linux-kernel - [PATCH nolibc 51/61] tools/nolibc/string: do not use __builtin

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Date:   Mon, 18 Apr 2022 17:42:15 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     gwml@...r.gnuweeb.org, kernel-team@...com, w@....eu,
        Willy Tarreau <w@....eu>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH nolibc 51/61] tools/nolibc/string: do not use __builtin_strlen() at -O0

From: Willy Tarreau <w@....eu>

clang wants to use strlen() for __builtin_strlen() at -O0. We don't
really care about -O0 but it at least ought to build, so let's make
sure we don't choke on this, by dropping the optimizationn for
constant strings in this case.

Signed-off-by: Willy Tarreau <w@....eu>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 tools/include/nolibc/string.h | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/include/nolibc/string.h b/tools/include/nolibc/string.h
index 0d5e870c7c0b..75a453870498 100644
--- a/tools/include/nolibc/string.h
+++ b/tools/include/nolibc/string.h
@@ -122,7 +122,9 @@ char *strcpy(char *dst, const char *src)
 	return ret;
 }
 
-/* this function is only used with arguments that are not constants */
+/* this function is only used with arguments that are not constants or when
+ * it's not known because optimizations are disabled.
+ */
 static __attribute__((unused))
 size_t nolibc_strlen(const char *str)
 {
@@ -132,11 +134,18 @@ size_t nolibc_strlen(const char *str)
 	return len;
 }
 
+/* do not trust __builtin_constant_p() at -O0, as clang will emit a test and
+ * the two branches, then will rely on an external definition of strlen().
+ */
+#if defined(__OPTIMIZE__)
 #define strlen(str) ({                          \
 	__builtin_constant_p((str)) ?           \
 		__builtin_strlen((str)) :       \
 		nolibc_strlen((str));           \
 })
+#else
+#define strlen(str) nolibc_strlen((str))
+#endif
 
 static __attribute__((unused))
 size_t strlcat(char *dst, const char *src, size_t size)
-- 
2.31.1.189.g2e36527f23