add android support (#171)

* adjust for android

* update docs

* add const qualifier to `alloc_size`

* check const qualifier in cmake

CMakeLists.txt

@@ -2,6 +2,7 @@ cmake_minimum_required(VERSION 3.8)
 project(snmalloc C CXX)
 
 include(CheckCXXCompilerFlag)
+include(CheckCSourceCompiles)
 
 option(USE_SNMALLOC_STATS "Track allocation stats" OFF)
 option(SNMALLOC_CI_BUILD "Disable features not sensible for CI" OFF)
@@ -12,6 +13,12 @@ option(SNMALLOC_RUST_SUPPORT "Build static library for rust" OFF)
 option(SNMALLOC_QEMU_WORKAROUND "Disable using madvise(DONT_NEED) to zero memory on Linux" Off)
 set(CACHE_FRIENDLY_OFFSET OFF CACHE STRING "Base offset to place linked-list nodes.")
 
+CHECK_C_SOURCE_COMPILES("
+#include <malloc.h>
+size_t malloc_usable_size(const void* ptr) { return 0; }
+int main() { return 0; }
+" CONST_QUALIFIED_MALLOC_USABLE_SIZE)
+
 if ((CMAKE_BUILD_TYPE STREQUAL "Release") AND (NOT SNMALLOC_CI_BUILD))
   option(USE_POSIX_COMMIT_CHECKS "Instrument Posix PAL to check for access to unused blocks of memory." Off)
 else ()
@@ -135,6 +142,10 @@ if(USE_POSIX_COMMIT_CHECKS)
   target_compile_definitions(snmalloc_lib INTERFACE -DUSE_POSIX_COMMIT_CHECKS)
 endif()
 
+if(CONST_QUALIFIED_MALLOC_USABLE_SIZE)
+  target_compile_definitions(snmalloc_lib INTERFACE -DMALLOC_USABLE_SIZE_QUALIFIER=const)
+endif()
+
 
 # To build with just the header library target define SNMALLOC_ONLY_HEADER_LIBRARY
 # in containing Cmake file.

README.md

@@ -105,6 +105,16 @@ your toolchain:
 LD_PRELOAD=/usr/local/lib/libsnmallocshim.so ninja
 ```
 
+## Cross Compile for Android
+Android support is out-of-the-box.
+
+To cross-compile the library for arm android, you can simply invoke CMake with the toolchain file and the andorid api settings (for more infomation, check this [document](https://developer.android.com/ndk/guides/cmake)).
+
+For example, you can cross-compile for `arm64-v8a` with the following command:
+```
+cmake /path/to/snmalloc -DCMAKE_TOOLCHAIN_FILE=${ANDROID_NDK}/build/cmake/android.toolchain.cmake -DANDROID_ABI=arm64-v8a
+```
+
 # CMake Feature Flags
 
 These can be added to your cmake command line.

src/mem/alloc.h

@@ -457,7 +457,7 @@ namespace snmalloc
       return pointer_cast<void>(external_address<location>(p));
     }
 
-    static size_t alloc_size(void* p)
+    static size_t alloc_size(const void* p)
     {
       // This must be called on an external pointer.
       size_t size = ChunkMap::get(address_cast(p));

src/mem/mediumslab.h

@@ -39,9 +39,10 @@ namespace snmalloc
       return OS_PAGE_SIZE;
     }
 
-    static Mediumslab* get(void* p)
+    static Mediumslab* get(const void* p)
     {
-      return pointer_align_down<SUPERSLAB_SIZE, Mediumslab>(p);
+      return pointer_align_down<SUPERSLAB_SIZE, Mediumslab>(
+        const_cast<void*>(p));
     }
 
     void init(RemoteAllocator* alloc, sizeclass_t sc, size_t rsize)

src/mem/metaslab.h

@@ -140,9 +140,9 @@ namespace snmalloc
       return (slab_end - allocation_start) % size == 0;
     }
 
-    static Slab* get_slab(void* p)
+    static Slab* get_slab(const void* p)
     {
-      return pointer_align_down<SLAB_SIZE, Slab>(p);
+      return pointer_align_down<SLAB_SIZE, Slab>(const_cast<void*>(p));
     }
 
     static bool is_short(Slab* p)

src/mem/superslab.h

@@ -65,9 +65,10 @@ namespace snmalloc
       StatusChange = 2
     };
 
-    static Superslab* get(void* p)
+    static Superslab* get(const void* p)
     {
-      return pointer_align_down<SUPERSLAB_SIZE, Superslab>(p);
+      return pointer_align_down<SUPERSLAB_SIZE, Superslab>(
+        const_cast<void*>(p));
     }
 
     static bool is_short_sizeclass(sizeclass_t sizeclass)

src/override/malloc.cc

@@ -14,6 +14,10 @@ using namespace snmalloc;
 #  define SNMALLOC_NAME_MANGLE(a) a
 #endif
 
+#ifndef MALLOC_USABLE_SIZE_QUALIFIER
+#  define MALLOC_USABLE_SIZE_QUALIFIER
+#endif
+
 extern "C"
 {
   SNMALLOC_EXPORT void* SNMALLOC_NAME_MANGLE(__malloc_end_pointer)(void* ptr)
@@ -43,7 +47,9 @@ extern "C"
     return ThreadAlloc::get_noncachable()->alloc<ZeroMem::YesZero>(sz);
   }
 
-  SNMALLOC_EXPORT size_t SNMALLOC_NAME_MANGLE(malloc_usable_size)(void* ptr)
+  SNMALLOC_EXPORT
+  size_t SNMALLOC_NAME_MANGLE(malloc_usable_size)(
+    MALLOC_USABLE_SIZE_QUALIFIER void* ptr)
   {
     return Alloc::alloc_size(ptr);
   }

src/pal/pal_posix.h

@@ -2,8 +2,10 @@
 
 #include "../ds/address.h"
 #include "../mem/allocconfig.h"
-
-#include <execinfo.h>
+#if __has_include(<execinfo.h>)
+#  define SNMALLOC_HAS_BACKTRACE 1
+#  include <execinfo.h>
+#endif
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -40,6 +42,7 @@ namespace snmalloc
 
     static void print_stack_trace()
     {
+#ifdef SNMALLOC_HAS_BACKTRACE
       constexpr int SIZE = 1024;
       void* buffer[SIZE];
       auto nptrs = backtrace(buffer, SIZE);
@@ -47,6 +50,7 @@ namespace snmalloc
       backtrace_symbols_fd(buffer, nptrs, STDOUT_FILENO);
       puts("");
       fflush(stdout);
+#endif
     }
 
     /**