mainlining shenanigans
7d3c107706
Andrii Nakryiko says:
====================
Add BPF static linker support for extern resolution of global variables,
functions, and BTF-defined maps.
This patch set consists of 4 parts:
- few patches are extending bpftool to simplify working with BTF dump;
- libbpf object loading logic is extended to support __hidden functions and
overriden (unused) __weak functions; also BTF-defined map parsing logic is
refactored to be re-used by linker;
- the crux of the patch set is BPF static linker logic extension to perform
extern resolution for three categories: global variables, BPF
sub-programs, BTF-defined maps;
- a set of selftests that validate that all the combinations of
extern/weak/__hidden are working as expected.
See respective patches for more details.
One aspect hasn't been addressed yet and is going to be resolved in the next
patch set, but is worth mentioning. With BPF static linking of multiple .o
files, dealing with static everything becomes more problematic for BPF
skeleton and in general for any by name look up APIs. This is due to static
entities are allowed to have non-unique name. Historically this was never
a problem due to BPF programs were always confined to a single C file. That
changes now and needs to be addressed. The thinking so far is for BPF static
linker to prepend filename to each static variable and static map (which is
currently not supported by libbpf, btw), so that they can be unambiguously
resolved by (mostly) unique name. Mostly, because even filenames can be
duplicated, but that should be rare and easy to address by wiser choice of
filenames by users. Fortunately, static BPF subprograms don't suffer from this
issues, as they are not independent entities and are neither exposed in BPF
skeleton, nor is lookup-able by any of libbpf APIs (and there is little reason
to do that anyways).
This and few other things will be the topic of the next set of patches.
Some tests rely on Clang fix ([0]), so need latest Clang built from main.
[0] https://reviews.llvm.org/D100362
v2->v3:
- allow only STV_DEFAULT and STV_HIDDEN ELF symbol visibility (Yonghong);
- update selftests' README for required Clang 13 fix dependency (Alexei);
- comments, typos, slight code changes (Yonghong, Alexei);
v1->v2:
- make map externs support full attribute list, adjust linked_maps selftest
to demonstrate that typedef works now (though no shared header file was
added to simplicity sake) (Alexei);
- remove commented out parts from selftests and fix few minor code style
issues;
- special __weak map definition semantics not yet implemented and will be
addressed in a follow up.
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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| 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.