Make CRYPTO_is_NEON_capable aware of the buggy CPU.

If we're to allow the buggy CPU workaround to fire when __ARM_NEON__ is set,
CRYPTO_is_NEON_capable also needs to be aware of it. Also add an API to export
this value out of BoringSSL, so we can get some metrics on how prevalent this
chip is.

BUG=chromium:606629

Change-Id: I97d65a47a6130689098b32ce45a8c57c468aa405
Reviewed-on: https://boringssl-review.googlesource.com/7796
Reviewed-by: Adam Langley <agl@google.com>

crypto/cpu-arm-linux.c

@@ -288,6 +288,8 @@ static int has_broken_neon(const STRING_PIECE *cpuinfo) {
 
 extern uint32_t OPENSSL_armcap_P;
 
+static int g_has_broken_neon;
+
 void OPENSSL_cpuid_setup(void) {
   char *cpuinfo_data;
   size_t cpuinfo_len;
@@ -317,7 +319,8 @@ void OPENSSL_cpuid_setup(void) {
   }
 
   /* Clear NEON support if known broken. */
-  if (has_broken_neon(&cpuinfo)) {
+  g_has_broken_neon = has_broken_neon(&cpuinfo);
+  if (g_has_broken_neon) {
     hwcap &= ~HWCAP_NEON;
   }
 
@@ -352,4 +355,6 @@ void OPENSSL_cpuid_setup(void) {
   OPENSSL_free(cpuinfo_data);
 }
 
+int CRYPTO_has_broken_NEON(void) { return g_has_broken_neon; }
+
 #endif /* OPENSSL_ARM && !OPENSSL_STATIC_ARMCAP */

include/openssl/cpu.h

@@ -110,13 +110,24 @@ OPENSSL_EXPORT char CRYPTO_is_NEON_capable_at_runtime(void);
 /* CRYPTO_is_NEON_capable returns true if the current CPU has a NEON unit. If
  * this is known statically then it returns one immediately. */
 static inline int CRYPTO_is_NEON_capable(void) {
-#if defined(__ARM_NEON__)
+  /* Only statically skip the runtime lookup on aarch64. On arm, one CPU is
+   * known to have a broken NEON unit which is known to fail with on some
+   * hand-written NEON assembly. For now, continue to apply the workaround even
+   * when the compiler is instructed to freely emit NEON code. See
+   * https://crbug.com/341598 and https://crbug.com/606629. */
+#if defined(__ARM_NEON__) && !defined(OPENSSL_ARM)
   return 1;
 #else
   return CRYPTO_is_NEON_capable_at_runtime();
 #endif
 }
 
+#if defined(OPENSSL_ARM)
+/* CRYPTO_has_broken_NEON returns one if the current CPU is known to have a
+ * broken NEON unit. See https://crbug.com/341598. */
+OPENSSL_EXPORT int CRYPTO_has_broken_NEON(void);
+#endif
+
 /* CRYPTO_is_ARMv8_AES_capable returns true if the current CPU supports the
  * ARMv8 AES instruction. */
 int CRYPTO_is_ARMv8_AES_capable(void);
@@ -152,7 +163,7 @@ static inline int CRYPTO_is_ARMv8_PMULL_capable(void) {
 }
 
 #endif  /* OPENSSL_STATIC_ARMCAP */
-#endif  /* OPENSSL_ARM */
+#endif  /* OPENSSL_ARM || OPENSSL_AARCH64 */
 
 
 #if defined(__cplusplus)