mainlining shenanigans
a46349227c
Add BPF static linker logic to resolve extern variables and functions across multiple linked together BPF object files. For that, linker maintains a separate list of struct glob_sym structures, which keeps track of few pieces of metadata (is it extern or resolved global, is it a weak symbol, which ELF section it belongs to, etc) and ties together BTF type info and ELF symbol information and keeps them in sync. With adding support for extern variables/funcs, it's now possible for some sections to contain both extern and non-extern definitions. This means that some sections may start out as ephemeral (if only externs are present and thus there is not corresponding ELF section), but will be "upgraded" to actual ELF section as symbols are resolved or new non-extern definitions are appended. Additional care is taken to not duplicate extern entries in sections like .kconfig and .ksyms. Given libbpf requires BTF type to always be present for .kconfig/.ksym externs, linker extends this requirement to all the externs, even those that are supposed to be resolved during static linking and which won't be visible to libbpf. With BTF information always present, static linker will check not just ELF symbol matches, but entire BTF type signature match as well. That logic is stricter that BPF CO-RE checks. It probably should be re-used by .ksym resolution logic in libbpf as well, but that's left for follow up patches. To make it unnecessary to rewrite ELF symbols and minimize BTF type rewriting/removal, ELF symbols that correspond to externs initially will be updated in place once they are resolved. Similarly for BTF type info, VAR/FUNC and var_secinfo's (sec_vars in struct bpf_linker) are staying stable, but types they point to might get replaced when extern is resolved. This might leave some left-over types (even though we try to minimize this for common cases of having extern funcs with not argument names vs concrete function with names properly specified). That can be addresses later with a generic BTF garbage collection. That's left for a follow up as well. Given BTF type appending phase is separate from ELF symbol appending/resolution, special struct glob_sym->underlying_btf_id variable is used to communicate resolution and rewrite decisions. 0 means underlying_btf_id needs to be appended (it's not yet in final linker->btf), <0 values are used for temporary storage of source BTF type ID (not yet rewritten), so -glob_sym->underlying_btf_id is BTF type id in obj-btf. But by the end of linker_append_btf() phase, that underlying_btf_id will be remapped and will always be > 0. This is the uglies part of the whole process, but keeps the other parts much simpler due to stability of sec_var and VAR/FUNC types, as well as ELF symbol, so please keep that in mind while reviewing. BTF-defined maps require some extra custom logic and is addressed separate in the next patch, so that to keep this one smaller and easier to review. Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Yonghong Song <yhs@fb.com> Link: https://lore.kernel.org/bpf/20210423181348.1801389-12-andrii@kernel.org |
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| 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 | ||
| 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.