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713a85195a
Small unsigned types are promoted to larger signed types in
the case of multiplication, the result of which may overflow.
In case the result of such a multiplication has its MSB
turned on, it will be sign extended with '1's.
This changes the multiplication result.
Code example of the phenomenon:
-------------------------------
u16 x, y;
size_t z1, z2;
x = y = 0xffff;
printk("x=%x y=%x\n",x,y);
z1 = x*y;
z2 = (size_t)x*y;
printk("z1=%lx z2=%lx\n", z1, z2);
Output:
-------
x=ffff y=ffff
z1=fffffffffffe0001 z2=fffe0001
The expected result of ffff*ffff is fffe0001, and without the
explicit casting to avoid the unwanted sign extension we got
fffffffffffe0001.
This commit adds an explicit casting to avoid the sign extension
issue.
Fixes:
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arch | ||
block | ||
certs | ||
crypto | ||
Documentation | ||
drivers | ||
fs | ||
include | ||
init | ||
io_uring | ||
ipc | ||
kernel | ||
lib | ||
LICENSES | ||
mm | ||
net | ||
rust | ||
samples | ||
scripts | ||
security | ||
sound | ||
tools | ||
usr | ||
virt | ||
.clang-format | ||
.cocciconfig | ||
.editorconfig | ||
.get_maintainer.ignore | ||
.gitattributes | ||
.gitignore | ||
.mailmap | ||
.rustfmt.toml | ||
COPYING | ||
CREDITS | ||
Kbuild | ||
Kconfig | ||
MAINTAINERS | ||
Makefile | ||
README |
Linux kernel ============ There are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. Please read Documentation/admin-guide/README.rst first. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. The formatted documentation can also be read online at: https://www.kernel.org/doc/html/latest/ There are various text files in the Documentation/ subdirectory, several of them using the reStructuredText markup notation. 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.