libbpf: add non-mmapable data section selftest

Add non-mmapable data section to test_skeleton selftest and make sure it
really isn't mmapable by trying to mmap() it anyways.

Also make sure that libbpf doesn't report BPF_F_MMAPABLE flag to users.

Additional, some more manual testing was performed that this feature
works as intended.

Looking at created map through bpftool shows that flags passed to kernel are
indeed zero:

$ bpftool map show
...
1782: array name .data.non_mmapa flags 0x0
key 4B value 16B max_entries 1 memlock 4096B
btf_id 1169
pids test_progs(8311)
...

Checking BTF uploaded to kernel for this map shows that zero_key and
zero_value are indeed marked as static, even though zero_key is actually
original global (but STV_HIDDEN) variable:

$ bpftool btf dump id 1169
...
[51] VAR 'zero_key' type_id=2, linkage=static
[52] VAR 'zero_value' type_id=7, linkage=static
...
[62] DATASEC '.data.non_mmapable' size=16 vlen=2
type_id=51 offset=0 size=4 (VAR 'zero_key')
type_id=52 offset=4 size=12 (VAR 'zero_value')
...

And original BTF does have zero_key marked as linkage=global:

$ bpftool btf dump file test_skeleton.bpf.linked3.o
...
[51] VAR 'zero_key' type_id=2, linkage=global
[52] VAR 'zero_value' type_id=7, linkage=static
...
[62] DATASEC '.data.non_mmapable' size=16 vlen=2
type_id=51 offset=0 size=4 (VAR 'zero_key')
type_id=52 offset=4 size=12 (VAR 'zero_value')

Bpftool didn't require any changes at all because it checks whether internal
map is mmapable already, but just to double-check generated skeleton, we
see that .data.non_mmapable neither sets mmaped pointer nor has
a corresponding field in the skeleton:

$ grep non_mmapable test_skeleton.skel.h
struct bpf_map *data_non_mmapable;
s->maps[7].name = ".data.non_mmapable";
s->maps[7].map = &obj->maps.data_non_mmapable;

But .data.read_mostly has all of those things:

$ grep read_mostly test_skeleton.skel.h
struct bpf_map *data_read_mostly;
struct test_skeleton__data_read_mostly {
int read_mostly_var;
} *data_read_mostly;
s->maps[6].name = ".data.read_mostly";
s->maps[6].map = &obj->maps.data_read_mostly;
s->maps[6].mmaped = (void **)&obj->data_read_mostly;
_Static_assert(sizeof(s->data_read_mostly->read_mostly_var) == 4, "unexpected size of 'read_mostly_var'");

Acked-by: Stanislav Fomichev <sdf@google.com>
Acked-by: Dave Marchevsky <davemarchevsky@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20221019002816.359650-4-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

selftests/bpf: validate .bss section bigger than 8MB is possible now

Add a simple big 16MB array and validate access to the very last byte of
it to make sure that kernel supports > KMALLOC_MAX_SIZE value_size for
BPF array maps (which are backing .bss in this case).

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20220715053146.1291891-5-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

selftests/bpf: Demonstrate use of custom .rodata/.data sections

Enhance existing selftests to demonstrate the use of custom
.data/.rodata sections.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20211021014404.2635234-9-andrii@kernel.org

selftests/bpf: Stop using static variables for passing data to/from user-space

In preparation of skipping emitting static variables in BPF skeletons, switch
all current selftests uses of static variables to pass data between BPF and
user-space to use global variables.

All non-read-only `static volatile` variables become just plain global
variables by dropping `static volatile` part.

Read-only `static volatile const` variables, though, still require `volatile`
modifier, otherwise compiler will ignore whatever values are set from
user-space.

Few static linker tests are using name-conflicting static variables to
validate that static linker still properly handles static variables and
doesn't trip up on name conflicts.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210507054119.270888-4-andrii@kernel.org

tools/bpftool: Strip away modifiers from global variables

Reliably remove all the type modifiers from read-only (.rodata) global
variable definitions, including cases of inner field const modifiers and
arrays of const values.

Also modify one of selftests to ensure that const volatile struct doesn't
prevent user-space from modifying .rodata variable.

Fixes: 985ead416df3 ("bpftool: Add skeleton codegen command")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200713232409.3062144-3-andriin@fb.com

libbpf: Support pre-initializing .bss global variables

Remove invalid assumption in libbpf that .bss map doesn't have to be updated
in kernel. With addition of skeleton and memory-mapped initialization image,
.bss doesn't have to be all zeroes when BPF map is created, because user-code
might have initialized those variables from user-space.

Fixes: eba9c5f498a1 ("libbpf: Refactor global data map initialization")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200612194504.557844-1-andriin@fb.com

selftests: Use consistent include paths for libbpf

Fix all selftests to include libbpf header files with the bpf/ prefix, to
be consistent with external users of the library. Also ensure that all
includes of exported libbpf header files (those that are exported on 'make
install' of the library) use bracketed includes instead of quoted.

To not break the build, keep the old include path until everything has been
changed to the new one; a subsequent patch will remove that.

Fixes: 6910d7d3867a ("selftests/bpf: Ensure bpf_helper_defs.h are taken from selftests dir")
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/157952560568.1683545.9649335788846513446.stgit@toke.dk

libbpf: Put Kconfig externs into .kconfig section

Move Kconfig-provided externs into custom .kconfig section. Add __kconfig into
bpf_helpers.h for user convenience. Update selftests accordingly.

Suggested-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191219002837.3074619-2-andriin@fb.com

selftests/bpf: Add tests for libbpf-provided externs

Add a set of tests validating libbpf-provided extern variables. One crucial
feature that's tested is dead code elimination together with using invalid BPF
helper. CONFIG_MISSING is not supposed to exist and should always be specified
by libbpf as zero, which allows BPF verifier to correctly do branch pruning
and not fail validation, when invalid BPF helper is called from dead if branch.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191214014710.3449601-5-andriin@fb.com

selftests/bpf: Add test validating data section to struct convertion layout

Add a simple selftests validating datasection-to-struct layour dumping. Global
variables are constructed in such a way as to cause both natural and
artificial padding (through custom alignment requirement).

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20191214014341.3442258-17-andriin@fb.com