efi: libstub: Provide local implementations of strrchr() and memchr()

Clone the implementations of strrchr() and memchr() in lib/string.c so
we can use them in the standalone zboot decompressor app. These routines
are used by the FDT handling code.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/libstub/string.c

@@ -64,6 +64,28 @@ char *strstr(const char *s1, const char *s2)
 	return NULL;
 }
 
+#ifndef EFI_HAVE_STRCMP
+/**
+ * strcmp - Compare two strings
+ * @cs: One string
+ * @ct: Another string
+ */
+int strcmp(const char *cs, const char *ct)
+{
+	unsigned char c1, c2;
+
+	while (1) {
+		c1 = *cs++;
+		c2 = *ct++;
+		if (c1 != c2)
+			return c1 < c2 ? -1 : 1;
+		if (!c1)
+			break;
+	}
+	return 0;
+}
+#endif
+
 /**
  * strncmp - Compare two length-limited strings
  * @cs: One string
@@ -140,3 +162,43 @@ long simple_strtol(const char *cp, char **endp, unsigned int base)
 
 	return simple_strtoull(cp, endp, base);
 }
+
+#ifdef CONFIG_EFI_PARAMS_FROM_FDT
+#ifndef EFI_HAVE_STRRCHR
+/**
+ * strrchr - Find the last occurrence of a character in a string
+ * @s: The string to be searched
+ * @c: The character to search for
+ */
+char *strrchr(const char *s, int c)
+{
+	const char *last = NULL;
+	do {
+		if (*s == (char)c)
+			last = s;
+	} while (*s++);
+	return (char *)last;
+}
+#endif
+#ifndef EFI_HAVE_MEMCHR
+/**
+ * memchr - Find a character in an area of memory.
+ * @s: The memory area
+ * @c: The byte to search for
+ * @n: The size of the area.
+ *
+ * returns the address of the first occurrence of @c, or %NULL
+ * if @c is not found
+ */
+void *memchr(const void *s, int c, size_t n)
+{
+	const unsigned char *p = s;
+	while (n-- != 0) {
+		if ((unsigned char)c == *p++) {
+			return (void *)(p - 1);
+		}
+	}
+	return NULL;
+}
+#endif
+#endif