FATAL ANY
+  )
+  execute_process(
+    COMMAND ${CMAKE_COMMAND} --build ${CMAKE_BINARY_DIR}/glob
+      --config Release ${EXTRA_INSTALL_ARGS}
+  )
+  execute_process(COMMAND ${CMAKE_COMMAND} --install ${CMAKE_BINARY_DIR}/glob)
+  file(
+    COPY ${CMAKE_BINARY_DIR}/sysroot/lib/libglob.so
+    DESTINATION ${CMAKE_CURRENT_SOURCE_DIR}/android/src/main/jniLibs/${ANDROID_ABI}
+  )
+endif()
+
 if(CMAKE_SYSTEM_NAME MATCHES "Android|Windows")
   set(BUILD_SHARED_LIBS 1)
 endif()

example/android/build.gradle

@@ -1,7 +1,7 @@
 buildscript {
     ext {
         buildToolsVersion = "34.0.0"
-        minSdkVersion = 28
+        minSdkVersion = 23
         compileSdkVersion = 34
         targetSdkVersion = 34
         ndkVersion = "26.1.10909125"

glob/CMakeLists.txt

@@ -0,0 +1,14 @@
+cmake_minimum_required(VERSION 3.5 FATAL_ERROR)
+project(GLOB C)
+
+set(CMAKE_C_STANDARD 99)
+set(CMAKE_C_STANDARD_REQUIRED TRUE)
+
+set(HEADERS collate.h freebsd-compat.h glob.h)
+set(SOURCES glob.c)
+
+add_compile_definitions(__USE_BSD)
+add_library(glob ${HEADERS} ${SOURCES})
+
+install(TARGETS glob)
+install(FILES ${HEADERS} DESTINATION include)

glob/README.md

@@ -0,0 +1,5 @@
+The Glob library is a part of Android SDK starting from SDK 28; thus, to support
+older SDKs we compile it from sources. These source files are taken from
+the https://android.googlesource.com/platform/bionic repository
+([bionic](https://en.wikipedia.org/wiki/Bionic_%28software%29)
+is Android's C library, math library, and dynamic linker).

glob/collate.h

@@ -0,0 +1,26 @@
+#include "freebsd-compat.h"
+
+/**
+ * [reallocarray(3)](https://man7.org/linux/man-pages/man3/realloc.3.html) resizes
+ * allocated memory on the heap.
+ *
+ * Equivalent to `realloc(__ptr, __item_count * __item_size)` but fails if the
+ * multiplication overflows.
+ *
+ * Returns a pointer (which may be different from `__ptr`) to the resized
+ * memory on success and returns a null pointer and sets `errno` on failure
+ * (but see the notes for malloc()).
+ */
+#if __ANDROID_API__ >= 29
+void* _Nullable reallocarray(void* _Nullable __ptr, size_t __item_count, size_t __item_size) __BIONIC_ALLOC_SIZE(2, 3) __INTRODUCED_IN(29);
+#else
+#include <errno.h>
+static __inline void* _Nullable reallocarray(void* _Nullable __ptr, size_t __item_count, size_t __item_size) {
+  size_t __new_size;
+  if (__builtin_mul_overflow(__item_count, __item_size, &__new_size)) {
+    errno = ENOMEM;
+    return NULL;
+  }
+  return realloc(__ptr, __new_size);
+}
+#endif

glob/freebsd-compat.h

@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#pragma once
+
+#define _BSD_SOURCE
+
+#define REPLACE_GETOPT
+
+/* FreeBSD has this, but we can't really implement it correctly on Linux. */
+#define issetugid() 0
+
+#define __compiler_membar() __asm __volatile(" " : : : "memory")