[tip: timers/core] scripts: Fix the inclusion order in modpost

[tip-bot2 for Vincenzo Frascino]

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     f58dd03b1157bdf3b64c36e9525f8d7f69c25df2
Gitweb:        https://git.kernel.org/tip/f58dd03b1157bdf3b64c36e9525f8d7f69c25df2
Author:        Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
AuthorDate:    Fri, 20 Mar 2020 14:53:41 
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Sat, 21 Mar 2020 15:24:00 +01:00

scripts: Fix the inclusion order in modpost

In the process of creating the source file of a module modpost injects a
set of includes that are not required if the compilation unit is
statically built into the kernel.

The order of inclusion of the headers can cause redefinition problems
(e.g.):

   In file included from include/linux/elf.h:5:0,
                    from include/linux/module.h:18,
                    from crypto/arc4.mod.c:2:
    #define ELF_OSABI  ELFOSABI_LINUX

   In file included from include/linux/elfnote.h:62:0,
                    from include/linux/build-salt.h:4,
                    from crypto/arc4.mod.c:1:
   include/uapi/linux/elf.h:363:0: note: this is the location of
   the previous definition
    #define ELF_OSABI ELFOSABI_NONE

The issue was exposed during the development of the series [1].

[1] https://lore.kernel.org/lkml/20200306133242.26279-1-vincenzo.frascino@xxxxxxx/

Reported-by: kbuild test robot <lkp@xxxxxxxxx>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Cc: Michal Marek <michal.lkml@xxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200320145351.32292-17-vincenzo.frascino@xxxxxxx

---
 scripts/mod/modpost.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 7edfdb2..0f354b1 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -2251,8 +2251,12 @@ static int check_modname_len(struct module *mod)
  **/
 static void add_header(struct buffer *b, struct module *mod)
 {
-	buf_printf(b, "#include <linux/build-salt.h>\n");
 	buf_printf(b, "#include <linux/module.h>\n");
+	/*
+	 * Include build-salt.h after module.h in order to
+	 * inherit the definitions.
+	 */
+	buf_printf(b, "#include <linux/build-salt.h>\n");
 	buf_printf(b, "#include <linux/vermagic.h>\n");
 	buf_printf(b, "#include <linux/compiler.h>\n");
 	buf_printf(b, "\n");