Loading BTF and BTF.ext from ELF file is a common need. Instead of
requiring every user to re-implement it, let's provide this API from
libbpf itself. It's mostly copy/paste from `bpftool btf dump`
implementation, which will be switched to libbpf's version in next
patch. btf__parse_elf allows to load BTF and optionally BTF.ext.
This is also useful for tests that need to load/work with BTF, loaded
from test ELF files.
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

libbpf_util.h header was recently exposed as public as a dependency of
xsk.h. In addition to memory barriers, it contained logging helpers,
which are not supposed to be exposed. This patch moves those into
libbpf_internal.h, which is kept as an internal header.

Cc: Stanislav Fomichev <sdf@google.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Fixes: 7080da89 ("libbpf: add libbpf_util.h to header install.")
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

This patch adds support for VAR and DATASEC in btf_dedup(). VAR/DATASEC
are never deduplicated, but they need to be processed anyway as types
they refer to might need to be remapped due to deduplication and
compaction.

Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Yonghong Song <yhs@fb.com>
Cc: Alexei Starovoitov <ast@fb.com>
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

This adds libbpf support for BTF Var and DataSec kinds. Main point
here is that libbpf needs to do some preparatory work before the
whole BTF object can be loaded into the kernel, that is, fixing up
of DataSec size taken from the ELF section size and non-static
variable offset which needs to be taken from the ELF's string section.

Upstream LLVM doesn't fix these up since at time of BTF emission
it is too early in the compilation process thus this information
isn't available yet, hence loader needs to take care of it.

Note, deduplication handling has not been in the scope of this work
and needs to be addressed in a future commit.
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Link: https://reviews.llvm.org/D59441Acked-by: NMartin KaFai Lau <kafai@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

btf_dedup_is_equiv() used to compare btf_type->info fields, before doing
kind-specific equivalence check. This comparsion implicitly verified
that candidate and canonical types are of the same kind. With enum fwd
resolution logic this check couldn't be done generically anymore, as for
enums info contains vlen, which differs between enum fwd and
fully-defined enum, so this check was subsumed by kind-specific
equivalence checks.

This change caused btf_dedup_is_equiv() to let through VOID vs other
types check to reach switch, which was never meant to be handing VOID
kind, as VOID kind is always pre-resolved to itself and is only
equivalent to itself, which is checked early in btf_dedup_is_equiv().

This change adds back BTF kind equality check in place of more generic
btf_type->info check, still defering further kind-specific checks to
a per-kind switch.

Fixes: 9768095b ("btf: resolve enum fwds in btf_dedup")
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

GCC and clang support enum forward declarations as an extension. Such
forward-declared enums will be represented as normal BTF_KIND_ENUM types with
vlen=0. This patch adds ability to resolve such enums to their corresponding
fully defined enums. This helps to avoid duplicated BTF type graphs which only
differ by some types referencing forward-declared enum vs full enum.

One such example in kernel is enum irqchip_irq_state, defined in
include/linux/interrupt.h and forward-declared in include/linux/irq.h. This
causes entire struct task_struct and all referenced types to be duplicated in
btf_dedup output. This patch eliminates such duplication cases.
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

When checking available canonical candidates for struct/union algorithm
utilizes btf_dedup_is_equiv to determine if candidate is suitable. This
check is not enough when candidate is corresponding FWD for that
struct/union, because according to equivalence logic they are
equivalent. When it so happens that FWD and STRUCT/UNION end in hashing
to the same bucket, it's possible to create remapping loop from FWD to
STRUCT and STRUCT to same FWD, which will cause btf_dedup() to loop
forever.

This patch fixes the issue by additionally checking that type and
canonical candidate are strictly equal (utilizing btf_equal_struct).

Fixes: d5caef5b ("btf: add BTF types deduplication algorithm")
Reported-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Acked-by: NSong Liu <songliubraving@fb.com>
Acked-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

Default size of dedup table (16k) is good enough for most binaries, even
typical vmlinux images. But there are cases of binaries with huge amount
of BTF types (e.g., allyesconfig variants of kernel), which benefit from
having bigger dedup table size to lower amount of unnecessary hash
collisions. Tools like pahole, thus, can tune this parameter to reach
optimal performance.

This change also serves double purpose of allowing tests to force hash
collisions to test some corner cases, used in follow up patch.
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Acked-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

The "ref_type_id" variable needs to be signed for the error handling
to work.

Fixes: d5caef5b ("btf: add BTF types deduplication algorithm")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Acked-by: NAndrii Nakryiko <andriin@fb.com>
Acked-by: NSong Liu <songliubraving@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

While it's understandable why kernel limits number of BTF types to 65535
and size of string section to 64KB, in libbpf as user-space library it's
too restrictive. E.g., pahole converting DWARF to BTF type information
for Linux kernel generates more than 3 million BTF types and more than
3MB of strings, before deduplication. So to allow btf__dedup() to do its
work, we need to be able to load bigger BTF sections using btf__new().
Singed-off-by: NAndrii Nakryiko <andriin@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

bzero() call is deprecated and superseded by memset().
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Reported-by: NDavid Laight <david.laight@aculab.com>
Acked-by: NMartin KaFai Lau <kafai@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

Now that we have btf__get_raw_data() it's trivial for tests to iterate
over all strings for testing purposes, which eliminates the need for
btf__get_strings() API.
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Acked-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

This patch changes struct btf_ext to retain original data in sequential
block of memory, which makes it possible to expose
btf_ext__get_raw_data() interface similar to btf__get_raw_data(), allowing
users of libbpf to get access to raw representation of .BTF.ext section.
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Acked-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

This patch exposes new API btf__get_raw_data() that allows to get a copy
of raw BTF data out of struct btf. This is useful for external programs
that need to manipulate raw data, e.g., pahole using btf__dedup() to
deduplicate BTF type info and then writing it back to file.
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Acked-by: NSong Liu <songliubraving@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

This change splits out previous btf__new functionality of constructing
struct btf and loading it into kernel into two:
- btf__new() just creates and initializes struct btf
- btf__load() attempts to load existing struct btf into kernel

btf__free will still close BTF fd, if it was ever loaded successfully
into kernel.

This change allows users of libbpf to manipulate BTF using its API,
without the need to unnecessarily load it into kernel.

One of the intended use cases is pahole, which will do DWARF to BTF
conversion and then use libbpf to do type deduplication, while then
handling ELF sections overwriting and other concerns on its own.

Fixes: 2d3feca8 ("bpf: btf: print map dump and lookup with btf info")
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Acked-by: NSong Liu <songliubraving@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

Few files in libbpf are using bzero() function (defined in strings.h header), but
don't include corresponding header. When libbpf is added as a dependency to pahole,
this undeterministically causes warnings on some machines:

bpf.c:225:2: warning: implicit declaration of function 'bzero' [-Wimplicit-function-declaration]
  bzero(&attr, sizeof(attr));
    ^~~~~
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Reported-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

Commit 96408c43 ("tools/bpf: implement libbpf
btf__get_map_kv_tids() API function") refactored
function bpf_map_find_btf_info() and moved bulk of
implementation into btf.c as btf__get_map_kv_tids().
This change introduced a bug such that test_btf will
print out the following warning although the test passed:
  BTF libbpf test[2] (test_btf_nokv.o): libbpf: map:btf_map
      container_name:____btf_map_btf_map cannot be found
      in BTF. Missing BPF_ANNOTATE_KV_PAIR?

Previously, the error message is guarded with pr_debug().
Commit 96408c43 changed it to pr_warning() and
hence caused the warning.

Restoring to pr_debug() for the message fixed the issue.

Fixes: 96408c43 ("tools/bpf: implement libbpf btf__get_map_kv_tids() API function")
Signed-off-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

Commit 96408c43 ("tools/bpf: implement libbpf btf__get_map_kv_tids() API function")
added the API function btf__get_map_kv_tids():
  btf__get_map_kv_tids(const struct btf *btf, char *map_name, ...)

The parameter map_name has type "char *". This is okay inside libbpf library since
the map_name is from bpf_map->name which also has type "char *".

This will be problematic if the caller for map_name already has attribute "const",
e.g., from C++ string.c_str(). It will result in either a warning or an error.

  /home/yhs/work/bcc/src/cc/btf.cc:166:51:
    error: invalid conversion from ‘const char*’ to ‘char*’ [-fpermissive]
      return btf__get_map_kv_tids(btf_, map_name.c_str()

This patch added "const" attributes to map_name parameter.

Fixes: 96408c43 ("tools/bpf: implement libbpf btf__get_map_kv_tids() API function")
Signed-off-by: NYonghong Song <yhs@fb.com>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

This patch sets up a new kind of tests (BTF dedup tests) and tests few aspects of
BTF dedup algorithm. More complete set of tests will come in follow up patches.
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

This patch implements BTF types deduplication algorithm. It allows to
greatly compress typical output of pahole's DWARF-to-BTF conversion or
LLVM's compilation output by detecting and collapsing identical types emitted in
isolation per compilation unit. Algorithm also resolves struct/union forward
declarations into concrete BTF types representing referenced struct/union. If
undesired, this resolution can be disabled through specifying corresponding options.

Algorithm itself and its application to Linux kernel's BTF types is
described in details at:
https://facebookmicrosites.github.io/bpf/blog/2018/11/14/btf-enhancement.htmlSigned-off-by: NAndrii Nakryiko <andriin@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

This pre-patch extracts calculation of amount of space taken by BTF type descriptor
for later reuse by btf_dedup functionality.
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

Currently, to get map key/value type id's, the macro
  BPF_ANNOTATE_KV_PAIR(<map_name>, <key_type>, <value_type>)
needs to be defined in the bpf program for the
corresponding map.

During program/map loading time,
the local static function bpf_map_find_btf_info()
in libbpf.c is implemented to retrieve the key/value
type ids given the map name.

The patch refactored function bpf_map_find_btf_info()
to create an API btf__get_map_kv_tids() which includes
the bulk of implementation for the original function.
The API btf__get_map_kv_tids() can be used by bcc,
a JIT based bpf compilation system, which uses the
same BPF_ANNOTATE_KV_PAIR to record map key/value types.
Acked-by: NMartin KaFai Lau <kafai@fb.com>
Signed-off-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

Currently, the btf log is allocated and printed out in case
of error at LIBBPF_DEBUG level.
Such logs from kernel are very important for debugging.
For example, bpf syscall BPF_PROG_LOAD command can get
verifier logs back to user space. In function load_program()
of libbpf.c, the log buffer is allocated unconditionally
and printed out at pr_warning() level.

Let us do the similar thing here for btf. Allocate buffer
unconditionally and print out error logs at pr_warning() level.
This can reduce one global function and
optimize for common situations where pr_warning()
is activated either by default or by user supplied
debug output function.
Signed-off-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

A global function libbpf_print, which is invisible
outside the shared library, is defined to print based
on levels. The pr_warning, pr_info and pr_debug
macros are moved into the newly created header
common.h. So any .c file including common.h can
use these macros directly.

Currently btf__new and btf_ext__new API has an argument getting
__pr_debug function pointer into btf.c so the debugging information
can be printed there. This patch removed this parameter
from btf__new and btf_ext__new and directly using pr_debug in btf.c.

Another global function libbpf_print_level_available, also
invisible outside the shared library, can test
whether a particular level debug printing is
available or not. It is used in btf.c to
test whether DEBUG level debug printing is availabl or not,
based on which the log buffer will be allocated when loading
btf to the kernel.
Signed-off-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

This patch adds bpf_line_info support to libbpf:
1) Parsing the line_info sec from ".BTF.ext"
2) Relocating the line_info.  If the main prog *_info relocation
   fails, it will ignore the remaining subprog line_info and continue.
   If the subprog *_info relocation fails, it will bail out.
3) BPF_PROG_LOAD a prog with line_info
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Acked-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

This patch refactor and fix a bug in the libbpf's bpf_func_info loading
logic.  The bug fix and refactoring are targeting the same
commit 2993e051 ("tools/bpf: add support to read .BTF.ext sections")
which is in the bpf-next branch.

1) In bpf_load_program_xattr(), it should retry when errno == E2BIG
   regardless of log_buf and log_buf_sz.  This patch fixes it.

2) btf_ext__reloc_init() and btf_ext__reloc() are essentially
   the same except btf_ext__reloc_init() always has insns_cnt == 0.
   Hence, btf_ext__reloc_init() is removed.

   btf_ext__reloc() is also renamed to btf_ext__reloc_func_info()
   to get ready for the line_info support in the next patch.

3) Consolidate func_info section logic from "btf_ext_parse_hdr()",
   "btf_ext_validate_func_info()" and "btf_ext__new()" to
   a new function "btf_ext_copy_func_info()" such that similar
   logic can be reused by the later libbpf's line_info patch.

4) The next line_info patch will store line_info_cnt instead of
   line_info_len in the bpf_program because the kernel is taking
   line_info_cnt also.  It will save a few "len" to "cnt" conversions
   and will also save some function args.

   Hence, this patch also makes bpf_program to store func_info_cnt
   instead of func_info_len.

5) btf_ext depends on btf.  e.g. the func_info's type_id
   in ".BTF.ext" is not useful when ".BTF" is absent.
   This patch only init the obj->btf_ext pointer after
   it has successfully init the obj->btf pointer.

   This can avoid always checking "obj->btf && obj->btf_ext"
   together for accessing ".BTF.ext".  Checking "obj->btf_ext"
   alone will do.

6) Move "struct btf_sec_func_info" from btf.h to btf.c.
   There is no external usage outside btf.c.

Fixes: 2993e051 ("tools/bpf: add support to read .BTF.ext sections")
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Acked-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

Similar to info.jited_*, info.func_info could be 0 if
bpf_dump_raw_ok() == false.

This patch makes changes to test_btf and bpftool to expect info.func_info
could be 0.

This patch also makes the needed changes for s/insn_offset/insn_off/.
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Acked-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

Cannot cast a u64 to a pointer on 32-bit without an intervening (long)
cast otherwise GCC warns.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Acked-by: NSong Liu <songliubraving@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

s/btf_get_from_id/btf__get_from_id/ to restore the API naming convention.
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Signed-off-by: NAndrey Ignatov <rdna@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

The function get_btf() is implemented in tools/bpf/bpftool/map.c
to get a btf structure given a map_info. This patch
refactored this function to be function btf_get_from_id()
in tools/lib/bpf so that it can be used later.
Signed-off-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

The .BTF section is already available to encode types.
These types can be used for map
pretty print. The whole .BTF will be passed to the
kernel as well for which kernel can verify and return
to the user space for pretty print etc.

The llvm patch at https://reviews.llvm.org/D53736
will generate .BTF section and one more section .BTF.ext.
The .BTF.ext section encodes function type
information and line information. Note that
this patch set only supports function type info.
The functionality is implemented in libbpf.

The .BTF section can be directly loaded into the
kernel, and the .BTF.ext section cannot. The loader
may need to do some relocation and merging,
similar to merging multiple code sections, before
loading into the kernel.
Signed-off-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

This patch adds unit tests for BTF_KIND_FUNC_PROTO and
BTF_KIND_FUNC to test_btf.
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Signed-off-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

libbpf is maturing as a library and gaining features that no other bpf libraries support
(BPF Type Format, bpf to bpf calls, etc)
Many Apache2 licensed projects (like bcc, bpftrace, gobpf, cilium, etc)
would like to use libbpf, but cannot do this yet, since Apache Foundation explicitly
states that LGPL is incompatible with Apache2.
Hence let's relicense libbpf as dual license LGPL-2.1 or BSD-2-Clause,
since BSD-2 is compatible with Apache2.
Dual LGPL or Apache2 is invalid combination.
Fix license mistake in Makefile as well.
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NAndrey Ignatov <rdna@fb.com>
Acked-by: NArnaldo Carvalho de Melo <acme@kernel.org>
Acked-by: NBjörn Töpel <bjorn.topel@intel.com>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NDavid Beckett <david.beckett@netronome.com>
Acked-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: NJoe Stringer <joe@ovn.org>
Acked-by: NJohn Fastabend <john.fastabend@gmail.com>
Acked-by: NMartin KaFai Lau <kafai@fb.com>
Acked-by: NQuentin Monnet <quentin.monnet@netronome.com>
Acked-by: NThomas Graf <tgraf@suug.ch>
Acked-by: NRoman Gushchin <guro@fb.com>
Acked-by: NWang Nan <wangnan0@huawei.com>
Acked-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

This patch changes the tools/lib/bpf/btf.[ch] to LGPL which
is inline with libbpf also.
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

commit 38d5d3b3 ("bpf: Introduce BPF_ANNOTATE_KV_PAIR")

added to the bpf and net trees what

commit 92b57121 ("bpf: btf: export btf types and name by offset from lib")

has already added to bpf-next/net-next, but in slightly different
location.  Remove the duplicates (to fix build of libbpf).
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This patch introduces BPF_ANNOTATE_KV_PAIR to signal the
bpf loader about the btf key_type and value_type of a bpf map.
Please refer to the changes in test_btf_haskv.c for its usage.
Both iproute2 and libbpf loader will then have the same
convention to find out the map's btf_key_type_id and
btf_value_type_id from a map's name.

Fixes: 8a138aed ("bpf: btf: Add BTF support to libbpf")
Suggested-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Acked-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

This patch replaces [u]int32_t and [u]int64_t usage with
__[su]32 and __[su]64.  The same change goes for [u]int16_t
and [u]int8_t.

Fixes: 8a138aed ("bpf: btf: Add BTF support to libbpf")
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Acked-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

This patch introduces btf__resolve_type() function and exports two
existing functions from libbpf. btf__resolve_type follows modifier
types like const and typedef until it hits a type which actually takes
up memory, and then returns it. This function follows similar pattern
to btf__resolve_size but instead of computing size, it just returns
the type.

These  functions will be used in the followig patch which parses
information inside array of `struct btf_type *`. btf_name_by_offset is
used for printing variable names.
Signed-off-by: NOkash Khawaja <osk@fb.com>
Acked-by: NMartin KaFai Lau <kafai@fb.com>
Acked-by: NSong Liu <songliubraving@fb.com>
Reviewed-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

This patch does the followings:
1. Modify libbpf and test_btf to reflect the uapi changes in btf
2. Add test for the btf_header changes
3. Add tests for array->index_type
4. Add err_str check to the tests
5. Fix a 4 bytes hole in "struct test #1" by swapping "m" and "n"
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

This patch cleans up btf.h in uapi:
1) Rename "name" to "name_off" to better reflect it is an offset to the
   string section instead of a char array.
2) Remove unused value BTF_FLAGS_COMPR and BTF_MAGIC_SWAP
Suggested-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>