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Commit f69fa9a9 authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

x86, doc: Update uaccess.h comment to reflect clang changes 

Update comment in uaccess.h to reflect the changes for clang support:
gcc only cares about the base register (most architectures don't
encode the size of the operation in the operands like x86 does, and so
it is treated effectively like a register number), whereas clang tries
to enforce the size -- but not for register pairs.

Link: http://lkml.kernel.org/r/1377803585-5913-3-git-send-email-dl9pf@gmx.de


Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
Cc: Jan-Simon Möller <dl9pf@gmx.de>
parent bdfc017e

arch/x86/include/asm/uaccess.h

+4 −1
Original line number Diff line number Diff line
@@ -153,11 +153,14 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL)) 
 * Careful: we have to cast the result to the type of the pointer

 * for sign reasons.

 *

 * The use of %edx as the register specifier is a bit of a

 * The use of _ASM_DX as the register specifier is a bit of a

 * simplification, as gcc only cares about it as the starting point

 * and not size: for a 64-bit value it will use %ecx:%edx on 32 bits

 * (%ecx being the next register in gcc's x86 register sequence), and

 * %rdx on 64 bits.

 *

 * Clang/LLVM cares about the size of the register, but still wants

 * the base register for something that ends up being a pair.

 */

#define get_user(x, ptr)						\

({									\