Commit [0] breaks samples/bpf build:

    $ make M=samples/bpf
    ...
    make -C /path/to/kernel/samples/bpf/../../tools/lib/bpf \
     ...
     EXTRA_CFLAGS=" \
     ...
     -fsanitize=bounds \
     -I/path/to/kernel/usr/include \
     ...
    	/path/to/kernel/samples/bpf/libbpf/libbpf.a install_headers
      CC      /path/to/kernel/samples/bpf/libbpf/staticobjs/libbpf.o
    In file included from libbpf.c:29:
    /path/to/kernel/tools/include/linux/err.h:35:8: error: 'inline' can only appear on functions
       35 | static inline void * __must_check ERR_PTR(long error_)
          |        ^

The error is caused by `objtree` variable changing definition from `.`
(dot) to an absolute path:
- The variable TPROGS_CFLAGS is constructed as follows:
  ...
  TPROGS_CFLAGS += -I$(objtree)/usr/include
- It is passed as EXTRA_CFLAGS for libbpf compilation:
  $(LIBBPF): ...
    ...
	$(MAKE) -C $(LIBBPF_SRC) RM='rm -rf' EXTRA_CFLAGS="$(TPROGS_CFLAGS)"
- Before commit [0], the line passed to libbpf makefile was
  '-I./usr/include', where '.' referred to LIBBPF_SRC due to -C flag.
  The directory $(LIBBPF_SRC)/usr/include does not exist and thus
  was never resolved by C compiler.
- After commit [0], the line passed to libbpf makefile became:
  '<output-dir>/usr/include', this directory exists and is resolved by
  C compiler.
- Both 'tools/include' and 'usr/include' define files err.h and types.h.
- libbpf expects headers like 'linux/err.h' and 'linux/types.h'
  defined in 'tools/include', not 'usr/include', hence the compilation
  error.

This commit removes unnecessary -I flags from libbpf compilation.
(libbpf sets up the necessary includes at lib/bpf/Makefile:63).

Changes v1 [1] -> v2:
- dropped unnecessary replacement of KBUILD_OUTPUT with $(objtree)
  (Andrii)
Changes v2 [2] -> v3:
- make sure --sysroot option is set for libbpf's EXTRA_CFLAGS,
  if $(SYSROOT) is set (Stanislav)

[0] commit 13b25489b6f8 ("kbuild: change working directory to external module directory with M=")
[1] https://lore.kernel.org/bpf/20241202212154.3174402-1-eddyz87@gmail.com/
[2] https://lore.kernel.org/bpf/20241202234741.3492084-1-eddyz87@gmail.com/

Fixes: 13b25489b6f8 ("kbuild: change working directory to external module directory with M=")
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://lore.kernel.org/bpf/20241203182222.3915763-1-eddyz87@gmail.com

The samples/bpf has become outdated and often does not follow up with
the latest. This commit removes obsolete tracing-related tests.

Specifically, 'test_overhead' is duplicate with selftests (and bench),
and 'test_override_return', 'test_probe_write_user' tests are obsolete
since they have been replaced by kprobe_multi_override and probe_user
from selftests respectively.

The following files are removed:
- test_overhead: tests the overhead of BPF programs with task_rename,
  now covered by selftests and benchmark tests (rename-*). [1]

- test_override_return: tests the return override functionality, now
  handled by kprobe_multi_override in selftests.

- test_probe_write_user: tests the probe_write_user functionality,
  now replaced by the probe_user test in selftests.

This cleanup will help to streamline the testing framework by removing
redundant tests.

[1]: https://patchwork.kernel.org/cover/13759916

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Link: https://lore.kernel.org/r/20241011044847.51584-5-danieltimlee@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

This patch removes the obsolete cgroup related tests. These tests are
now redundant because their functionality is already covered by more
modern and comprehensive tests under selftests/bpf.

The following files are removed:
- test_current_task_under_cgroup: tests bpf_current_task_under_cgroup()
  to check if a task belongs to a cgroup. Already covered by
  task_under_cgroup at selftest and other cgroup ID tests.

- test_cgrp2_tc: tests bpf_skb_under_cgroup() to filter packets based
  on cgroup. This behavior is now validated by cgroup_skb_sk_lookup,
  which uses bpf_skb_cgroup_id, making this test redundant.

By removing these outdated tests, this patch helps streamline and
modernize the test suite, avoiding duplication of test coverage.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Link: https://lore.kernel.org/r/20241011044847.51584-4-danieltimlee@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

This patch continues the migration and removal process for cgroup
sock_create tests to selftests.

The test being migrated verifies the ability of cgroup BPF to block the
creation of specific types of sockets using a verdict. Specifically, the
test denies socket creation when the socket is of type AF_INET{6},
SOCK_DGRAM, and IPPROTO_ICMP{V6}. If the requested socket type matches
these attributes, the cgroup BPF verdict blocks the socket creation.

As with the previous commit, this test currently lacks coverage in
selftests, so this patch migrates the functionality into the sock_create
tests under selftests. This migration ensures that the socket creation
blocking behavior with cgroup bpf program is properly tested within the
selftest framework.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Link: https://lore.kernel.org/r/20241011044847.51584-3-danieltimlee@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

This patch migrates the old test for cgroup BPF that sets
sk_bound_dev_if, mark, and priority when AF_INET{6} sockets are created.
The most closely related tests under selftests are 'test_sock' and
'sockopt'. However, these existing tests serve different purposes.
'test_sock' focuses mainly on verifying the socket binding process,
while 'sockopt' concentrates on testing the behavior of getsockopt and
setsockopt operations for various socket options.

Neither of these existing tests directly covers the ability of cgroup
BPF to set socket attributes such as sk_bound_dev_if, mark, and priority
during socket creation. To address this gap, this patch introduces a
migration of the old cgroup socket attribute test, now included as the
'sock_create' test in selftests/bpf. This ensures that the ability to
configure these attributes during socket creation is properly tested.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Link: https://lore.kernel.org/r/20241011044847.51584-2-danieltimlee@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

In commit ba8de796baf4 ("net: introduce sk_skb_reason_drop function")
kfree_skb_reason() becomes an inline function and cannot be traced.

samples/bpf is abandonware by now, and we should slowly but surely
convert whatever makes sense into BPF selftests under
tools/testing/selftests/bpf and just get rid of the rest.

Link: https://github.com/torvalds/linux/commit/ba8de796baf4bdc03530774fb284fe3c97875566
Signed-off-by: Rong Tao <rongtao@cestc.cn>
Link: https://lore.kernel.org/r/tencent_30ADAC88CB2915CA57E9512D4460035BA107@qq.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Currently, compiling the bpf programs will result the compilation errors
with the cf-protection option as follows in arm64 and loongarch64 machine
when using gcc 12.3.1 and clang 17.0.6. This commit fixes the compilation
errors by limited the cf-protection option only used in x86 platform.

[root@localhost linux]# make M=samples/bpf
	......
  CLANG-bpf  samples/bpf/xdp2skb_meta_kern.o
error: option 'cf-protection=return' cannot be specified on this target
error: option 'cf-protection=branch' cannot be specified on this target
2 errors generated.
  CLANG-bpf  samples/bpf/syscall_tp_kern.o
error: option 'cf-protection=return' cannot be specified on this target
error: option 'cf-protection=branch' cannot be specified on this target
2 errors generated.
	......

Fixes: 34f6e38f58db ("samples/bpf: fix warning with ignored-attributes")
Reported-by: Jiangshan Yi <yijiangshan@kylinos.cn>
Signed-off-by: Jiangshan Yi <yijiangshan@kylinos.cn>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Qiang Wang <wangqiang1@kylinos.cn>
Link: https://lore.kernel.org/bpf/20240815135524.140675-1-13667453960@163.com

Pull Kbuild updates from Masahiro Yamada:

 - Avoid 'constexpr', which is a keyword in C23

 - Allow 'dtbs_check' and 'dt_compatible_check' run independently of
   'dt_binding_check'

 - Fix weak references to avoid GOT entries in position-independent code
   generation

 - Convert the last use of 'optional' property in arch/sh/Kconfig

 - Remove support for the 'optional' property in Kconfig

 - Remove support for Clang's ThinLTO caching, which does not work with
   the .incbin directive

 - Change the semantics of $(src) so it always points to the source
   directory, which fixes Makefile inconsistencies between upstream and
   downstream

 - Fix 'make tar-pkg' for RISC-V to produce a consistent package

 - Provide reasonable default coverage for objtool, sanitizers, and
   profilers

 - Remove redundant OBJECT_FILES_NON_STANDARD, KASAN_SANITIZE, etc.

 - Remove the last use of tristate choice in drivers/rapidio/Kconfig

 - Various cleanups and fixes in Kconfig

* tag 'kbuild-v6.10' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (46 commits)
  kconfig: use sym_get_choice_menu() in sym_check_prop()
  rapidio: remove choice for enumeration
  kconfig: lxdialog: remove initialization with A_NORMAL
  kconfig: m/nconf: merge two item_add_str() calls
  kconfig: m/nconf: remove dead code to display value of bool choice
  kconfig: m/nconf: remove dead code to display children of choice members
  kconfig: gconf: show checkbox for choice correctly
  kbuild: use GCOV_PROFILE and KCSAN_SANITIZE in scripts/Makefile.modfinal
  Makefile: remove redundant tool coverage variables
  kbuild: provide reasonable defaults for tool coverage
  modules: Drop the .export_symbol section from the final modules
  kconfig: use menu_list_for_each_sym() in sym_check_choice_deps()
  kconfig: use sym_get_choice_menu() in conf_write_defconfig()
  kconfig: add sym_get_choice_menu() helper
  kconfig: turn defaults and additional prompt for choice members into error
  kconfig: turn missing prompt for choice members into error
  kconfig: turn conf_choice() into void function
  kconfig: use linked list in sym_set_changed()
  kconfig: gconf: use MENU_CHANGED instead of SYMBOL_CHANGED
  kconfig: gconf: remove debug code
  ...

Kbuild conventionally uses $(obj)/ for generated files, and $(src)/ for
checked-in source files. It is merely a convention without any functional
difference. In fact, $(obj) and $(src) are exactly the same, as defined
in scripts/Makefile.build:

    src := $(obj)

When the kernel is built in a separate output directory, $(src) does
not accurately reflect the source directory location. While Kbuild
resolves this discrepancy by specifying VPATH=$(srctree) to search for
source files, it does not cover all cases. For example, when adding a
header search path for local headers, -I$(srctree)/$(src) is typically
passed to the compiler.

This introduces inconsistency between upstream and downstream Makefiles
because $(src) is used instead of $(srctree)/$(src) for the latter.

To address this inconsistency, this commit changes the semantics of
$(src) so that it always points to the directory in the source tree.

Going forward, the variables used in Makefiles will have the following
meanings:

  $(obj)     - directory in the object tree
  $(src)     - directory in the source tree  (changed by this commit)
  $(objtree) - the top of the kernel object tree
  $(srctree) - the top of the kernel source tree

Consequently, $(srctree)/$(src) in upstream Makefiles need to be replaced
with $(src).

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

When I use the command 'make M=samples/bpf' to compile samples/bpf code
in ubuntu 22.04, the error info occured:
Cannot find a vmlinux for VMLINUX_BTF at any of "  /home/ubuntu/code/linux/vmlinux",
build the kernel or set VMLINUX_BTF or VMLINUX_H variable

Others often encounter this kind of issue, new kernel has the vmlinux, so we can
set the path in error info which seems more intuitive, like:
Cannot find a vmlinux for VMLINUX_BTF at any of "  /home/ubuntu/code/linux/vmlinux",
buiild the kernel or set VMLINUX_BTF like "VMLINUX_BTF=/sys/kernel/btf/vmlinux" or
VMLINUX_H variable

Signed-off-by: Tao Chen <chen.dylane@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240428161032.239043-1-chen.dylane@gmail.com