linux.git/tools/lib/bpf/libbpf.c, branch v5.13

libbpf: Add NULL check to add_dummy_ksym_var

2021-05-05T18:29:33+00:00

Avoids a segv if btf isn't present. Seen on the call path
__bpf_object__open calling bpf_object__collect_externs.

Fixes: 5bd022ec01f0 (libbpf: Support extern kernel function)
Suggested-by: Stanislav Fomichev 
Suggested-by: Petar Penkov 
Signed-off-by: Ian Rogers 
Signed-off-by: Andrii Nakryiko 
Link: https://lore.kernel.org/bpf/20210504234910.976501-1-irogers@google.com

libbpf: Support BTF_KIND_FLOAT during type compatibility checks in CO-RE

2021-04-27T01:37:13+00:00

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 
Signed-off-by: Alexei Starovoitov 
Acked-by: Lorenz Bauer 
Link: https://lore.kernel.org/bpf/20210426192949.416837-3-andrii@kernel.org

libbpf: Make few internal helpers available outside of libbpf.c

2021-04-23T21:05:26+00:00

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 
Signed-off-by: Alexei Starovoitov 
Acked-by: Yonghong Song 
Link: https://lore.kernel.org/bpf/20210423181348.1801389-9-andrii@kernel.org

libbpf: Refactor BTF map definition parsing

2021-04-23T21:05:26+00:00

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 
Signed-off-by: Alexei Starovoitov 
Acked-by: Yonghong Song 
Link: https://lore.kernel.org/bpf/20210423181348.1801389-7-andrii@kernel.org

libbpf: Allow gaps in BPF program sections to support overriden weak functions

2021-04-23T21:05:26+00:00

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 
Signed-off-by: Alexei Starovoitov 
Acked-by: Yonghong Song 
Link: https://lore.kernel.org/bpf/20210423181348.1801389-6-andrii@kernel.org

libbpf: Mark BPF subprogs with hidden visibility as static for BPF verifier

2021-04-23T21:05:26+00:00

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 
Signed-off-by: Alexei Starovoitov 
Acked-by: Yonghong Song 
Link: https://lore.kernel.org/bpf/20210423181348.1801389-5-andrii@kernel.org

libbpf: Remove unused field.

2021-04-15T22:34:16+00:00

relo->processed is set, but not used. Remove it.

Signed-off-by: Alexei Starovoitov 
Signed-off-by: Andrii Nakryiko 
Link: https://lore.kernel.org/bpf/20210415141817.53136-1-alexei.starovoitov@gmail.com

libbpf: Add bpf_map__inner_map API

2021-04-09T06:54:48+00:00

The API gives access to inner map for map in map types (array or
hash of map). It will be used to dynamically set max_entries in it.

Signed-off-by: Yauheni Kaliuta 
Signed-off-by: Andrii Nakryiko 
Link: https://lore.kernel.org/bpf/20210408061310.95877-7-yauheni.kaliuta@redhat.com

libbpf: Support extern kernel function

2021-03-27T03:41:51+00:00

This patch is to make libbpf able to handle the following extern
kernel function declaration and do the needed relocations before
loading the bpf program to the kernel.

extern int foo(struct sock *) __attribute__((section(".ksyms")))

In the collect extern phase, needed changes is made to
bpf_object__collect_externs() and find_extern_btf_id() to collect
extern function in ".ksyms" section.  The func in the BTF datasec also
needs to be replaced by an int var.  The idea is similar to the existing
handling in extern var.  In case the BTF may not have a var, a dummy ksym
var is added at the beginning of bpf_object__collect_externs()
if there is func under ksyms datasec.  It will also change the
func linkage from extern to global which the kernel can support.
It also assigns a param name if it does not have one.

In the collect relo phase, it will record the kernel function
call as RELO_EXTERN_FUNC.

bpf_object__resolve_ksym_func_btf_id() is added to find the func
btf_id of the running kernel.

During actual relocation, it will patch the BPF_CALL instruction with
src_reg = BPF_PSEUDO_FUNC_CALL and insn->imm set to the running
kernel func's btf_id.

The required LLVM patch: https://reviews.llvm.org/D93563

Signed-off-by: Martin KaFai Lau 
Signed-off-by: Alexei Starovoitov 
Link: https://lore.kernel.org/bpf/20210325015234.1548923-1-kafai@fb.com

libbpf: Record extern sym relocation first

2021-03-27T03:41:51+00:00

This patch records the extern sym relocs first before recording
subprog relocs.  The later patch will have relocs for extern
kernel function call which is also using BPF_JMP | BPF_CALL.
It will be easier to handle the extern symbols first in
the later patch.

is_call_insn() helper is added.  The existing is_ldimm64() helper
is renamed to is_ldimm64_insn() for consistency.

Signed-off-by: Martin KaFai Lau 
Signed-off-by: Alexei Starovoitov 
Acked-by: Andrii Nakryiko 
Link: https://lore.kernel.org/bpf/20210325015227.1548623-1-kafai@fb.com