1 files changed, 95 insertions, 0 deletions
diff --git a/src/port/pg_crc32c_armv8_choose.c b/src/port/pg_crc32c_armv8_choose.c
new file mode 100644
index 0000000..6443e6a
--- /dev/null
+++ b/src/port/pg_crc32c_armv8_choose.c
@@ -0,0 +1,95 @@
+/*-------------------------------------------------------------------------
+ *
+ * pg_crc32c_armv8_choose.c
+ *	  Choose between ARMv8 and software CRC-32C implementation.
+ *
+ * On first call, checks if the CPU we're running on supports the ARMv8
+ * CRC Extension. If it does, use the special instructions for CRC-32C
+ * computation. Otherwise, fall back to the pure software implementation
+ * (slicing-by-8).
+ *
+ * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/port/pg_crc32c_armv8_choose.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef FRONTEND
+#include "postgres.h"
+#else
+#include "postgres_fe.h"
+#endif
+
+#include <setjmp.h>
+#include <signal.h>
+
+#include "port/pg_crc32c.h"
+
+
+static sigjmp_buf illegal_instruction_jump;
+
+/*
+ * Probe by trying to execute pg_comp_crc32c_armv8().  If the instruction
+ * isn't available, we expect to get SIGILL, which we can trap.
+ */
+static void
+illegal_instruction_handler(SIGNAL_ARGS)
+{
+	siglongjmp(illegal_instruction_jump, 1);
+}
+
+static bool
+pg_crc32c_armv8_available(void)
+{
+	uint64		data = 42;
+	int			result;
+
+	/*
+	 * Be careful not to do anything that might throw an error while we have
+	 * the SIGILL handler set to a nonstandard value.
+	 */
+	pqsignal(SIGILL, illegal_instruction_handler);
+	if (sigsetjmp(illegal_instruction_jump, 1) == 0)
+	{
+		/* Rather than hard-wiring an expected result, compare to SB8 code */
+		result = (pg_comp_crc32c_armv8(0, &data, sizeof(data)) ==
+				  pg_comp_crc32c_sb8(0, &data, sizeof(data)));
+	}
+	else
+	{
+		/* We got the SIGILL trap */
+		result = -1;
+	}
+	pqsignal(SIGILL, SIG_DFL);
+
+#ifndef FRONTEND
+	/* We don't expect this case, so complain loudly */
+	if (result == 0)
+		elog(ERROR, "crc32 hardware and software results disagree");
+
+	elog(DEBUG1, "using armv8 crc32 hardware = %d", (result > 0));
+#endif
+
+	return (result > 0);
+}
+
+/*
+ * This gets called on the first call. It replaces the function pointer
+ * so that subsequent calls are routed directly to the chosen implementation.
+ */
+static pg_crc32c
+pg_comp_crc32c_choose(pg_crc32c crc, const void *data, size_t len)
+{
+	if (pg_crc32c_armv8_available())
+		pg_comp_crc32c = pg_comp_crc32c_armv8;
+	else
+		pg_comp_crc32c = pg_comp_crc32c_sb8;
+
+	return pg_comp_crc32c(crc, data, len);
+}
+
+pg_crc32c	(*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len) = pg_comp_crc32c_choose;