Remove almost all the code that explicitly iterated BPF program section
definitions in favor of using find_sec_def(). The only remaining user of
section_defs is libbpf_get_type_names that has to iterate all of them to
construct its result.
Having one internal API entry point for section definitions will
simplify further refactorings around libbpf's program section
definitions parsing.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20210914014733.2768-5-andrii@kernel.org
Remove the need to explicitly pass bpf_sec_def for auto-attachable BPF
programs, as it is already recorded at bpf_object__open() time for all
recognized type of BPF programs. This further reduces number of explicit
calls to find_sec_def(), simplifying further refactorings.
No functional changes are done by this patch.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20210914014733.2768-4-andrii@kernel.org
Refactor bpf_object__open() sequencing to perform BPF program type
detection based on SEC() definitions before we get to relocations
collection. This allows to have more information about BPF program by
the time we get to, say, struct_ops relocation gathering. This,
subsequently, simplifies struct_ops logic and removes the need to
perform extra find_sec_def() resolution.
With this patch libbpf will require all struct_ops BPF programs to be
marked with SEC("struct_ops") or SEC("struct_ops/xxx") annotations.
Real-world applications are already doing that through something like
selftests's BPF_STRUCT_OPS() macro. This change streamlines libbpf's
internal handling of SEC() definitions and is in the sprit of
upcoming libbpf-1.0 section strictness changes ([0]).
[0] https://github.com/libbpf/libbpf/wiki/Libbpf:-the-road-to-v1.0#stricter-and-more-uniform-bpf-program-section-name-sec-handling
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20210914014733.2768-3-andrii@kernel.org
Turn previously auto-generated libbpf_version.h header into a normal
header file. This prevents various tricky Makefile integration issues,
simplifies the overall build process, but also allows to further extend
it with some more versioning-related APIs in the future.
To prevent accidental out-of-sync versions as defined by libbpf.map and
libbpf_version.h, Makefile checks their consistency at build time.
Simultaneously with this change bump libbpf.map to v0.6.
Also undo adding libbpf's output directory into include path for
kernel/bpf/preload, bpftool, and resolve_btfids, which is not necessary
because libbpf_version.h is just a normal header like any other.
Fixes: 0b46b7550560 ("libbpf: Add LIBBPF_DEPRECATED_SINCE macro for scheduling API deprecations")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210913222309.3220849-1-andrii@kernel.org
Use this list of enabled tests as a whitelist, so that we don't have to
keep updating BLACKLIST-5.5.0 anymore. I'll keep BLACKLIST-5.5.0 for
now, because it serves as a nice historic log of which tests depend on
which kernels.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
When attaching to uprobes through perf subsystem, it's possible to specify
offset of a so-called USDT semaphore, which is just a reference counted u16,
used by kernel to keep track of how many tracers are attached to a given
location. Support for this feature was added in [0], so just wire this through
uprobe_opts. This is important to enable implementing USDT attachment and
tracing through libbpf's bpf_program__attach_uprobe_opts() API.
[0] a6ca88b241d5 ("trace_uprobe: support reference counter in fd-based uprobe")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210815070609.987780-16-andrii@kernel.org
Wire through bpf_cookie for all attach APIs that use perf_event_open under the
hood:
- for kprobes, extend existing bpf_kprobe_opts with bpf_cookie field;
- for perf_event, uprobe, and tracepoint APIs, add their _opts variants and
pass bpf_cookie through opts.
For kernel that don't support BPF_LINK_CREATE for perf_events, and thus
bpf_cookie is not supported either, return error and log warning for user.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210815070609.987780-12-andrii@kernel.org
Add ability to specify bpf_cookie value when creating BPF perf link with
bpf_link_create() low-level API.
Given BPF_LINK_CREATE command is growing and keeps getting new fields that are
specific to the type of BPF_LINK, extend libbpf side of bpf_link_create() API
and corresponding OPTS struct to accomodate such changes. Add extra checks to
prevent using incompatible/unexpected combinations of fields.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210815070609.987780-11-andrii@kernel.org
Detect kernel support for BPF perf link and prefer it when attaching to
perf_event, tracepoint, kprobe/uprobe. Underlying perf_event FD will be kept
open until BPF link is destroyed, at which point both perf_event FD and BPF
link FD will be closed.
This preserves current behavior in which perf_event FD is open for the
duration of bpf_link's lifetime and user is able to "disconnect" bpf_link from
underlying FD (with bpf_link__disconnect()), so that bpf_link__destroy()
doesn't close underlying perf_event FD.When BPF perf link is used, disconnect
will keep both perf_event and bpf_link FDs open, so it will be up to
(advanced) user to close them. This approach is demonstrated in bpf_cookie.c
selftests, added in this patch set.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210815070609.987780-10-andrii@kernel.org
bpf_link->destroy() isn't used by any code, so remove it. Instead, add ability
to override deallocation procedure, with default doing plain free(link). This
is necessary for cases when we want to "subclass" struct bpf_link to keep
extra information, as is the case in the next patch adding struct
bpf_link_perf.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210815070609.987780-9-andrii@kernel.org
Add new BPF helper, bpf_get_attach_cookie(), which can be used by BPF programs
to get access to a user-provided bpf_cookie value, specified during BPF
program attachment (BPF link creation) time.
Naming is hard, though. With the concept being named "BPF cookie", I've
considered calling the helper:
- bpf_get_cookie() -- seems too unspecific and easily mistaken with socket
cookie;
- bpf_get_bpf_cookie() -- too much tautology;
- bpf_get_link_cookie() -- would be ok, but while we create a BPF link to
attach BPF program to BPF hook, it's still an "attachment" and the
bpf_cookie is associated with BPF program attachment to a hook, not a BPF
link itself. Technically, we could support bpf_cookie with old-style
cgroup programs.So I ultimately rejected it in favor of
bpf_get_attach_cookie().
Currently all perf_event-backed BPF program types support
bpf_get_attach_cookie() helper. Follow-up patches will add support for
fentry/fexit programs as well.
While at it, mark bpf_tracing_func_proto() as static to make it obvious that
it's only used from within the kernel/trace/bpf_trace.c.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210815070609.987780-7-andrii@kernel.org
Add ability for users to specify custom u64 value (bpf_cookie) when creating
BPF link for perf_event-backed BPF programs (kprobe/uprobe, perf_event,
tracepoints).
This is useful for cases when the same BPF program is used for attaching and
processing invocation of different tracepoints/kprobes/uprobes in a generic
fashion, but such that each invocation is distinguished from each other (e.g.,
BPF program can look up additional information associated with a specific
kernel function without having to rely on function IP lookups). This enables
new use cases to be implemented simply and efficiently that previously were
possible only through code generation (and thus multiple instances of almost
identical BPF program) or compilation at runtime (BCC-style) on target hosts
(even more expensive resource-wise). For uprobes it is not even possible in
some cases to know function IP before hand (e.g., when attaching to shared
library without PID filtering, in which case base load address is not known
for a library).
This is done by storing u64 bpf_cookie in struct bpf_prog_array_item,
corresponding to each attached and run BPF program. Given cgroup BPF programs
already use two 8-byte pointers for their needs and cgroup BPF programs don't
have (yet?) support for bpf_cookie, reuse that space through union of
cgroup_storage and new bpf_cookie field.
Make it available to kprobe/tracepoint BPF programs through bpf_trace_run_ctx.
This is set by BPF_PROG_RUN_ARRAY, used by kprobe/uprobe/tracepoint BPF
program execution code, which luckily is now also split from
BPF_PROG_RUN_ARRAY_CG. This run context will be utilized by a new BPF helper
giving access to this user-provided cookie value from inside a BPF program.
Generic perf_event BPF programs will access this value from perf_event itself
through passed in BPF program context.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/bpf/20210815070609.987780-6-andrii@kernel.org
Introduce a new type of BPF link - BPF perf link. This brings perf_event-based
BPF program attachments (perf_event, tracepoints, kprobes, and uprobes) into
the common BPF link infrastructure, allowing to list all active perf_event
based attachments, auto-detaching BPF program from perf_event when link's FD
is closed, get generic BPF link fdinfo/get_info functionality.
BPF_LINK_CREATE command expects perf_event's FD as target_fd. No extra flags
are currently supported.
Force-detaching and atomic BPF program updates are not yet implemented, but
with perf_event-based BPF links we now have common framework for this without
the need to extend ioctl()-based perf_event interface.
One interesting consideration is a new value for bpf_attach_type, which
BPF_LINK_CREATE command expects. Generally, it's either 1-to-1 mapping from
bpf_attach_type to bpf_prog_type, or many-to-1 mapping from a subset of
bpf_attach_types to one bpf_prog_type (e.g., see BPF_PROG_TYPE_SK_SKB or
BPF_PROG_TYPE_CGROUP_SOCK). In this case, though, we have three different
program types (KPROBE, TRACEPOINT, PERF_EVENT) using the same perf_event-based
mechanism, so it's many bpf_prog_types to one bpf_attach_type. I chose to
define a single BPF_PERF_EVENT attach type for all of them and adjust
link_create()'s logic for checking correspondence between attach type and
program type.
The alternative would be to define three new attach types (e.g., BPF_KPROBE,
BPF_TRACEPOINT, and BPF_PERF_EVENT), but that seemed like unnecessary overkill
and BPF_KPROBE will cause naming conflicts with BPF_KPROBE() macro, defined by
libbpf. I chose to not do this to avoid unnecessary proliferation of
bpf_attach_type enum values and not have to deal with naming conflicts.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/bpf/20210815070609.987780-5-andrii@kernel.org
Kernel docs from Documentation/bpf/libbpf go straight to docs/ under libbpf.
Also ignore libbpf-only parts of docs subdir.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Only keep stderr output in case of errors for kernel and selftests builds.
Having a multi-thousand-line output isn't useful and slows down Github
Actions' log view UI.
Also quiet down wget's "progress bar" output. While at the same time see some
totals from tar, just for the fun of it.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Add few new selftests to blacklist. They can't succeed on 5.5.
Also temporarily remove btf_dump for 4.9 due to newly added data dumping
subtests.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Temporary disable tc_bpf tests that seem to have regressed.
Temporary and artificially bump pahole version from 1.21 to 1.22 to get
per-CPU BTF data built.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
We used to have it disabled for GCC8, but now GCC10 is false-report same
warnings, so disable stringop-truncation warnigs for GCC10 as well.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
This is necessary to make runqslower compile with task->__state field on old
kernels, for which we don't have an actual vmlinux.h.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Make sure we run all of the tests even if some of them fail. This allows to
test all of them independently, especially kernel LATEST slow test.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Implement changes to error reporting for high-level libbpf APIs to make them
less surprising and less error-prone to users:
- in all the cases when error happens, errno is set to an appropriate error
value;
- in libbpf 1.0 mode, all pointer-returning APIs return NULL on error and
error code is communicated through errno; this applies both to APIs that
already returned NULL before (so now they communicate more detailed error
codes), as well as for many APIs that used ERR_PTR() macro and encoded
error numbers as fake pointers.
- in legacy (default) mode, those APIs that were returning ERR_PTR(err),
continue doing so, but still set errno.
With these changes, errno can be always used to extract actual error,
regardless of legacy or libbpf 1.0 modes. This is utilized internally in
libbpf in places where libbpf uses it's own high-level APIs.
libbpf_get_error() is adapted to handle both cases completely transparently to
end-users (and is used by libbpf consistently as well).
More context, justification, and discussion can be found in "Libbpf: the road
to v1.0" document ([0]).
[0] https://docs.google.com/document/d/1UyjTZuPFWiPFyKk1tV5an11_iaRuec6U-ZESZ54nNTY
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20210525035935.1461796-5-andrii@kernel.org
Add libbpf_set_strict_mode() API that allows application to simulate libbpf
1.0 breaking changes before libbpf 1.0 is released. This will help users
migrate gradually and with confidence.
For now only ALL or NONE options are available, subsequent patches will add
more flags. This patch is preliminary for selftests/bpf changes.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20210525035935.1461796-2-andrii@kernel.org
Static maps never really worked with libbpf, because all such maps were always
silently resolved to the very first map. Detect static maps (both legacy and
BTF-defined) and report user-friendly error.
Tested locally by switching few maps (legacy and BTF-defined) in selftests to
static ones and verifying that now libbpf rejects them loudly.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210513233643.194711-2-andrii@kernel.org
For better future extensibility add per-file linker options. Currently
the set of available options is empty. This changes bpf_linker__add_file()
API, but it's not a breaking change as bpf_linker APIs hasn't been released
yet.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210507054119.270888-3-andrii@kernel.org
Add BTF_KIND_FLOAT support when doing CO-RE field type compatibility check.
Without this, relocations against float/double fields will fail.
Also adjust one error message to emit instruction index instead of less
convenient instruction byte offset.
Fixes: 22541a9eeb0d ("libbpf: Add BTF_KIND_FLOAT support")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Lorenz Bauer <lmb@cloudflare.com>
Link: https://lore.kernel.org/bpf/20210426192949.416837-3-andrii@kernel.org
Use aptitude to actually see what's wrong with the dependencies. And it
actually magically resolves whatever minor version conflicts there are.
The big surprise came from the apparent difference in build-dep command
behavior. Aptitude's build-dep doesn't seem to install the libpfelf-dev
package itself. Adding explicit `aptitude install libelf-dev` after build-dep
solves the issue for now.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Force libc6 dependency version.
Drop explicit libelf-dev install command, as it should be pre-installed by
Travis CI already, according to .travis.yaml.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Add extra logic to handle map externs (only BTF-defined maps are supported for
linking). Re-use the map parsing logic used during bpf_object__open(). Map
externs are currently restricted to always match complete map definition. So
all the specified attributes will be compared (down to pining, map_flags,
numa_node, etc). In the future this restriction might be relaxed with no
backwards compatibility issues. If any attribute is mismatched between extern
and actual map definition, linker will report an error, pointing out which one
mismatches.
The original intent was to allow for extern to specify attributes that matters
(to user) to enforce. E.g., if you specify just key information and omit
value, then any value fits. Similarly, it should have been possible to enforce
map_flags, pinning, and any other possible map attribute. Unfortunately, that
means that multiple externs can be only partially overlapping with each other,
which means linker would need to combine their type definitions to end up with
the most restrictive and fullest map definition. This requires an extra amount
of BTF manipulation which at this time was deemed unnecessary and would
require further extending generic BTF writer APIs. So that is left for future
follow ups, if there will be demand for that. But the idea seems intresting
and useful, so I want to document it here.
Weak definitions are also supported, but are pretty strict as well, just
like externs: all weak map definitions have to match exactly. In the follow up
patches this most probably will be relaxed, with __weak map definitions being
able to differ between each other (with non-weak definition always winning, of
course).
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/20210423181348.1801389-13-andrii@kernel.org
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
Make skip_mods_and_typedefs(), btf_kind_str(), and btf_func_linkage() helpers
available outside of libbpf.c, to be used by static linker code.
Also do few cleanups (error code fixes, comment clean up, etc) that don't
deserve their own commit.
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/20210423181348.1801389-9-andrii@kernel.org
Factor out logic for sanity checking SHT_SYMTAB and SHT_REL sections into
separate sections. They are already quite extensive and are suffering from too
deep indentation. Subsequent changes will extend SYMTAB sanity checking
further, so it's better to factor each into a separate function.
No functional changes are intended.
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/20210423181348.1801389-8-andrii@kernel.org
Refactor BTF-defined maps parsing logic to allow it to be nicely reused by BPF
static linker. Further, at least for BPF static linker, it's important to know
which attributes of a BPF map were defined explicitly, so provide a bit set
for each known portion of BTF map definition. This allows BPF static linker to
do a simple check when dealing with extern map declarations.
The same capabilities allow to distinguish attributes explicitly set to zero
(e.g., __uint(max_entries, 0)) vs the case of not specifying it at all (no
max_entries attribute at all). Libbpf is currently not utilizing that, but it
could be useful for backwards compatibility reasons later.
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/20210423181348.1801389-7-andrii@kernel.org
Currently libbpf is very strict about parsing BPF program instruction
sections. No gaps are allowed between sequential BPF programs within a given
ELF section. Libbpf enforced that by keeping track of the next section offset
that should start a new BPF (sub)program and cross-checks that by searching
for a corresponding STT_FUNC ELF symbol.
But this is too restrictive once we allow to have weak BPF programs and link
together two or more BPF object files. In such case, some weak BPF programs
might be "overridden" by either non-weak BPF program with the same name and
signature, or even by another weak BPF program that just happened to be linked
first. That, in turn, leaves BPF instructions of the "lost" BPF (sub)program
intact, but there is no corresponding ELF symbol, because no one is going to
be referencing it.
Libbpf already correctly handles such cases in the sense that it won't append
such dead code to actual BPF programs loaded into kernel. So the only change
that needs to be done is to relax the logic of parsing BPF instruction
sections. Instead of assuming next BPF (sub)program section offset, iterate
available STT_FUNC ELF symbols to discover all available BPF subprograms and
programs.
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/20210423181348.1801389-6-andrii@kernel.org
Define __hidden helper macro in bpf_helpers.h, which is a short-hand for
__attribute__((visibility("hidden"))). Add libbpf support to mark BPF
subprograms marked with __hidden as static in BTF information to enforce BPF
verifier's static function validation algorithm, which takes more information
(caller's context) into account during a subprogram validation.
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/20210423181348.1801389-5-andrii@kernel.org
Ensure that BPF static linker preserves all DATASEC BTF types, even if some of
them might not have any variable information at all. This may happen if the
compiler promotes local initialized variable contents into .rodata section and
there are no global or static functions in the program.
For example,
$ cat t.c
struct t { char a; char b; char c; };
void bar(struct t*);
void find() {
struct t tmp = {1, 2, 3};
bar(&tmp);
}
$ clang -target bpf -O2 -g -S t.c
.long 104 # BTF_KIND_DATASEC(id = 8)
.long 251658240 # 0xf000000
.long 0
.ascii ".rodata" # string offset=104
$ clang -target bpf -O2 -g -c t.c
$ readelf -S t.o | grep data
[ 4] .rodata PROGBITS 0000000000000000 00000090
Fixes: 8fd27bf69b86 ("libbpf: Add BPF static linker BTF and BTF.ext support")
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210326043036.3081011-1-andrii@kernel.org
Update links to point to blog posts that have some new updates and are
generally kept more up-to-date.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
libbpf_util.h was removed in 7e8bbe24cb8b ("libbpf: xsk: Move barriers from
libbpf_util.h to xsk.h") upstream, so remove it from the list of installable
headers.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Add .BTF and .BTF.ext static linking logic.
When multiple BPF object files are linked together, their respective .BTF and
.BTF.ext sections are merged together. BTF types are not just concatenated,
but also deduplicated. .BTF.ext data is grouped by type (func info, line info,
core_relos) and target section names, and then all the records are
concatenated together, preserving their relative order. All the BTF type ID
references and string offsets are updated as necessary, to take into account
possibly deduplicated strings and types.
BTF DATASEC types are handled specially. Their respective var_secinfos are
accumulated separately in special per-section data and then final DATASEC
types are emitted at the very end during bpf_linker__finalize() operation,
just before emitting final ELF output file.
BTF data can also provide "section annotations" for some extern variables.
Such concept is missing in ELF, but BTF will have DATASEC types for such
special extern datasections (e.g., .kconfig, .ksyms). Such sections are called
"ephemeral" internally. Internally linker will keep metadata for each such
section, collecting variables information, but those sections won't be emitted
into the final ELF file.
Also, given LLVM/Clang during compilation emits BTF DATASECS that are
incomplete, missing section size and variable offsets for static variables,
BPF static linker will initially fix up such DATASECs, using ELF symbols data.
The final DATASECs will preserve section sizes and all variable offsets. This
is handled correctly by libbpf already, so won't cause any new issues. On the
other hand, it's actually a nice property to have a complete BTF data without
runtime adjustments done during bpf_object__open() by libbpf. In that sense,
BPF static linker is also a BTF normalizer.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210318194036.3521577-8-andrii@kernel.org
Introduce BPF static linker APIs to libbpf. BPF static linker allows to
perform static linking of multiple BPF object files into a single combined
resulting object file, preserving all the BPF programs, maps, global
variables, etc.
Data sections (.bss, .data, .rodata, .maps, maps, etc) with the same name are
concatenated together. Similarly, code sections are also concatenated. All the
symbols and ELF relocations are also concatenated in their respective ELF
sections and are adjusted accordingly to the new object file layout.
Static variables and functions are handled correctly as well, adjusting BPF
instructions offsets to reflect new variable/function offset within the
combined ELF section. Such relocations are referencing STT_SECTION symbols and
that stays intact.
Data sections in different files can have different alignment requirements, so
that is taken care of as well, adjusting sizes and offsets as necessary to
satisfy both old and new alignment requirements.
DWARF data sections are stripped out, currently. As well as LLLVM_ADDRSIG
section, which is ignored by libbpf in bpf_object__open() anyways. So, in
a way, BPF static linker is an analogue to `llvm-strip -g`, which is a pretty
nice property, especially if resulting .o file is then used to generate BPF
skeleton.
Original string sections are ignored and instead we construct our own set of
unique strings using libbpf-internal `struct strset` API.
To reduce the size of the patch, all the .BTF and .BTF.ext processing was
moved into a separate patch.
The high-level API consists of just 4 functions:
- bpf_linker__new() creates an instance of BPF static linker. It accepts
output filename and (currently empty) options struct;
- bpf_linker__add_file() takes input filename and appends it to the already
processed ELF data; it can be called multiple times, one for each BPF
ELF object file that needs to be linked in;
- bpf_linker__finalize() needs to be called to dump final ELF contents into
the output file, specified when bpf_linker was created; after
bpf_linker__finalize() is called, no more bpf_linker__add_file() and
bpf_linker__finalize() calls are allowed, they will return error;
- regardless of whether bpf_linker__finalize() was called or not,
bpf_linker__free() will free up all the used resources.
Currently, BPF static linker doesn't resolve cross-object file references
(extern variables and/or functions). This will be added in the follow up patch
set.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210318194036.3521577-7-andrii@kernel.org
Add btf__add_type() API that performs shallow copy of a given BTF type from
the source BTF into the destination BTF. All the information and type IDs are
preserved, but all the strings encountered are added into the destination BTF
and corresponding offsets are rewritten. BTF type IDs are assumed to be
correct or such that will be (somehow) modified afterwards.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210318194036.3521577-6-andrii@kernel.org
Extract BTF logic for maintaining a set of strings data structure, used for
BTF strings section construction in writable mode, into separate re-usable
API. This data structure is going to be used by bpf_linker to maintains ELF
STRTAB section, which has the same layout as BTF strings section.
Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210318194036.3521577-5-andrii@kernel.org
Extract and generalize the logic to iterate BTF type ID and string offset
fields within BTF types and .BTF.ext data. Expose this internally in libbpf
for re-use by bpf_linker.
Additionally, complete strings deduplication handling for BTF.ext (e.g., CO-RE
access strings), which was previously missing. There previously was no
case of deduplicating .BTF.ext data, but bpf_linker is going to use it.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210318194036.3521577-3-andrii@kernel.org
Andrii Nakryiko