mirror of
https://github.com/torvalds/linux.git
synced 2026-08-01 03:59:40 +02:00
Linux kernel source tree
21fb26bfb0
Currrently we use a mixture of alternative sequences and static branches
to handle features detected at boot time. For ease of maintenance we
generally prefer to use static branches in C code, but this has a few
downsides:
* Each static branch has metadata in the __jump_table section, which is
not discarded after features are finalized. This wastes some space,
and slows down the patching of other static branches.
* The static branches are patched at a different point in time from the
alternatives, so changes are not atomic. This leaves a transient
period where there could be a mismatch between the behaviour of
alternatives and static branches, which could be problematic for some
features (e.g. pseudo-NMI).
* More (instrumentable) kernel code is executed to patch each static
branch, which can be risky when patching certain features (e.g.
irqflags management for pseudo-NMI).
* When CONFIG_JUMP_LABEL=n, static branches are turned into a load of a
flag and a conditional branch. This means it isn't safe to use such
static branches in an alternative address space (e.g. the NVHE/PKVM
hyp code), where the generated address isn't safe to acccess.
To deal with these issues, this patch introduces new
alternative_has_feature_*() helpers, which work like static branches but
are patched using alternatives. This ensures the patching is performed
at the same time as other alternative patching, allows the metadata to
be freed after patching, and is safe for use in alternative address
spaces.
Note that all supported toolchains have asm goto support, and since
commit:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| 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 | ||
| 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 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.