[RFC PATCH v2 8/8] tools/include/string: Implement `strdup()` and `strndup()`

[Ammar Faizi <ammarfaizi2@gnuweeb.org>]

These functions are currently only available on architectures that have
my_syscall6() macro implemented. Since these functions use malloc(),
malloc() uses mmap(), mmap() depends on my_syscall6() macro.

On architectures that don't support my_syscall6(), these function will
always return NULL with errno set to ENOSYS.

Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
---

@@ Changelog:

   Link RFC v1: https://lore.kernel.org/lkml/20220320093750.159991-7-ammarfaizi2@gnuweeb.org/
   RFC v1 -> RFC v2:
    - Update strdup and strndup implementation, use strlen and strnlen to get
      the string length first (comment from Willy and Alviro).
    - Fix the subject line prefix, it was "tools/include/string: ", it should be
      "tools/nolibc/string: ".
    - Update the commit message.
---
 tools/include/nolibc/string.h | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/tools/include/nolibc/string.h b/tools/include/nolibc/string.h
index 1426eefc1ef2..bcc76f89199e 100644
--- a/tools/include/nolibc/string.h
+++ b/tools/include/nolibc/string.h
@@ -9,6 +9,8 @@
 
 #include "std.h"
 
+static void *malloc(size_t len);
+
 /*
  * As much as possible, please keep functions alphabetically sorted.
  */
@@ -147,6 +149,36 @@ size_t strnlen(const char *str, size_t maxlen)
 	return len;
 }
 
+static __attribute__((unused))
+char *strdup(const char *str)
+{
+	size_t len;
+	char *ret;
+
+	len = strlen(str);
+	ret = malloc(len + 1);
+	if (__builtin_expect(ret != NULL, 1))
+		memcpy(ret, str, len + 1);
+
+	return ret;
+}
+
+static __attribute__((unused))
+char *strndup(const char *str, size_t maxlen)
+{
+	size_t len;
+	char *ret;
+
+	len = strnlen(str, maxlen);
+	ret = malloc(len + 1);
+	if (__builtin_expect(ret != NULL, 1)) {
+		memcpy(ret, str, len);
+		ret[len] = '\0';
+	}
+
+	return ret;
+}
+
 static __attribute__((unused))
 size_t strlcat(char *dst, const char *src, size_t size)
 {
-- 
Ammar Faizi