[AArch64][compiler-rt] Option to build compiler-rt without FMV support.

[ilinpv]

Summary

This commit adds compiler-rt cmake option COMPILER_RT_DISABLE_AARCH64_FMV
which, when enabled, doesn't include function multiversioning features
initilization code in 'builtins' build.

[smeenai]

LGTM, thank you!

[abrachet]

compiler-rt/lib/builtins/cpu_model.c

869–870

This was moved after the #ifndef checks for the various defines like AT_HWCAP and HWCAP_ATOMICS which causes the build to fail if these are not defined. I've created D141285 to fix this

Example failure:

[195/255](34) Building C object CMakeFiles/clang_rt.builtins-aarch64.dir/cpu_model.c.o
FAILED: CMakeFiles/clang_rt.builtins-aarch64.dir/cpu_model.c.o 
/b/s/w/ir/cache/goma/client/gomacc /b/s/w/ir/x/w/staging/llvm_build/./bin/clang --target=aarch64-unknown-linux-gnu --sysroot=/b/s/w/ir/x/w/cipd/linux -DHAS_ASM_LSE -DVISIBILITY_HIDDEN  -O3 -DNDEBUG -DCOMPILER_RT_HAS_FLOAT16 -std=c11 -fPIC -fno-builtin -fvisibility=hidden -fomit-frame-pointer -MD -MT CMakeFiles/clang_rt.builtins-aarch64.dir/cpu_model.c.o -MF CMakeFiles/clang_rt.builtins-aarch64.dir/cpu_model.c.o.d -o CMakeFiles/clang_rt.builtins-aarch64.dir/cpu_model.c.o -c /b/s/w/ir/x/w/llvm-llvm-project/compiler-rt/lib/builtins/cpu_model.c
/b/s/w/ir/x/w/llvm-llvm-project/compiler-rt/lib/builtins/cpu_model.c:881:27: error: use of undeclared identifier 'HWCAP_ATOMICS'
  _Bool result = (hwcap & HWCAP_ATOMICS) != 0;
                          ^
1 error generated.

compiler-rt/CMakeLists.txt

 
 include(SetPlatformToolchainTools)
 include(base-config-ix)
 include(CompilerRTUtils)
 include(CMakeDependentOption)
 
 option(COMPILER_RT_BUILD_BUILTINS "Build builtins" ON)
 mark_as_advanced(COMPILER_RT_BUILD_BUILTINS)
+option(COMPILER_RT_DISABLE_AARCH64_FMV "Disable AArch64 Function Multi Versioning support" OFF)
+mark_as_advanced(COMPILER_RT_DISABLE_AARCH64_FMV)
 option(COMPILER_RT_BUILD_CRT "Build crtbegin.o/crtend.o" ON)
 mark_as_advanced(COMPILER_RT_BUILD_CRT)
 option(COMPILER_RT_CRT_USE_EH_FRAME_REGISTRY "Use eh_frame in crtbegin.o/crtend.o" ON)
 mark_as_advanced(COMPILER_RT_CRT_USE_EH_FRAME_REGISTRY)
 option(COMPILER_RT_BUILD_SANITIZERS "Build sanitizers" ON)
 mark_as_advanced(COMPILER_RT_BUILD_SANITIZERS)
 option(COMPILER_RT_BUILD_XRAY "Build xray" ON)
 mark_as_advanced(COMPILER_RT_BUILD_XRAY)

compiler-rt/lib/builtins/CMakeLists.txt

else ()
   endif()
 
   set(BUILTIN_DEFS "")
 
   if(COMPILER_RT_BUILTINS_HIDE_SYMBOLS)
     append_list_if(COMPILER_RT_HAS_VISIBILITY_HIDDEN_FLAG VISIBILITY_HIDDEN BUILTIN_DEFS)
   endif()
 
+  if(COMPILER_RT_DISABLE_AARCH64_FMV)
+    list(APPEND BUILTIN_DEFS DISABLE_AARCH64_FMV)
+  endif()
+
   append_list_if(COMPILER_RT_HAS_ASM_LSE HAS_ASM_LSE BUILTIN_DEFS)
 
   foreach (arch ${BUILTIN_SUPPORTED_ARCH})
     if (CAN_TARGET_${arch})
       set(BUILTIN_CFLAGS_${arch} ${BUILTIN_CFLAGS})
       # For ARM archs, exclude any VFP builtins if VFP is not supported
       if (${arch} MATCHES "^(arm|armhf|armv7|armv7s|armv7k|armv7m|armv7em|armv8m.main|armv8.1m.main)$")
         string(REPLACE ";" " " _TARGET_${arch}_CFLAGS "${TARGET_${arch}_CFLAGS}")

compiler-rt/lib/builtins/cpu_model.c

int CONSTRUCTOR_ATTRIBUTE __cpu_indicator_init(void) {
 
   assert(__cpu_model.__cpu_vendor < VENDOR_MAX);
   assert(__cpu_model.__cpu_type < CPU_TYPE_MAX);
   assert(__cpu_model.__cpu_subtype < CPU_SUBTYPE_MAX);
 
   return 0;
 }
 #elif defined(__aarch64__)
+// LSE support detection for out-of-line atomics
+// using HWCAP and Auxiliary vector
+_Bool __aarch64_have_lse_atomics
+    __attribute__((visibility("hidden"), nocommon));
+
+#if defined(__has_include)
+#if __has_include(<sys/auxv.h>)
+#include <sys/auxv.h>
+#if __has_include(<asm/hwcap.h>)
+#include <asm/hwcap.h>
+
+#if defined(__ANDROID__)
+#include <string.h>
+#include <sys/system_properties.h>
+#elif defined(__Fuchsia__)
+#include <zircon/features.h>
+#include <zircon/syscalls.h>
+#endif
+
+// Detect Exynos 9810 CPU
+#define IF_EXYNOS9810                                                          \
+  char arch[PROP_VALUE_MAX];                                                   \
+  if (__system_property_get("ro.arch", arch) > 0 &&                            \
+      strncmp(arch, "exynos9810", sizeof("exynos9810") - 1) == 0)
+
+static void CONSTRUCTOR_ATTRIBUTE init_have_lse_atomics(void) {
+#if defined(__FreeBSD__)
+  unsigned long hwcap;
+  int result = elf_aux_info(AT_HWCAP, &hwcap, sizeof hwcap);
+  __aarch64_have_lse_atomics = result == 0 && (hwcap & HWCAP_ATOMICS) != 0;
+#elif defined(__Fuchsia__)
+  // This ensures the vDSO is a direct link-time dependency of anything that
+  // needs this initializer code.
+#pragma comment(lib, "zircon")
+  uint32_t features;
+  zx_status_t status = _zx_system_get_features(ZX_FEATURE_KIND_CPU, &features);
+  __aarch64_have_lse_atomics =
+      status == ZX_OK && (features & ZX_ARM64_FEATURE_ISA_ATOMICS) != 0;
+#else
+  unsigned long hwcap = getauxval(AT_HWCAP);
+  _Bool result = (hwcap & HWCAP_ATOMICS) != 0;
+#if defined(__ANDROID__)
+  if (result) {
+    // Some cores in the Exynos 9810 CPU are ARMv8.2 and others are ARMv8.0;
+    // only the former support LSE atomics.  However, the kernel in the
+    // initial Android 8.0 release of Galaxy S9/S9+ devices incorrectly
+    // reported the feature as being supported.
+    //
+    // The kernel appears to have been corrected to mark it unsupported as of
+    // the Android 9.0 release on those devices, and this issue has not been
+    // observed anywhere else. Thus, this workaround may be removed if
+    // compiler-rt ever drops support for Android 8.0.
+    IF_EXYNOS9810 result = false;
+  }
+#endif // defined(__ANDROID__)
+  __aarch64_have_lse_atomics = result;
+#endif // defined(__FreeBSD__)
+}
+
+#if !defined(DISABLE_AARCH64_FMV)
 // CPUFeatures must correspond to the same AArch64 features in
 // AArch64TargetParser.h
 enum CPUFeatures {
   FEAT_RNG,
   FEAT_FLAGM,
   FEAT_FLAGM2,
   FEAT_FP16FML,
   FEAT_DOTPROD,
enum CPUFeatures {
   FEAT_LS64_V,
   FEAT_LS64_ACCDATA,
   FEAT_WFXT,
   FEAT_SME_F64,
   FEAT_SME_I64,
   FEAT_SME2,
   FEAT_MAX
 };
+
 // Architecture features used
 // in Function Multi Versioning
 struct {
   unsigned long long features;
   // As features grows new fields could be added
 } __aarch64_cpu_features __attribute__((visibility("hidden"), nocommon));
 
-// LSE support detection for out-of-line atomics
-// using HWCAP and Auxiliary vector
-_Bool __aarch64_have_lse_atomics
-    __attribute__((visibility("hidden"), nocommon));
-#if defined(__has_include)
-#if __has_include(<sys/auxv.h>)
-#include <sys/auxv.h>
-#if __has_include(<asm/hwcap.h>)
-#include <asm/hwcap.h>
-
 #ifndef AT_HWCAP
 #define AT_HWCAP 16
 #endif
-
 #ifndef HWCAP_CPUID
 #define HWCAP_CPUID (1 << 11)
 #endif
 #ifndef HWCAP_FP
 #define HWCAP_FP (1 << 0)
 #endif
 #ifndef HWCAP_ASIMD
 #define HWCAP_ASIMD (1 << 1)

 #endif
 #ifndef HWCAP2_EBF16
 #define HWCAP2_EBF16 (1UL << 32)
 #endif
 #ifndef HWCAP2_SVE_EBF16
 #define HWCAP2_SVE_EBF16 (1UL << 33)
 #endif
 
-#if defined(__ANDROID__)
-#include <string.h>
-#include <sys/system_properties.h>
-#elif defined(__Fuchsia__)
-#include <zircon/features.h>
-#include <zircon/syscalls.h>
-#endif
-
-// Detect Exynos 9810 CPU
-#define IF_EXYNOS9810                                                          \
-  char arch[PROP_VALUE_MAX];                                                   \
-  if (__system_property_get("ro.arch", arch) > 0 &&                            \
-      strncmp(arch, "exynos9810", sizeof("exynos9810") - 1) == 0)
-
-static void CONSTRUCTOR_ATTRIBUTE init_have_lse_atomics(void) {
-#if defined(__FreeBSD__)
-  unsigned long hwcap;
-  int result = elf_aux_info(AT_HWCAP, &hwcap, sizeof hwcap);
-  __aarch64_have_lse_atomics = result == 0 && (hwcap & HWCAP_ATOMICS) != 0;
-#elif defined(__Fuchsia__)
-  // This ensures the vDSO is a direct link-time dependency of anything that
-  // needs this initializer code.
-#pragma comment(lib, "zircon")
-  uint32_t features;
-  zx_status_t status = _zx_system_get_features(ZX_FEATURE_KIND_CPU, &features);
-  __aarch64_have_lse_atomics =
-      status == ZX_OK && (features & ZX_ARM64_FEATURE_ISA_ATOMICS) != 0;
-#else
-  unsigned long hwcap = getauxval(AT_HWCAP);
-  _Bool result = (hwcap & HWCAP_ATOMICS) != 0;
-#if defined(__ANDROID__)
-  if (result) {
-    // Some cores in the Exynos 9810 CPU are ARMv8.2 and others are ARMv8.0;
-    // only the former support LSE atomics.  However, the kernel in the
-    // initial Android 8.0 release of Galaxy S9/S9+ devices incorrectly
-    // reported the feature as being supported.
-    //
-    // The kernel appears to have been corrected to mark it unsupported as of
-    // the Android 9.0 release on those devices, and this issue has not been
-    // observed anywhere else. Thus, this workaround may be removed if
-    // compiler-rt ever drops support for Android 8.0.
-    IF_EXYNOS9810 result = false;
-  }
-#endif // defined(__ANDROID__)
-  __aarch64_have_lse_atomics = result;
-#endif // defined(__FreeBSD__)
-}
-
 void init_cpu_features_resolver(unsigned long hwcap, unsigned long hwcap2) {
 #define setCPUFeature(F) __aarch64_cpu_features.features |= 1ULL << F
 #define getCPUFeature(id, ftr) __asm__("mrs %0, " #id : "=r"(ftr))
 #define extractBits(val, start, number)                                        \
   (val & ((1ULL << number) - 1ULL) << start) >> start
   if (hwcap & HWCAP_CRC32)
     setCPUFeature(FEAT_CRC);
   if (hwcap & HWCAP_PMULL)
#endif // defined(__ANDROID__)
   hwcap2 = getauxval(AT_HWCAP2);
 #endif // defined(__FreeBSD__)
   init_cpu_features_resolver(hwcap, hwcap2);
 #undef extractBits
 #undef getCPUFeature
 #undef setCPUFeature
 #undef IF_EXYNOS9810
 }
+#endif // !defined(DISABLE_AARCH64_FMV)
 #endif // defined(__has_include)
 #endif // __has_include(<sys/auxv.h>)
 #endif // __has_include(<asm/hwcap.h>)
 #endif // defined(__aarch64__)