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It is better to clear as many flags as possible when we do a system call entry, as opposed to the other way around. The fewer flags we keep, the lesser the possible interference between the kernel and user space. The flags changed are: - CF, PF, AF, ZF, SF, OF: these are arithmetic flags which affect branches, possibly speculatively. They should be cleared for the same reasons we now clear all GPRs on entry. - RF: suppresses a code breakpoint on the subsequent instruction. It is probably impossible to enter the kernel with RF set, but if it is somehow not, it would break a kernel debugger setting a breakpoint on the entry point. Either way, user space should not be able to control kernel behavior here. - ID: this flag has no direct effect (it is a scratch bit only.) However, there is no reason to retain the user space value in the kernel, and the standard should be to clear unless needed, not the other way around. Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20210510185316.3307264-5-hpa@zytor.com |
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| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
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| 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 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.