Andrii Nakryiko says:

====================
Add support for loading and storing BTF in either little- or big-endian
integer encodings, regardless of host endianness. This allows users of libbpf
to not care about endianness when they don't want to and transparently
open/load BTF of any endianness. libbpf will preserve original endianness and
will convert output raw data as necessary back to original endianness, if
necessary. This allows tools like pahole to be ignorant to such issues during
cross-compilation.

While working with BTF data in memory, the endianness is always native to the
host. Convetion can happen only during btf__get_raw_data() call, and only in
a raw data copy.

Additionally, it's possible to force output BTF endianness through new
btf__set_endianness() API. This which allows to create flexible tools doing
arbitrary conversions of BTF endianness, just by relying on libbpf.

Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Cc: Tony Ambardar <tony.ambardar@gmail.com>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Luka Perkov <luka.perkov@sartura.hr>
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Add selftests juggling endianness back and forth to validate BTF's handling of
endianness convertions internally.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200929043046.1324350-4-andriin@fb.com

Teach BTF to recognized wrong endianness and transparently convert it
internally to host endianness. Original endianness of BTF will be preserved
and used during btf__get_raw_data() to convert resulting raw data to the same
endianness and a source raw_data. This means that little-endian host can parse
big-endian BTF with no issues, all the type data will be presented to the
client application in native endianness, but when it's time for emitting BTF
to persist it in a file (e.g., after BTF deduplication), original non-native
endianness will be preserved and stored.

It's possible to query original endianness of BTF data with new
btf__endianness() API. It's also possible to override desired output
endianness with btf__set_endianness(), so that if application needs to load,
say, big-endian BTF and store it as little-endian BTF, it's possible to
manually override this. If btf__set_endianness() was used to change
endianness, btf__endianness() will reflect overridden endianness.

Given there are no known use cases for supporting cross-endianness for
.BTF.ext, loading .BTF.ext in non-native endianness is not supported.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200929043046.1324350-3-andriin@fb.com

Move existing ASSERT_xxx() macros out of btf_write selftest into test_progs.h
to use across all selftests. Also expand a set of macros for typical cases.

Now there are the following macros:
  - ASSERT_EQ() -- check for equality of two integers;
  - ASSERT_STREQ() -- check for equality of two C strings;
  - ASSERT_OK() -- check for successful (zero) return result;
  - ASSERT_ERR() -- check for unsuccessful (non-zero) return result;
  - ASSERT_NULL() -- check for NULL pointer;
  - ASSERT_OK_PTR() -- check for a valid pointer;
  - ASSERT_ERR_PTR() -- check for NULL or negative error encoded in a pointer.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200929043046.1324350-2-andriin@fb.com

If programs in prog_tests using skeletons declare the 'skel' variable as
global but not static, that will lead to linker errors on the final link of
the prog_tests binary due to duplicate symbols. Fix a few instances of this.

Fixes: b18c1f0a ("bpf: selftest: Adapt sock_fields test to use skel and global variables")
Fixes: 9a856cae ("bpf: selftest: Add test_btf_skc_cls_ingress")
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200929123026.46751-1-toke@redhat.com

After 'peeking' the ring, the consumer, not the producer, reads the data.
Fix this mistake in the comments.

Fixes: 15d8c916 ("xsk: Add function naming comments and reorder functions")
Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/bpf/20200928082344.17110-1-ciara.loftus@intel.com

The new test for task iteration in bpf_iter checks (in do_btf_read()) if it
should be skipped due to missing __builtin_btf_type_id. However, this
'skip' verdict is not propagated to the caller, so the parent test will
still fail. Fix this by also skipping the rest of the parent test if the
skip condition was reached.

Fixes: b72091bd ("selftests/bpf: Add test for bpf_seq_printf_btf helper")
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Link: https://lore.kernel.org/bpf/20200929123004.46694-1-toke@redhat.com

The Makefile in bpf/preload builds a local copy of libbpf, but does not
properly clean up after itself. This can lead to subsequent compilation
failures, since the feature detection cache is kept around which can lead
subsequent detection to fail.

Fix this by properly setting clean-files, and while we're at it, also add a
.gitignore for the directory to ignore the build artifacts.

Fixes: d71fa5c9 ("bpf: Add kernel module with user mode driver that populates bpffs.")
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200927193005.8459-1-toke@redhat.com

Alan Maguire says:

====================
Resolve issues in bpf selftests introduced with BTF-based kernel data
display selftests; these are

- a warning introduced in snprintf_btf.c; and
- compilation failures with old kernels vmlinux.h
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Andrii reports that bpf selftests relying on "struct btf_ptr" and BTF_F_*
values will not build as vmlinux.h for older kernels will not include
"struct btf_ptr" or the BTF_F_* enum values.  Undefine and redefine
them to work around this.

Fixes: b72091bd ("selftests/bpf: Add test for bpf_seq_printf_btf helper")
Fixes: 076a95f5 ("selftests/bpf: Add bpf_snprintf_btf helper tests")
Reported-by: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/1601379151-21449-3-git-send-email-alan.maguire@oracle.com

Daniel reports:

+    system("ping -c 1 127.0.0.1 > /dev/null");

This generates the following new warning when compiling BPF selftests:

  [...]
  EXT-OBJ  [test_progs] cgroup_helpers.o
  EXT-OBJ  [test_progs] trace_helpers.o
  EXT-OBJ  [test_progs] network_helpers.o
  EXT-OBJ  [test_progs] testing_helpers.o
  TEST-OBJ [test_progs] snprintf_btf.test.o
/root/bpf-next/tools/testing/selftests/bpf/prog_tests/snprintf_btf.c: In function ‘test_snprintf_btf’:
/root/bpf-next/tools/testing/selftests/bpf/prog_tests/snprintf_btf.c:30:2: warning: ignoring return value of ‘system’, declared with attribute warn_unused_result [-Wunused-result]
  system("ping -c 1 127.0.0.1 > /dev/null");
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  [...]

Fixes: 076a95f5 ("selftests/bpf: Add bpf_snprintf_btf helper tests")
Reported-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/1601379151-21449-2-git-send-email-alan.maguire@oracle.com

Fix warning in bpf selftests,

progs/test_raw_tp_test_run.c:18:10: warning: cast to smaller integer type 'int' from 'struct task_struct *' [-Wpointer-to-int-cast]

Change int type cast to long to fix. Discovered with gcc-9 and llvm-11+
where llvm was recent main branch.

Fixes: 09d8ad16 ("selftests/bpf: Add raw_tp_test_run")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/160134424745.11199.13841922833336698133.stgit@john-Precision-5820-Tower

Andrii Nakryiko says:

====================
This patch set introduces a new set of BTF APIs to libbpf that allow to
conveniently produce BTF types and strings. These APIs will allow libbpf to do
more intrusive modifications of program's BTF (by rewriting it, at least as of
right now), which is necessary for the upcoming libbpf static linking. But
they are complete and generic, so can be adopted by anyone who has a need to
produce BTF type information.

One such example outside of libbpf is pahole, which was actually converted to
these APIs (locally, pending landing of these changes in libbpf) completely
and shows reduction in amount of custom pahole code necessary and brings nice
savings in memory usage (about 370MB reduction at peak for my kernel
configuration) and even BTF deduplication times (one second reduction,
23.7s -> 22.7s). Memory savings are due to avoiding pahole's own copy of
"uncompressed" raw BTF data. Time reduction comes from faster string
search and deduplication by relying on hashmap instead of BST used by pahole's
own code. Consequently, these APIs are already tested on real-world
complicated kernel BTF, but there is also pretty extensive selftest doing
extra validations.

Selftests in patch #3 add a set of generic ASSERT_{EQ,STREQ,ERR,OK} macros
that are useful for writing shorter and less repretitive selftests. I decided
to keep them local to that selftest for now, but if they prove to be useful in
more contexts we should move them to test_progs.h. And few more (e.g.,
inequality tests) macros are probably necessary to have a more complete set.

Cc: Arnaldo Carvalho de Melo <acme@redhat.com>

v2->v3:
  - resending original patches #7-9 as patches #1-3 due to merge conflict;

v1->v2:
  - fixed comments (John);
  - renamed btf__append_xxx() into btf__add_xxx() (Alexei);
  - added btf__find_str() in addition to btf__add_str();
  - btf__new_empty() now sets kernel FD to -1 initially.
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Add selftests for BTF writer APIs.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200929020533.711288-4-andriin@fb.com

BTF strings are used not just for names, they can be arbitrary strings used
for CO-RE relocations, line/func infos, etc. Thus "name_by_offset" terminology
is too specific and might be misleading. Instead, introduce
btf__str_by_offset() API which uses generic string terminology.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200929020533.711288-3-andriin@fb.com

Add APIs for appending new BTF types at the end of BTF object.

Each BTF kind has either one API of the form btf__add_<kind>(). For types
that have variable amount of additional items (struct/union, enum, func_proto,
datasec), additional API is provided to emit each such item. E.g., for
emitting a struct, one would use the following sequence of API calls:

btf__add_struct(...);
btf__add_field(...);
...
btf__add_field(...);

Each btf__add_field() will ensure that the last BTF type is of STRUCT or
UNION kind and will automatically increment that type's vlen field.

All the strings are provided as C strings (const char *), not a string offset.
This significantly improves usability of BTF writer APIs. All such strings
will be automatically appended to string section or existing string will be
re-used, if such string was already added previously.

Each API attempts to do all the reasonable validations, like enforcing
non-empty names for entities with required names, proper value bounds, various
bit offset restrictions, etc.

Type ID validation is minimal because it's possible to emit a type that refers
to type that will be emitted later, so libbpf has no way to enforce such
cases. User must be careful to properly emit all the necessary types and
specify type IDs that will be valid in the finally generated BTF.

Each of btf__add_<kind>() APIs return new type ID on success or negative
value on error. APIs like btf__add_field() that emit additional items
return zero on success and negative value on error.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200929020533.711288-2-andriin@fb.com

Alan Maguire says:

====================
This series attempts to provide a simple way for BPF programs (and in
future other consumers) to utilize BPF Type Format (BTF) information
to display kernel data structures in-kernel.  The use case this
functionality is applied to here is to support a snprintf()-like
helper to copy a BTF representation of kernel data to a string,
and a BPF seq file helper to display BTF data for an iterator.

There is already support in kernel/bpf/btf.c for "show" functionality;
the changes here generalize that support from seq-file specific
verifier display to the more generic case and add another specific
use case; rather than seq_printf()ing the show data, it is copied
to a supplied string using a snprintf()-like function.  Other future
consumers of the show functionality could include a bpf_printk_btf()
function which printk()ed the data instead.  Oops messaging in
particular would be an interesting application for such functionality.

The above potential use case hints at a potential reply to
a reasonable objection that such typed display should be
solved by tracing programs, where the in-kernel tracing records
data and the userspace program prints it out.  While this
is certainly the recommended approach for most cases, I
believe having an in-kernel mechanism would be valuable
also.  Critically in BPF programs it greatly simplifies
debugging and tracing of such data to invoking a simple
helper.

One challenge raised in an earlier iteration of this work -
where the BTF printing was implemented as a printk() format
specifier - was that the amount of data printed per
printk() was large, and other format specifiers were far
simpler.  Here we sidestep that concern by printing
components of the BTF representation as we go for the
seq file case, and in the string case the snprintf()-like
operation is intended to be a basis for perf event or
ringbuf output.  The reasons for avoiding bpf_trace_printk
are that

1. bpf_trace_printk() strings are restricted in size and
cannot display anything beyond trivial data structures; and
2. bpf_trace_printk() is for debugging purposes only.

As Alexei suggested, a bpf_trace_puts() helper could solve
this in the future but it still would be limited by the
1000 byte limit for traced strings.

Default output for an sk_buff looks like this (zeroed fields
are omitted):

(struct sk_buff){
 .transport_header = (__u16)65535,
 .mac_header = (__u16)65535,
 .end = (sk_buff_data_t)192,
 .head = (unsigned char *)0x000000007524fd8b,
 .data = (unsigned char *)0x000000007524fd8b,
 .truesize = (unsigned int)768,
 .users = (refcount_t){
  .refs = (atomic_t){
   .counter = (int)1,
  },
 },
}

Flags can modify aspects of output format; see patch 3
for more details.

Changes since v6:

- Updated safe data size to 32, object name size to 80.
  This increases the number of safe copies done, but performance is
  not a key goal here. WRT name size the largest type name length
  in bpf-next according to "pahole -s" is 64 bytes, so that still gives
  room for additional type qualifiers, parens etc within the name limit
  (Alexei, patch 2)
- Remove inlines and converted as many #defines to functions as was
  possible.  In a few cases - btf_show_type_value[s]() specifically -
  I left these as macros as btf_show_type_value[s]() prepends and
  appends format strings to the format specifier (in order to include
  indentation, delimiters etc so a macro makes that simpler (Alexei,
  patch 2)
- Handle btf_resolve_size() error in btf_show_obj_safe() (Alexei, patch 2)
- Removed clang loop unroll in BTF snprintf test (Alexei)
- switched to using bpf_core_type_id_kernel(type) as suggested by Andrii,
  and Alexei noted that __builtin_btf_type_id(,1) should be used (patch 4)
- Added skip logic if __builtin_btf_type_id is not available (patches 4,8)
- Bumped limits on bpf iters to support printing larger structures (Alexei,
  patch 5)
- Updated overflow bpf_iter tests to reflect new iter max size (patch 6)
- Updated seq helper to use type id only (Alexei, patch 7)
- Updated BTF task iter test to use task struct instead of struct fs_struct
  since new limits allow a task_struct to be displayed (patch 8)
- Fixed E2BIG handling in iter task (Alexei, patch 8)

Changes since v5:

- Moved btf print prepare into patch 3, type show seq
  with flags into patch 2 (Alexei, patches 2,3)
- Fixed build bot warnings around static declarations
  and printf attributes
- Renamed functions to snprintf_btf/seq_printf_btf
  (Alexei, patches 3-6)

Changes since v4:

- Changed approach from a BPF trace event-centric design to one
  utilizing a snprintf()-like helper and an iter helper (Alexei,
  patches 3,5)
- Added tests to verify BTF output (patch 4)
- Added support to tests for verifying BTF type_id-based display
  as well as type name via __builtin_btf_type_id (Andrii, patch 4).
- Augmented task iter tests to cover the BTF-based seq helper.
  Because a task_struct's BTF-based representation would overflow
  the PAGE_SIZE limit on iterator data, the "struct fs_struct"
  (task->fs) is displayed for each task instead (Alexei, patch 6).

Changes since v3:

- Moved to RFC since the approach is different (and bpf-next is
  closed)
- Rather than using a printk() format specifier as the means
  of invoking BTF-enabled display, a dedicated BPF helper is
  used.  This solves the issue of printk() having to output
  large amounts of data using a complex mechanism such as
  BTF traversal, but still provides a way for the display of
  such data to be achieved via BPF programs.  Future work could
  include a bpf_printk_btf() function to invoke display via
  printk() where the elements of a data structure are printk()ed
 one at a time.  Thanks to Petr Mladek, Andy Shevchenko and
  Rasmus Villemoes who took time to look at the earlier printk()
  format-specifier-focused version of this and provided feedback
  clarifying the problems with that approach.
- Added trace id to the bpf_trace_printk events as a means of
  separating output from standard bpf_trace_printk() events,
  ensuring it can be easily parsed by the reader.
- Added bpf_trace_btf() helper tests which do simple verification
  of the various display options.

Changes since v2:

- Alexei and Yonghong suggested it would be good to use
  probe_kernel_read() on to-be-shown data to ensure safety
  during operation.  Safe copy via probe_kernel_read() to a
  buffer object in "struct btf_show" is used to support
  this.  A few different approaches were explored
  including dynamic allocation and per-cpu buffers. The
  downside of dynamic allocation is that it would be done
  during BPF program execution for bpf_trace_printk()s using
  %pT format specifiers. The problem with per-cpu buffers
  is we'd have to manage preemption and since the display
  of an object occurs over an extended period and in printk
  context where we'd rather not change preemption status,
  it seemed tricky to manage buffer safety while considering
  preemption.  The approach of utilizing stack buffer space
  via the "struct btf_show" seemed like the simplest approach.
  The stack size of the associated functions which have a
  "struct btf_show" on their stack to support show operation
  (btf_type_snprintf_show() and btf_type_seq_show()) stays
  under 500 bytes. The compromise here is the safe buffer we
  use is small - 256 bytes - and as a result multiple
  probe_kernel_read()s are needed for larger objects. Most
  objects of interest are smaller than this (e.g.
  "struct sk_buff" is 224 bytes), and while task_struct is a
  notable exception at ~8K, performance is not the priority for
  BTF-based display. (Alexei and Yonghong, patch 2).
- safe buffer use is the default behaviour (and is mandatory
  for BPF) but unsafe display - meaning no safe copy is done
  and we operate on the object itself - is supported via a
  'u' option.
- pointers are prefixed with 0x for clarity (Alexei, patch 2)
- added additional comments and explanations around BTF show
  code, especially around determining whether objects such
  zeroed. Also tried to comment safe object scheme used. (Yonghong,
  patch 2)
- added late_initcall() to initialize vmlinux BTF so that it would
  not have to be initialized during printk operation (Alexei,
  patch 5)
- removed CONFIG_BTF_PRINTF config option as it is not needed;
  CONFIG_DEBUG_INFO_BTF can be used to gate test behaviour and
  determining behaviour of type-based printk can be done via
  retrieval of BTF data; if it's not there BTF was unavailable
  or broken (Alexei, patches 4,6)
- fix bpf_trace_printk test to use vmlinux.h and globals via
  skeleton infrastructure, removing need for perf events
  (Andrii, patch 8)

Changes since v1:

- changed format to be more drgn-like, rendering indented type info
  along with type names by default (Alexei)
- zeroed values are omitted (Arnaldo) by default unless the '0'
  modifier is specified (Alexei)
- added an option to print pointer values without obfuscation.
  The reason to do this is the sysctls controlling pointer display
  are likely to be irrelevant in many if not most tracing contexts.
  Some questions on this in the outstanding questions section below...
- reworked printk format specifer so that we no longer rely on format
  %pT<type> but instead use a struct * which contains type information
  (Rasmus). This simplifies the printk parsing, makes use more dynamic
  and also allows specification by BTF id as well as name.
- removed incorrect patch which tried to fix dereferencing of resolved
  BTF info for vmlinux; instead we skip modifiers for the relevant
  case (array element type determination) (Alexei).
- fixed issues with negative snprintf format length (Rasmus)
- added test cases for various data structure formats; base types,
  typedefs, structs, etc.
- tests now iterate through all typedef, enum, struct and unions
  defined for vmlinux BTF and render a version of the target dummy
  value which is either all zeros or all 0xff values; the idea is this
  exercises the "skip if zero" and "print everything" cases.
- added support in BPF for using the %pT format specifier in
  bpf_trace_printk()
- added BPF tests which ensure %pT format specifier use works (Alexei).
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Add a test verifying iterating over tasks and displaying BTF
representation of task_struct succeeds.
Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/1601292670-1616-9-git-send-email-alan.maguire@oracle.com

A helper is added to allow seq file writing of kernel data
structures using vmlinux BTF.  Its signature is

long bpf_seq_printf_btf(struct seq_file *m, struct btf_ptr *ptr,
                        u32 btf_ptr_size, u64 flags);

Flags and struct btf_ptr definitions/use are identical to the
bpf_snprintf_btf helper, and the helper returns 0 on success
or a negative error value.
Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/1601292670-1616-8-git-send-email-alan.maguire@oracle.com

bpf iter size increase to PAGE_SIZE << 3 means overflow tests assuming
page size need to be bumped also.
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/1601292670-1616-7-git-send-email-alan.maguire@oracle.com

BPF iter size is limited to PAGE_SIZE; if we wish to display BTF-based
representations of larger kernel data structures such as task_struct,
this will be insufficient.
Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/1601292670-1616-6-git-send-email-alan.maguire@oracle.com

Tests verifying snprintf()ing of various data structures,
flags combinations using a tp_btf program. Tests are skipped
if __builtin_btf_type_id is not available to retrieve BTF
type ids.
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/1601292670-1616-5-git-send-email-alan.maguire@oracle.com

A helper is added to support tracing kernel type information in BPF
using the BPF Type Format (BTF).  Its signature is

long bpf_snprintf_btf(char *str, u32 str_size, struct btf_ptr *ptr,
		      u32 btf_ptr_size, u64 flags);

struct btf_ptr * specifies

- a pointer to the data to be traced
- the BTF id of the type of data pointed to
- a flags field is provided for future use; these flags
  are not to be confused with the BTF_F_* flags
  below that control how the btf_ptr is displayed; the
  flags member of the struct btf_ptr may be used to
  disambiguate types in kernel versus module BTF, etc;
  the main distinction is the flags relate to the type
  and information needed in identifying it; not how it
  is displayed.

For example a BPF program with a struct sk_buff *skb
could do the following:

	static struct btf_ptr b = { };

	b.ptr = skb;
	b.type_id = __builtin_btf_type_id(struct sk_buff, 1);
	bpf_snprintf_btf(str, sizeof(str), &b, sizeof(b), 0, 0);

Default output looks like this:

(struct sk_buff){
 .transport_header = (__u16)65535,
 .mac_header = (__u16)65535,
 .end = (sk_buff_data_t)192,
 .head = (unsigned char *)0x000000007524fd8b,
 .data = (unsigned char *)0x000000007524fd8b,
 .truesize = (unsigned int)768,
 .users = (refcount_t){
  .refs = (atomic_t){
   .counter = (int)1,
  },
 },
}

Flags modifying display are as follows:

- BTF_F_COMPACT:	no formatting around type information
- BTF_F_NONAME:		no struct/union member names/types
- BTF_F_PTR_RAW:	show raw (unobfuscated) pointer values;
			equivalent to %px.
- BTF_F_ZERO:		show zero-valued struct/union members;
			they are not displayed by default
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/1601292670-1616-4-git-send-email-alan.maguire@oracle.com

generalize the "seq_show" seq file support in btf.c to support
a generic show callback of which we support two instances; the
current seq file show, and a show with snprintf() behaviour which
instead writes the type data to a supplied string.

Both classes of show function call btf_type_show() with different
targets; the seq file or the string to be written.  In the string
case we need to track additional data - length left in string to write
and length to return that we would have written (a la snprintf).

By default show will display type information, field members and
their types and values etc, and the information is indented
based upon structure depth. Zeroed fields are omitted.

Show however supports flags which modify its behaviour:

BTF_SHOW_COMPACT - suppress newline/indent.
BTF_SHOW_NONAME - suppress show of type and member names.
BTF_SHOW_PTR_RAW - do not obfuscate pointer values.
BTF_SHOW_UNSAFE - do not copy data to safe buffer before display.
BTF_SHOW_ZERO - show zeroed values (by default they are not shown).
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/1601292670-1616-3-git-send-email-alan.maguire@oracle.com

It will be used later for BPF structure display support
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/1601292670-1616-2-git-send-email-alan.maguire@oracle.com

Add an ability to create an empty BTF object from scratch. This is going to be
used by pahole for BTF encoding. And also by selftest for convenient creation
of BTF objects.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200926011357.2366158-7-andriin@fb.com

Allow internal BTF representation to switch from default read-only mode, in
which raw BTF data is a single non-modifiable block of memory with BTF header,
types, and strings layed out sequentially and contiguously in memory, into
a writable representation with types and strings data split out into separate
memory regions, that can be dynamically expanded.

Such writable internal representation is transparent to users of libbpf APIs,
but allows to append new types and strings at the end of BTF, which is
a typical use case when generating BTF programmatically. All the basic
guarantees of BTF types and strings layout is preserved, i.e., user can get
`struct btf_type *` pointer and read it directly. Such btf_type pointers might
be invalidated if BTF is modified, so some care is required in such mixed
read/write scenarios.

Switch from read-only to writable configuration happens automatically the
first time when user attempts to modify BTF by either adding a new type or new
string. It is still possible to get raw BTF data, which is a single piece of
memory that can be persisted in ELF section or into a file as raw BTF. Such
raw data memory is also still owned by BTF and will be freed either when BTF
object is freed or if another modification to BTF happens, as any modification
invalidates BTF raw representation.

This patch adds the first two BTF manipulation APIs: btf__add_str(), which
allows to add arbitrary strings to BTF string section, and btf__find_str()
which allows to find existing string offset, but not add it if it's missing.
All the added strings are automatically deduplicated. This is achieved by
maintaining an additional string lookup index for all unique strings. Such
index is built when BTF is switched to modifiable mode. If at that time BTF
strings section contained duplicate strings, they are not de-duplicated. This
is done specifically to not modify the existing content of BTF (types, their
string offsets, etc), which can cause confusion and is especially important
property if there is struct btf_ext associated with struct btf. By following
this "imperfect deduplication" process, btf_ext is kept consitent and correct.
If deduplication of strings is necessary, it can be forced by doing BTF
deduplication, at which point all the strings will be eagerly deduplicated and
all string offsets both in struct btf and struct btf_ext will be updated.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200926011357.2366158-6-andriin@fb.com

Calculating a hash of zero-terminated string is a common need when using
hashmap, so extract it for reuse.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200926011357.2366158-5-andriin@fb.com

Managing dynamically-sized array is a common, but not trivial functionality,
which significant amount of logic and code to implement properly. So instead
of re-implementing it all the time, extract it into a helper function ans
reuse.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200926011357.2366158-4-andriin@fb.com

Refactor internals of struct btf to remove assumptions that BTF header, type
data, and string data are layed out contiguously in a memory in a single
memory allocation. Now we have three separate pointers pointing to the start
of each respective are: header, types, strings. In the next patches, these
pointers will be re-assigned to point to independently allocated memory areas,
if BTF needs to be modified.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200926011357.2366158-3-andriin@fb.com

Refactor implementation of internal BTF type index to not use direct pointers.
Instead it uses offset relative to the start of types data section. This
allows for types data to be reallocatable, enabling implementation of
modifiable BTF.

As now getting type by ID has an extra indirection step, convert all internal
type lookups to a new helper btf_type_id(), that returns non-const pointer to
a type by its ID.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200926011357.2366158-2-andriin@fb.com

The test_overhead prog_test included an fmod_ret program that attached to
__set_task_comm() in the kernel. However, this function was never listed as
allowed for return modification, so this only worked because of the
verifier skipping tests when a trampoline already existed for the attach
point. Now that the verifier checks have been fixed, remove fmod_ret from
the test so it works again.

Fixes: 4eaf0b5c ("selftest/bpf: Fmod_ret prog and implement test_overhead as part of bench")
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

The check_attach_btf_id() function really does three things:

1. It performs a bunch of checks on the program to ensure that the
   attachment is valid.

2. It stores a bunch of state about the attachment being requested in
   the verifier environment and struct bpf_prog objects.

3. It allocates a trampoline for the attachment.

This patch splits out (1.) and (3.) into separate functions which will
perform the checks, but return the computed values instead of directly
modifying the environment. This is done in preparation for reusing the
checks when the actual attachment is happening, which will allow tracing
programs to have multiple (compatible) attachments.

This also fixes a bug where a bunch of checks were skipped if a trampoline
already existed for the tracing target.

Fixes: 6ba43b76 ("bpf: Attachment verification for BPF_MODIFY_RETURN")
Fixes: 1e6c62a8 ("bpf: Introduce sleepable BPF programs")
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

In preparation for moving code around, change a bunch of references to
env->log (and the verbose() logging helper) to use bpf_log() and a direct
pointer to struct bpf_verifier_log. While we're touching the function
signature, mark the 'prog' argument to bpf_check_type_match() as const.

Also enhance the bpf_verifier_log_needed() check to handle NULL pointers
for the log struct so we can re-use the code with logging disabled.
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

From the checks and commit messages for modify_return, it seems it was
never the intention that it should be possible to attach a tracing program
with expected_attach_type == BPF_MODIFY_RETURN to another BPF program.
However, check_attach_modify_return() will only look at the function name,
so if the target function starts with "security_", the attach will be
allowed even for bpf2bpf attachment.

Fix this oversight by also blocking the modification if a target program is
supplied.

Fixes: 18644cec ("bpf: Fix use-after-free in fmod_ret check")
Fixes: 6ba43b76 ("bpf: Attachment verification for BPF_MODIFY_RETURN")
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Lorenz Bauer says:

====================
Changes in v2:
- Check sk_fullsock in map_update_elem (Martin)

Enable calling map_update_elem on sockmaps from bpf_iter context. This
in turn allows us to copy a sockmap by iterating its elements.

The change itself is tiny, all thanks to the ground work from Martin,
whose series [1] this patch is based on. I updated the tests to do some
copying, and also included two cleanups.

I'm sending this out now rather than when Martin's series has landed
because I hope this can get in before the merge window (potentially)
closes this weekend.

1: https://lore.kernel.org/bpf/20200925000337.3853598-1-kafai@fb.com/
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Since we can now call map_update_elem(sockmap) from bpf_iter context
it's possible to copy a sockmap or sockhash in the kernel. Add a
selftest which exercises this.
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200928090805.23343-5-lmb@cloudflare.com

The shared header to define SOCKMAP_MAX_ENTRIES is a bit overkill.
Dynamically allocate the sock_fd array based on bpf_map__max_entries
instead.
Suggested-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200928090805.23343-4-lmb@cloudflare.com

We compare socket cookies to ensure that insertion into a sockmap worked.
Pull this out into a helper function for use in other tests.
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200928090805.23343-3-lmb@cloudflare.com

Allow passing a pointer to a BTF struct sock_common* when updating
a sockmap or sockhash. Since BTF pointers can fault and therefore be
NULL at runtime we need to add an additional !sk check to
sock_map_update_elem. Since we may be passed a request or timewait
socket we also need to check sk_fullsock. Doing this allows calling
map_update_elem on sockmap from bpf_iter context, which uses
BTF pointers.
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200928090805.23343-2-lmb@cloudflare.com