[compiler-rt] Add CMake option to enable execute-only code generation on AArch64 (llvm#140555)

For a full toolchain supporting execute-only code generation the runtime
libraries also need to be pre-compiled with it enabled. The generic
`RUNTIMES_EXECUTE_ONLY_CODE` CMake option can now be used during build
configuration to enable execute-only code generation in compiler-rt.

The build option can only be enabled for a runtimes build of
compiler-rt, because a recent version of Clang is needed to correctly
compile assembly files with execute-only code support.

Related RFC:
https://discourse.llvm.org/t/rfc-execute-only-code-support-for-runtime-libraries-on-aarch64/86180

Author: Il-Capitano

compiler-rt/CMakeLists.txt

@@ -605,6 +605,10 @@ string(REGEX REPLACE "-stdlib=[a-zA-Z+]*" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}
 list(APPEND COMPILER_RT_COMMON_CFLAGS ${stdlib_flag})
 list(APPEND COMPILER_RT_COMMON_LINK_FLAGS ${stdlib_flag})
 
+# Add assembler flags for execute-only code generation. C and C++ flags should have already
+# been added to CMAKE_C_FLAGS and CMAKE_CXX_FLAGS.
+append_string_if(RUNTIMES_EXECUTE_ONLY_CODE -DCOMPILER_RT_EXECUTE_ONLY_CODE CMAKE_ASM_FLAGS)
+
 # TODO: There's a lot of duplication across lib/*/tests/CMakeLists.txt files,
 # move some of the common flags to COMPILER_RT_UNITTEST_CFLAGS.
 

compiler-rt/lib/builtins/assembly.h

@@ -71,9 +71,24 @@
 
 #endif
 
+#if defined(__aarch64__) && defined(__ELF__) &&                                \
+    defined(COMPILER_RT_EXECUTE_ONLY_CODE)
+// The assembler always creates an implicit '.text' section with default flags
+// (SHF_ALLOC | SHF_EXECINSTR), which is incompatible with the execute-only
+// '.text' section we want to create here because of the missing
+// SHF_AARCH64_PURECODE section flag. To solve this, we use 'unique,0' to
+// differentiate the two sections. The output will therefore have two separate
+// sections named '.text', where code will be placed into the execute-only
+// '.text' section, and the implicitly-created one will be empty.
+#define TEXT_SECTION                                                           \
+  .section .text,"axy",@progbits,unique,0
+#else
+#define TEXT_SECTION                                                           \
+  .text
+#endif
+
 #if defined(__arm__) || defined(__aarch64__) || defined(__arm64ec__)
 #define FUNC_ALIGN                                                             \
-  .text SEPARATOR                                                              \
   .balign 16 SEPARATOR
 #else
 #define FUNC_ALIGN
@@ -255,6 +270,7 @@
 #endif
 
 #define DEFINE_COMPILERRT_FUNCTION(name)                                       \
+  TEXT_SECTION SEPARATOR                                                       \
   DEFINE_CODE_STATE                                                            \
   FILE_LEVEL_DIRECTIVE SEPARATOR                                               \
   .globl FUNC_SYMBOL(SYMBOL_NAME(name)) SEPARATOR                              \
@@ -264,6 +280,7 @@
   FUNC_SYMBOL(SYMBOL_NAME(name)):
 
 #define DEFINE_COMPILERRT_THUMB_FUNCTION(name)                                 \
+  TEXT_SECTION SEPARATOR                                                       \
   DEFINE_CODE_STATE                                                            \
   FILE_LEVEL_DIRECTIVE SEPARATOR                                               \
   .globl FUNC_SYMBOL(SYMBOL_NAME(name)) SEPARATOR                              \
@@ -273,6 +290,7 @@
   FUNC_SYMBOL(SYMBOL_NAME(name)):
 
 #define DEFINE_COMPILERRT_PRIVATE_FUNCTION(name)                               \
+  TEXT_SECTION SEPARATOR                                                       \
   DEFINE_CODE_STATE                                                            \
   FILE_LEVEL_DIRECTIVE SEPARATOR                                               \
   .globl FUNC_SYMBOL(SYMBOL_NAME(name)) SEPARATOR                              \
@@ -282,6 +300,7 @@
   FUNC_SYMBOL(SYMBOL_NAME(name)):
 
 #define DEFINE_COMPILERRT_PRIVATE_FUNCTION_UNMANGLED(name)                     \
+  TEXT_SECTION SEPARATOR                                                       \
   DEFINE_CODE_STATE                                                            \
   .globl FUNC_SYMBOL(name) SEPARATOR                                           \
   SYMBOL_IS_FUNC(name) SEPARATOR                                               \
@@ -290,6 +309,7 @@
   FUNC_SYMBOL(name):
 
 #define DEFINE_COMPILERRT_OUTLINE_FUNCTION_UNMANGLED(name)                     \
+  TEXT_SECTION SEPARATOR                                                       \
   DEFINE_CODE_STATE                                                            \
   FUNC_ALIGN                                                                   \
   .globl FUNC_SYMBOL(name) SEPARATOR                                           \

compiler-rt/lib/fuzzer/CMakeLists.txt

@@ -162,6 +162,7 @@ if(OS_NAME MATCHES "Android|Linux|Fuchsia" AND
       CFLAGS ${TARGET_CFLAGS}
       CMAKE_ARGS -DCMAKE_CXX_COMPILER_WORKS=ON
                  -DCMAKE_POSITION_INDEPENDENT_CODE=ON
+                 -DRUNTIMES_EXECUTE_ONLY_CODE=${RUNTIMES_EXECUTE_ONLY_CODE}
                  -DLIBCXXABI_ENABLE_EXCEPTIONS=OFF
                  -DLIBCXX_ABI_NAMESPACE=__Fuzzer
                  -DLIBCXX_ENABLE_EXCEPTIONS=OFF)

compiler-rt/lib/hwasan/hwasan_setjmp_aarch64.S

@@ -28,7 +28,7 @@
 // stack pointer when compiling a C function.
 // Hence we have to write this function in assembly.
 
-.section .text
+TEXT_SECTION
 .file "hwasan_setjmp_aarch64.S"
 
 .global ASM_WRAPPER_NAME(setjmp)

compiler-rt/lib/hwasan/hwasan_tag_mismatch_aarch64.S

@@ -70,7 +70,7 @@
 // clobbering the x17 register in error reports, and that the program will have
 // a runtime dependency on the __hwasan_tag_mismatch_v2 symbol therefore it will
 // fail to start up given an older (i.e. incompatible) runtime.
-.section .text
+TEXT_SECTION
 .file "hwasan_tag_mismatch_aarch64.S"
 .global __hwasan_tag_mismatch
 .type __hwasan_tag_mismatch, %function

compiler-rt/lib/msan/tests/CMakeLists.txt

@@ -139,6 +139,7 @@ if(COMPILER_RT_CAN_EXECUTE_TESTS AND
     add_custom_libcxx(libcxx_msan_${arch} ${LIBCXX_PREFIX}
       DEPS ${MSAN_RUNTIME_LIBRARIES}
       CFLAGS ${MSAN_LIBCXX_CFLAGS} ${TARGET_CFLAGS}
+      CMAKE_ARGS -DRUNTIMES_EXECUTE_ONLY_CODE=${RUNTIMES_EXECUTE_ONLY_CODE}
       USE_TOOLCHAIN)
     set(MSAN_LIBCXX_DIR ${LIBCXX_PREFIX}/lib/)
 

compiler-rt/lib/orc/elfnix_tls.aarch64.S

@@ -13,9 +13,11 @@
 // The content of this file is aarch64-only
 #if defined(__arm64__) || defined(__aarch64__)
 
+#include "builtins/assembly.h"
+
 #define REGISTER_SAVE_SPACE_SIZE     32 * 24
 
-        .text
+        TEXT_SECTION
 
   // returns address of TLV in x0, all other registers preserved
   // TODO: add fast-path for repeat access

compiler-rt/lib/orc/sysv_reenter.arm64.S

@@ -13,7 +13,9 @@
 // The content of this file is arm64-only
 #if defined(__arm64__) || defined(__aarch64__)
 
-        .text
+#include "builtins/assembly.h"
+
+        TEXT_SECTION
 
         // Saves GPRs, calls __orc_rt_resolve
         .globl __orc_rt_sysv_reenter

compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors_vfork_aarch64.inc.S

@@ -5,6 +5,7 @@
 
 ASM_HIDDEN(COMMON_INTERCEPTOR_SPILL_AREA)
 
+TEXT_SECTION
 .comm _ZN14__interception10real_vforkE,8,8
 .globl ASM_WRAPPER_NAME(vfork)
 ASM_TYPE_FUNCTION(ASM_WRAPPER_NAME(vfork))

compiler-rt/lib/tsan/CMakeLists.txt

@@ -30,6 +30,7 @@ if(COMPILER_RT_LIBCXX_PATH AND
     add_custom_libcxx(libcxx_tsan_${arch} ${LIBCXX_PREFIX}
       DEPS ${TSAN_RUNTIME_LIBRARIES}
       CFLAGS ${TARGET_CFLAGS} -fsanitize=thread
+      CMAKE_ARGS -DRUNTIMES_EXECUTE_ONLY_CODE=${RUNTIMES_EXECUTE_ONLY_CODE}
       USE_TOOLCHAIN)
     list(APPEND libcxx_tsan_deps libcxx_tsan_${arch}-install-cmake326-workaround)
   endforeach()