[PATCH] RISC-V: Don't use a global include guard for uapi/asm/syscalls.h

[Palmer Dabbelt]

This file is expected to be included multiple times in the same file in
order to allow the __SYSCALL macro to generate system call tables.  With
a global include guard we end up missing __NR_riscv_flush_icache in the
syscall table, which results in icache flushes that escape the vDSO call
to not actually do anything.

The fix is to move to per-#define include guards, which allows the
system call tables to actually be populated.  Thanks to Macrus Comstedt
for finding and fixing the bug!

I also went ahead and fixed the SPDX header to use a //-style comment,
which I've been told is the canonical way to do it.

Cc: Marcus Comstedt <marcus@xxxxxxxx>
Signed-off-by: Palmer Dabbelt <palmer@xxxxxxxxxx>
---
 arch/riscv/include/uapi/asm/syscalls.h | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/riscv/include/uapi/asm/syscalls.h b/arch/riscv/include/uapi/asm/syscalls.h
index 818655b0d535..882a6aa09a33 100644
--- a/arch/riscv/include/uapi/asm/syscalls.h
+++ b/arch/riscv/include/uapi/asm/syscalls.h
@@ -1,10 +1,11 @@
-/* SPDX-License-Identifier: GPL-2.0 */
+// SPDX-License-Identifier: GPL-2.0
 /*
- * Copyright (C) 2017 SiFive
+ * Copyright (C) 2017-2018 SiFive
  */
 
-#ifndef _ASM__UAPI__SYSCALLS_H
-#define _ASM__UAPI__SYSCALLS_H
+/* There is explicitly no include guard here because this file is expected to
+ * be included multiple times in order to define the syscall macros via
+ * __SYSCALL. */
 
 /*
  * Allows the instruction cache to be flushed from userspace.  Despite RISC-V
@@ -20,7 +21,7 @@
  * caller.  We don't currently do anything with the address range, that's just
  * in there for forwards compatibility.
  */
+#ifndef __NR_riscv_flush_icache
 #define __NR_riscv_flush_icache (__NR_arch_specific_syscall + 15)
-__SYSCALL(__NR_riscv_flush_icache, sys_riscv_flush_icache)
-
 #endif
+__SYSCALL(__NR_riscv_flush_icache, sys_riscv_flush_icache)
-- 
2.16.4