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

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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@linux.intel.com>
Cc: Jan-Simon Möller <dl9pf@gmx.de>
This commit is contained in:
H. Peter Anvin 2013-08-29 13:34:50 -07:00
parent bdfc017eea
commit f69fa9a91f
1 changed files with 4 additions and 1 deletions
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arch/x86/include/asm/uaccess.h
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@ -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) \
({ \