linux-kernel - [tip:x86/asm] x86, doc: Update uaccess.h comment to reflect clang changes

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Date:	Thu, 29 Aug 2013 13:42:35 -0700
From:	"tip-bot for H. Peter Anvin" <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	dl9pf@....de, tglx@...utronix.de, hpa@...ux.intel.com
Subject: [tip:x86/asm] x86, doc:
  Update uaccess.h comment to reflect clang changes

Commit-ID:  f69fa9a91f60fff6f2d8b658b7d84d235d9d89b7
Gitweb:     http://git.kernel.org/tip/f69fa9a91f60fff6f2d8b658b7d84d235d9d89b7
Author:     H. Peter Anvin <hpa@...ux.intel.com>
AuthorDate: Thu, 29 Aug 2013 13:34:50 -0700
Committer:  H. Peter Anvin <hpa@...ux.intel.com>
CommitDate: Thu, 29 Aug 2013 13:34:50 -0700

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: H. Peter Anvin <hpa@...ux.intel.com>
Cc: Jan-Simon Möller <dl9pf@....de>
---
 arch/x86/include/asm/uaccess.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index f715fee..5838fa9 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -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)						\
 ({									\
--
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