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Clang tries to warn when there's a mismatch between an operand's size,
and the size of the register it is held in, as this may indicate a bug.
Specifically, clang warns when the operand's type is less than 64 bits
wide, and the register is used unqualified (i.e. %N rather than %xN or
%wN).
Unfortunately clang can generate these warnings for unreachable code.
For example, for code like:
do { \
typeof(*(ptr)) __v = (v); \
switch(sizeof(*(ptr))) { \
case 1: \
// assume __v is 1 byte wide \
asm ("{op}b %w0" : : "r" (v)); \
break; \
case 8: \
// assume __v is 8 bytes wide \
asm ("{op} %0" : : "r" (v)); \
break; \
}
while (0)
... if op() were passed a char value and pointer to char, clang may
produce a warning for the unreachable case where sizeof(*(ptr)) is 8.
For the same reasons, clang produces warnings when __put_user_err() is
used for types that are less than 64 bits wide.
We could avoid this with a cast to a fixed-width type in each of the
cases. However, GCC will then warn that pointer types are being cast to
mismatched integer sizes (in unreachable paths).
Another option would be to use the same union trickery as we do for
__smp_store_release() and __smp_load_acquire(), but this is fairly
invasive.
Instead, this patch suppresses the clang warning by using an x modifier
in the assembly for the 8 byte case of __put_user_err(). No additional
work is necessary as the value has been cast to typeof(*(ptr)), so the
compiler will have performed any necessary extension for the reachable
case.
For consistency, __get_user_err() is also updated to use the x modifier
for its 8 byte case.
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reported-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
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| kernel | ||
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| .mailmap | ||
| COPYING | ||
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| Kbuild | ||
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| Makefile | ||
| README | ||
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.