efi_loader: provide freestanding library

GCC requires that freestanding programs provide memcpy(), memmove(),
memset(), and memcmp().

Provide the required library functions.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>

lib/efi_loader/efi_freestanding.c

@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Library for freestanding binary
+ *
+ * Copyright 2019, Heinrich Schuchardt <xypron.glpk@gmx.de>
+ *
+ * GCC requires that freestanding programs provide memcpy(), memmove(),
+ * memset(), and memcmp().
+ */
+
+#include <common.h>
+
+/**
+ * memcmp() - compare memory areas
+ *
+ * @s1:		pointer to first area
+ * @s2:		pointer to second area
+ * @n:		number of bytes to compare
+ * Return:	0 if both memory areas are the same, otherwise the sign of the
+ *		result value is the same as the sign of the difference between
+ *		the first differing pair of bytes taken as u8.
+ */
+int memcmp(const void *s1, const void *s2, size_t n)
+{
+	const u8 *pos1 = s1;
+	const u8 *pos2 = s2;
+
+	for (; n; --n) {
+		if (*pos1 != *pos2)
+			return *pos1 - *pos2;
+		++pos1;
+		++pos2;
+	}
+	return 0;
+}
+
+/**
+ * memcpy() - copy memory area
+ *
+ * @dest:	destination buffer
+ * @src:	source buffer
+ * @n:		number of bytes to copy
+ * Return:	pointer to destination buffer
+ */
+void *memmove(void *dest, const void *src, size_t n)
+{
+	u8 *d = dest;
+	const u8 *s = src;
+
+	if (d >= s) {
+		for (; n; --n)
+			*d++ = *s++;
+	} else {
+		d += n;
+		s += n;
+		for (; n; --n)
+			*--d = *--s;
+	}
+	return dest;
+}
+
+/**
+ * memcpy() - copy memory area
+ *
+ * @dest:	destination buffer
+ * @src:	source buffer
+ * @n:		number of bytes to copy
+ * Return:	pointer to destination buffer
+ */
+void *memcpy(void *dest, const void *src, size_t n)
+{
+	return memmove(dest, src, n);
+}
+
+/**
+ * memset() - fill memory with a constant byte
+ *
+ * @s:		destination buffer
+ * @c:		byte value
+ * @n:		number of bytes to set
+ * Return:	pointer to destination buffer
+ */
+void *memset(void *s, int c, size_t n)
+{
+	u8 *d = s;
+
+	for (; n; --n)
+		*d++ = c;
+	return s;
+}