Commit a76cf66e authored Oct 05, 2015 by Andy Lutomirski Committed by Ingo Molnar Oct 07, 2015

x86/uaccess: Tell the compiler that uaccess is unlikely to fault



GCC doesn't realize that get_user(), put_user(), and their __
variants are unlikely to fail.  Tell it.

I noticed this while playing with the C entry code.

 Before:
       text     data      bss       dec    filename
   21828763  5194760  1277952  28301475    vmlinux.baseline

 After:
      text      data      bss       dec    filename
   21828379  5194760  1277952  28301091    vmlinux.new

The generated code shrunk by 384 bytes.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/dc37bed7024319c3004d950d57151fca6aeacf97.1444091584.git.luto@kernel.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 25a9a924

arch/x86/include/asm/uaccess.h

+4 −4

Original line number	Diff line number	Diff line
		@@ -182,7 +182,7 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
		: "=a" (__ret_gu), "=r" (__val_gu) \
		: "0" (ptr), "i" (sizeof(*(ptr)))); \
		(x) = (__force __typeof__(*(ptr))) __val_gu; \
		__ret_gu; \
		__builtin_expect(__ret_gu, 0); \
		})

		#define __put_user_x(size, x, ptr, __ret_pu) \
		@@ -278,7 +278,7 @@ extern void __put_user_8(void);
		__put_user_x(X, __pu_val, ptr, __ret_pu); \
		break; \
		} \
		__ret_pu; \
		__builtin_expect(__ret_pu, 0); \
		})

		#define __put_user_size(x, ptr, size, retval, errret) \
		@@ -401,7 +401,7 @@ do { \
		({ \
		int __pu_err; \
		__put_user_size((x), (ptr), (size), __pu_err, -EFAULT); \
		__pu_err; \
		__builtin_expect(__pu_err, 0); \
		})

		#define __get_user_nocheck(x, ptr, size) \
		@@ -410,7 +410,7 @@ do { \
		unsigned long __gu_val; \
		__get_user_size(__gu_val, (ptr), (size), __gu_err, -EFAULT); \
		(x) = (__force __typeof__(*(ptr)))__gu_val; \
		__gu_err; \
		__builtin_expect(__gu_err, 0); \
		})

		/* FIXME: this hack is definitely wrong -AK */