Make const ptr assign as function call in clang

- This can act as memory barrier in clang to avoid
  read before assign of a const ptr

Signed-off-by: LoveSy <shana@zju.edu.cn>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

libbb/Kbuild.src

@@ -24,6 +24,7 @@ lib-y += chomp.o
 lib-y += compare_string_array.o
 lib-y += concat_path_file.o
 lib-y += concat_subpath_file.o
+lib-y += const_hack.o
 lib-y += copy_file.o
 lib-y += copyfd.o
 lib-y += crc32.o

libbb/appletlib.c

@@ -247,7 +247,7 @@ void lbb_prepare(const char *applet
 		IF_FEATURE_INDIVIDUAL(, char **argv))
 {
 #ifdef bb_cached_errno_ptr
-	ASSIGN_CONST_PTR(bb_errno, get_perrno());
+	ASSIGN_CONST_PTR(&bb_errno, get_perrno());
 #endif
 	applet_name = applet;
 

libbb/const_hack.c

@@ -0,0 +1,16 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Trick to assign a const ptr with barrier for clang
+ *
+ * Copyright (C) 2021 by YU Jincheng <shana@zju.edu.cn>
+ *
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
+ */
+#include "libbb.h"
+
+#if defined(__clang_major__) && __clang_major__ >= 9
+void FAST_FUNC XZALLOC_CONST_PTR(const void *pptr, size_t size)
+{
+	ASSIGN_CONST_PTR(pptr, xzalloc(size));
+}
+#endif

libbb/lineedit.c

@@ -214,7 +214,7 @@ extern struct lineedit_statics *BB_GLOBAL_CONST lineedit_ptr_to_statics;
 #define delbuf           (S.delbuf          )
 
 #define INIT_S() do { \
-	ASSIGN_CONST_PTR(lineedit_ptr_to_statics, xzalloc(sizeof(S))); \
+	XZALLOC_CONST_PTR(&lineedit_ptr_to_statics, sizeof(S)); \
 } while (0)
 
 static void deinit_S(void)