tools/nolibc: add missing memchr() to string.h

Surprisingly we forgot to add this common one. It was added with a
per-arch guard allowing to later implement it in arch-specific asm
code like was done for a few other ones.

The test verifies that we don't search past the indicated length.

Signed-off-by: Willy Tarreau <[e-mail]>
Signed-off-by: Thomas Weißschuh <[e-mail]>

tools/include/nolibc/string.h

···
 }
 #endif /* #ifndef NOLIBC_ARCH_HAS_MEMSET */
 
+#ifndef NOLIBC_ARCH_HAS_MEMCHR
+static __attribute__((unused))
+void *memchr(const void *s, int c, size_t len)
+{
+	char *p = (char *)s;
+
+	while (len--) {
+		if (*p == (char)c)
+			return p;
+		p++;
+	}
+	return NULL;
+}
+#endif /* #ifndef NOLIBC_ARCH_HAS_MEMCHR */
+
 static __attribute__((unused))
 char *strchr(const char *s, int c)
 {

tools/testing/selftests/nolibc/nolibc-test.c

···
 		CASE_TEST(abs);                     EXPECT_EQ(1, abs(-10), 10); break;
 		CASE_TEST(abs_noop);                EXPECT_EQ(1, abs(10), 10); break;
 		CASE_TEST(difftime);                EXPECT_ZR(1, test_difftime()); break;
+		CASE_TEST(memchr_foobar6_o);        EXPECT_STREQ(1, memchr("foobar", 'o', 6), "oobar"); break;
+		CASE_TEST(memchr_foobar3_b);        EXPECT_STRZR(1, memchr("foobar", 'b', 3)); break;
 
 		case __LINE__:
 			return ret; /* must be last */