arm64: Implement baremetal OPENSSL_cpuid_setup

Provide an implementation of OPENSSL_cpuid_setup() which identifies the
available CPU features required by the library directly from the system
registers for baremetal AArch64 builds without static initializer
(OPENSSL_NO_STATIC_INITIALIZER) that don't configure static capabilities
(OPENSSL_STATIC_ARMCAP). This assumes that the client code is NOT
running at exception level EL0 (userspace) and is enabled for
ANDROID_BAREMETAL.

Bug: b:265125189
Change-Id: Ifee6fbd24ece823a4661dd984f89473e1e1e3eda
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/58586
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: Bob Beck <bbe@google.com>

crypto/CMakeLists.txt

diff --git a/crypto/CMakeLists.txt b/crypto/CMakeLists.txt
index f0c892f..c7eb598 100644
--- a/crypto/CMakeLists.txt
+++ b/crypto/CMakeLists.txt
@@ -131,6 +131,7 @@
   cpu_aarch64_openbsd.c
   cpu_aarch64_fuchsia.c
   cpu_aarch64_linux.c
+  cpu_aarch64_sysreg.c
   cpu_aarch64_win.c
   cpu_arm_freebsd.c
   cpu_arm_openbsd.c

crypto/cpu_aarch64_sysreg.c

diff --git a/crypto/cpu_aarch64_sysreg.c b/crypto/cpu_aarch64_sysreg.c
new file mode 100644
index 0000000..8f85e8a
--- /dev/null
+++ b/crypto/cpu_aarch64_sysreg.c
@@ -0,0 +1,91 @@
+/* Copyright (c) 2023, Google Inc.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
+
+#include "internal.h"
+
+#if defined(OPENSSL_AARCH64) && !defined(OPENSSL_STATIC_ARMCAP) && \
+    defined(ANDROID_BAREMETAL)
+
+#include <openssl/arm_arch.h>
+
+#define ID_AA64PFR0_EL1_ADVSIMD 5
+
+#define ID_AA64ISAR0_EL1_AES 1
+#define ID_AA64ISAR0_EL1_SHA1 2
+#define ID_AA64ISAR0_EL1_SHA2 3
+
+#define NBITS_ID_FIELD 4
+
+#define READ_SYSREG(name)                \
+  ({                                     \
+    uint64_t _r;                         \
+    __asm__("mrs %0, " name : "=r"(_r)); \
+    _r;                                  \
+  })
+
+static unsigned get_id_field(uint64_t reg, unsigned field) {
+  return (reg >> (field * NBITS_ID_FIELD)) & ((1 << NBITS_ID_FIELD) - 1);
+}
+
+static int get_signed_id_field(uint64_t reg, unsigned field) {
+  unsigned value = get_id_field(reg, field);
+  if (value & (1 << (NBITS_ID_FIELD - 1))) {
+    return (int)(value | (UINT64_MAX << NBITS_ID_FIELD));
+  } else {
+    return (int)value;
+  }
+}
+
+static uint32_t read_armcap(void) {
+  uint32_t armcap = ARMV7_NEON;
+
+  uint64_t id_aa64pfr0_el1 = READ_SYSREG("id_aa64pfr0_el1");
+
+  if (get_signed_id_field(id_aa64pfr0_el1, ID_AA64PFR0_EL1_ADVSIMD) < 0) {
+    // If AdvSIMD ("NEON") is missing, don't report other features either.
+    // This matches OpenSSL.
+    return 0;
+  }
+
+  uint64_t id_aa64isar0_el1 = READ_SYSREG("id_aa64isar0_el1");
+
+  unsigned aes = get_id_field(id_aa64isar0_el1, ID_AA64ISAR0_EL1_AES);
+  if (aes > 0) {
+    armcap |= ARMV8_AES;
+  }
+  if (aes > 1) {
+    armcap |= ARMV8_PMULL;
+  }
+
+  unsigned sha1 = get_id_field(id_aa64isar0_el1, ID_AA64ISAR0_EL1_SHA1);
+  if (sha1 > 0) {
+    armcap |= ARMV8_SHA1;
+  }
+
+  unsigned sha2 = get_id_field(id_aa64isar0_el1, ID_AA64ISAR0_EL1_SHA2);
+  if (sha2 > 0) {
+    armcap |= ARMV8_SHA256;
+  }
+  if (sha2 > 1) {
+    armcap |= ARMV8_SHA512;
+  }
+
+  return armcap;
+}
+
+extern uint32_t OPENSSL_armcap_P;
+
+void OPENSSL_cpuid_setup(void) { OPENSSL_armcap_P |= read_armcap(); }
+
+#endif  // OPENSSL_AARCH64 && !OPENSSL_STATIC_ARMCAP && ANDROID_BAREMETAL