plat/arm: juno: Condition Juno entropy source with CRC instructions
The Juno Trusted Entropy Source has a bias, which makes the generated
raw numbers fail a FIPS 140-2 statistic test.
To improve the quality of the numbers, we can use the CPU's CRC
instructions, which do a decent job on conditioning the bits.
This adds a *very* simple version of arm_acle.h, which is typically
provided by the compiler, and contains the CRC instrinsics definitions
we need. We need the original version by using -nostdinc.
Change-Id: I83d3e6902d6a1164aacd5060ac13a38f0057bd1a
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/include/lib/libc/arm_acle.h b/include/lib/libc/arm_acle.h
new file mode 100644
index 0000000..953933f
--- /dev/null
+++ b/include/lib/libc/arm_acle.h
@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2021 ARM Limited
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * The definitions below are a subset of what we would normally get by using
+ * the compiler's version of arm_acle.h. We can't use that directly because
+ * we specify -nostdinc in the Makefiles.
+ *
+ * We just define the functions we need so far.
+ */
+
+#ifndef ARM_ACLE_H
+#define ARM_ACLE_H
+
+#if !defined(__aarch64__) || defined(__clang__)
+# define __crc32w __builtin_arm_crc32w
+#else
+# define __crc32w __builtin_aarch64_crc32w
+#endif
+
+#endif /* ARM_ACLE_H */