gh-99108: Disable HACL SIMD code on older versions of Android (#124304)

Disable HACL SIMD code on older versions of Android

Author: mhsmith

configure

@@ -7817,47 +7817,57 @@ case "$ac_sys_system" in
 esac
 AC_SUBST([LIBHACL_CFLAGS])
 
-dnl This can be extended here to detect e.g. Power8, which HACL* should also support.
-AX_CHECK_COMPILE_FLAG([-msse -msse2 -msse3 -msse4.1 -msse4.2],[
-  [LIBHACL_SIMD128_FLAGS="-msse -msse2 -msse3 -msse4.1 -msse4.2"]
-
-  AC_DEFINE([HACL_CAN_COMPILE_SIMD128], [1], [HACL* library can compile SIMD128 implementations])
-
-  # macOS universal2 builds *support* the -msse etc flags because they're
-  # available on x86_64. However, performance of the HACL SIMD128 implementation
-  # isn't great, so it's disabled on ARM64.
-  AC_MSG_CHECKING([for HACL* SIMD128 implementation])
-  if test "$UNIVERSAL_ARCHS" == "universal2"; then
-    [LIBHACL_SIMD128_OBJS="Modules/_hacl/Hacl_Hash_Blake2s_Simd128_universal2.o"]
-    AC_MSG_RESULT([universal2])
-  else
-    [LIBHACL_SIMD128_OBJS="Modules/_hacl/Hacl_Hash_Blake2s_Simd128.o"]
-    AC_MSG_RESULT([standard])
-  fi
-
-], [], [-Werror])
+# The SIMD files use aligned_alloc, which is not available on older versions of
+# Android.
+if test "$ac_sys_system" != "Linux-android" || test "$ANDROID_API_LEVEL" -ge 28; then
+  dnl This can be extended here to detect e.g. Power8, which HACL* should also support.
+  AX_CHECK_COMPILE_FLAG([-msse -msse2 -msse3 -msse4.1 -msse4.2],[
+    [LIBHACL_SIMD128_FLAGS="-msse -msse2 -msse3 -msse4.1 -msse4.2"]
+
+    AC_DEFINE([HACL_CAN_COMPILE_SIMD128], [1], [HACL* library can compile SIMD128 implementations])
+
+    # macOS universal2 builds *support* the -msse etc flags because they're
+    # available on x86_64. However, performance of the HACL SIMD128 implementation
+    # isn't great, so it's disabled on ARM64.
+    AC_MSG_CHECKING([for HACL* SIMD128 implementation])
+    if test "$UNIVERSAL_ARCHS" == "universal2"; then
+      [LIBHACL_SIMD128_OBJS="Modules/_hacl/Hacl_Hash_Blake2s_Simd128_universal2.o"]
+      AC_MSG_RESULT([universal2])
+    else
+      [LIBHACL_SIMD128_OBJS="Modules/_hacl/Hacl_Hash_Blake2s_Simd128.o"]
+      AC_MSG_RESULT([standard])
+    fi
 
+  ], [], [-Werror])
+fi
 AC_SUBST([LIBHACL_SIMD128_FLAGS])
 AC_SUBST([LIBHACL_SIMD128_OBJS])
 
-AX_CHECK_COMPILE_FLAG([-mavx2],[
-  [LIBHACL_SIMD256_FLAGS="-mavx2"]
-  AC_DEFINE([HACL_CAN_COMPILE_SIMD256], [1], [HACL* library can compile SIMD256 implementations])
-
-  # macOS universal2 builds *support* the -mavx2 compiler flag because it's
-  # available on x86_64; but the HACL SIMD256 build then fails because the
-  # implementation requires symbols that aren't available on ARM64. Use a
-  # wrapped implementation if we're building for universal2.
-  AC_MSG_CHECKING([for HACL* SIMD256 implementation])
-  if test "$UNIVERSAL_ARCHS" == "universal2"; then
-    [LIBHACL_SIMD256_OBJS="Modules/_hacl/Hacl_Hash_Blake2b_Simd256_universal2.o"]
-    AC_MSG_RESULT([universal2])
-  else
-    [LIBHACL_SIMD256_OBJS="Modules/_hacl/Hacl_Hash_Blake2b_Simd256.o"]
-    AC_MSG_RESULT([standard])
-  fi
-], [], [-Werror])
-
+# The SIMD files use aligned_alloc, which is not available on older versions of
+# Android.
+#
+# Although AVX support is not guaranteed on Android
+# (https://developer.android.com/ndk/guides/abis#86-64), this is safe because we do a
+# runtime CPUID check.
+if test "$ac_sys_system" != "Linux-android" || test "$ANDROID_API_LEVEL" -ge 28; then
+  AX_CHECK_COMPILE_FLAG([-mavx2],[
+    [LIBHACL_SIMD256_FLAGS="-mavx2"]
+    AC_DEFINE([HACL_CAN_COMPILE_SIMD256], [1], [HACL* library can compile SIMD256 implementations])
+
+    # macOS universal2 builds *support* the -mavx2 compiler flag because it's
+    # available on x86_64; but the HACL SIMD256 build then fails because the
+    # implementation requires symbols that aren't available on ARM64. Use a
+    # wrapped implementation if we're building for universal2.
+    AC_MSG_CHECKING([for HACL* SIMD256 implementation])
+    if test "$UNIVERSAL_ARCHS" == "universal2"; then
+      [LIBHACL_SIMD256_OBJS="Modules/_hacl/Hacl_Hash_Blake2b_Simd256_universal2.o"]
+      AC_MSG_RESULT([universal2])
+    else
+      [LIBHACL_SIMD256_OBJS="Modules/_hacl/Hacl_Hash_Blake2b_Simd256.o"]
+      AC_MSG_RESULT([standard])
+    fi
+  ], [], [-Werror])
+fi
 AC_SUBST([LIBHACL_SIMD256_FLAGS])
 AC_SUBST([LIBHACL_SIMD256_OBJS])