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Instead of inlining the stac/mov/clac sequence (which also requires individual exception table entries and several asm instruction alternatives entries), just generate "call __put_user_nocheck_X" for the __put_user() cases, the same way we changed __get_user earlier. Unlike the get_user() case, we didn't have the same nice infrastructure to just generate the call with a single case, so this actually has to change some of the infrastructure in order to do this. But that only cleans up the code further. So now, instead of using a case statement for the sizes, we just do the same thing we've done on the get_user() side for a long time: use the size as an immediate constant to the asm, and generate the asm that way directly. In order to handle the special case of 64-bit data on a 32-bit kernel, I needed to change the calling convention slightly: the data is passed in %eax[:%edx], the pointer in %ecx, and the return value is also returned in %ecx. It used to be returned in %eax, but because of how %eax can now be a double register input, we don't want mix that with a single-register output. The actual low-level asm is easier to handle: we'll just share the code between the checking and non-checking case, with the non-checking case jumping into the middle of the function. That may sound a bit too special, but this code is all very very special anyway, so... Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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 Restructured Text 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.