[compiler-rt] [Fuzzer] Enable custom libc++ for Android (PR #70407)

[Ryan Prichard via llvm-commits]

https://github.com/rprichard created https://github.com/llvm/llvm-project/pull/70407

The Android LLVM build system builds the arm64 fuzzer lib without HWASan, but then applications that enable HWASan can generated an object file with a HWASan-ified version of some libc++ symbols (e.g. `std::__1::piecewise_construct`). The linker can choose the HWASan-ified definition, but then it cannot resolve the relocation from libclang_rt.fuzzer-aarch64-android.a to this symbol because the high bits of the address are unexpectedly set. This produces an error:

```
relocation R_AARCH64_ADR_PREL_PG_HI21 out of range
```

Fix this problem by linking a custom isolated libc++ into Android's fuzzer library.

We need to pass through ANDROID_NATIVE_API_LEVEL so that the libc++ for 32-bit Android (API < 24) uses LLVM_FORCE_SMALLFILE_FOR_ANDROID.

>From f45572a84d32fec2a20cfba15a19040e2ca02da0 Mon Sep 17 00:00:00 2001
From: Ryan Prichard <rprichard at google.com>
Date: Thu, 26 Oct 2023 19:29:49 -0700
Subject: [PATCH] [Fuzzer] Enable custom libc++ for Android

The Android LLVM build system builds the arm64 fuzzer lib without
HWASan, but then applications that enable HWASan can generated an
object file with a HWASan-ified version of some libc++ symbols (e.g.
`std::__1::piecewise_construct`). The linker can choose the
HWASan-ified definition, but then it cannot resolve the relocation from
libclang_rt.fuzzer-aarch64-android.a to this symbol because the high
bits of the address are unexpectedly set. This produces an error:

```
relocation R_AARCH64_ADR_PREL_PG_HI21 out of range
```

Fix this problem by linking a custom isolated libc++ into Android's
fuzzer library.

We need to pass through ANDROID_NATIVE_API_LEVEL so that the libc++
for 32-bit Android (API < 24) uses LLVM_FORCE_SMALLFILE_FOR_ANDROID.
---
 compiler-rt/cmake/Modules/AddCompilerRT.cmake | 2 ++
 compiler-rt/lib/fuzzer/CMakeLists.txt         | 4 ++--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/compiler-rt/cmake/Modules/AddCompilerRT.cmake b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
index 5ed49f0f5588144..9c9d256a58b61be 100644
--- a/compiler-rt/cmake/Modules/AddCompilerRT.cmake
+++ b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
@@ -625,6 +625,8 @@ macro(add_custom_libcxx name prefix)
   set_target_properties(${name}-clobber PROPERTIES FOLDER "Compiler-RT Misc")
 
   set(PASSTHROUGH_VARIABLES
+    ANDROID
+    ANDROID_NATIVE_API_LEVEL
     CMAKE_C_COMPILER_TARGET
     CMAKE_CXX_COMPILER_TARGET
     CMAKE_SHARED_LINKER_FLAGS
diff --git a/compiler-rt/lib/fuzzer/CMakeLists.txt b/compiler-rt/lib/fuzzer/CMakeLists.txt
index a9a10f724d1aa35..fb5adf1e5c9e698 100644
--- a/compiler-rt/lib/fuzzer/CMakeLists.txt
+++ b/compiler-rt/lib/fuzzer/CMakeLists.txt
@@ -59,7 +59,7 @@ CHECK_CXX_SOURCE_COMPILES("
 
 set(LIBFUZZER_CFLAGS ${COMPILER_RT_COMMON_CFLAGS})
 
-if(OS_NAME MATCHES "Linux|Fuchsia" AND
+if(OS_NAME MATCHES "Android|Linux|Fuchsia" AND
    COMPILER_RT_LIBCXX_PATH AND
    COMPILER_RT_LIBCXXABI_PATH)
   list(APPEND LIBFUZZER_CFLAGS -D_LIBCPP_ABI_VERSION=Fuzzer)
@@ -135,7 +135,7 @@ add_compiler_rt_runtime(clang_rt.fuzzer_interceptors
   CFLAGS ${LIBFUZZER_CFLAGS}
   PARENT_TARGET fuzzer)
 
-if(OS_NAME MATCHES "Linux|Fuchsia" AND
+if(OS_NAME MATCHES "Android|Linux|Fuchsia" AND
    COMPILER_RT_LIBCXX_PATH AND
    COMPILER_RT_LIBCXXABI_PATH)
   macro(partially_link_libcxx name dir arch)