1================================= 2HOWTO interact with BPF subsystem 3================================= 4 5This document provides information for the BPF subsystem about various 6workflows related to reporting bugs, submitting patches, and queueing 7patches for stable kernels. 8 9For general information about submitting patches, please refer to 10`Documentation/process/`_. This document only describes additional specifics 11related to BPF. 12 13.. contents:: 14 :local: 15 :depth: 2 16 17Reporting bugs 18============== 19 20Q: How do I report bugs for BPF kernel code? 21-------------------------------------------- 22A: Since all BPF kernel development as well as bpftool and iproute2 BPF 23loader development happens through the bpf kernel mailing list, 24please report any found issues around BPF to the following mailing 25list: 26 27 bpf@vger.kernel.org 28 29This may also include issues related to XDP, BPF tracing, etc. 30 31Given netdev has a high volume of traffic, please also add the BPF 32maintainers to Cc (from kernel ``MAINTAINERS`` file): 33 34* Alexei Starovoitov <ast@kernel.org> 35* Daniel Borkmann <daniel@iogearbox.net> 36 37In case a buggy commit has already been identified, make sure to keep 38the actual commit authors in Cc as well for the report. They can 39typically be identified through the kernel's git tree. 40 41**Please do NOT report BPF issues to bugzilla.kernel.org since it 42is a guarantee that the reported issue will be overlooked.** 43 44Submitting patches 45================== 46 47Q: To which mailing list do I need to submit my BPF patches? 48------------------------------------------------------------ 49A: Please submit your BPF patches to the bpf kernel mailing list: 50 51 bpf@vger.kernel.org 52 53In case your patch has changes in various different subsystems (e.g. 54networking, tracing, security, etc), make sure to Cc the related kernel mailing 55lists and maintainers from there as well, so they are able to review 56the changes and provide their Acked-by's to the patches. 57 58Q: Where can I find patches currently under discussion for BPF subsystem? 59------------------------------------------------------------------------- 60A: All patches that are Cc'ed to netdev are queued for review under netdev 61patchwork project: 62 63 https://patchwork.kernel.org/project/netdevbpf/list/ 64 65Those patches which target BPF, are assigned to a 'bpf' delegate for 66further processing from BPF maintainers. The current queue with 67patches under review can be found at: 68 69 https://patchwork.kernel.org/project/netdevbpf/list/?delegate=121173 70 71Once the patches have been reviewed by the BPF community as a whole 72and approved by the BPF maintainers, their status in patchwork will be 73changed to 'Accepted' and the submitter will be notified by mail. This 74means that the patches look good from a BPF perspective and have been 75applied to one of the two BPF kernel trees. 76 77In case feedback from the community requires a respin of the patches, 78their status in patchwork will be set to 'Changes Requested', and purged 79from the current review queue. Likewise for cases where patches would 80get rejected or are not applicable to the BPF trees (but assigned to 81the 'bpf' delegate). 82 83Q: How do the changes make their way into Linux? 84------------------------------------------------ 85A: There are two BPF kernel trees (git repositories). Once patches have 86been accepted by the BPF maintainers, they will be applied to one 87of the two BPF trees: 88 89 * https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/ 90 * https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/ 91 92The bpf tree itself is for fixes only, whereas bpf-next for features, 93cleanups or other kind of improvements ("next-like" content). This is 94analogous to net and net-next trees for networking. Both bpf and 95bpf-next will only have a master branch in order to simplify against 96which branch patches should get rebased to. 97 98Accumulated BPF patches in the bpf tree will regularly get pulled 99into the net kernel tree. Likewise, accumulated BPF patches accepted 100into the bpf-next tree will make their way into net-next tree. net and 101net-next are both run by David S. Miller. From there, they will go 102into the kernel mainline tree run by Linus Torvalds. To read up on the 103process of net and net-next being merged into the mainline tree, see 104the :ref:`netdev-FAQ` 105 106 107 108Occasionally, to prevent merge conflicts, we might send pull requests 109to other trees (e.g. tracing) with a small subset of the patches, but 110net and net-next are always the main trees targeted for integration. 111 112The pull requests will contain a high-level summary of the accumulated 113patches and can be searched on netdev kernel mailing list through the 114following subject lines (``yyyy-mm-dd`` is the date of the pull 115request):: 116 117 pull-request: bpf yyyy-mm-dd 118 pull-request: bpf-next yyyy-mm-dd 119 120Q: How do I indicate which tree (bpf vs. bpf-next) my patch should be applied to? 121--------------------------------------------------------------------------------- 122 123A: The process is the very same as described in the :ref:`netdev-FAQ`, 124so please read up on it. The subject line must indicate whether the 125patch is a fix or rather "next-like" content in order to let the 126maintainers know whether it is targeted at bpf or bpf-next. 127 128For fixes eventually landing in bpf -> net tree, the subject must 129look like:: 130 131 git format-patch --subject-prefix='PATCH bpf' start..finish 132 133For features/improvements/etc that should eventually land in 134bpf-next -> net-next, the subject must look like:: 135 136 git format-patch --subject-prefix='PATCH bpf-next' start..finish 137 138If unsure whether the patch or patch series should go into bpf 139or net directly, or bpf-next or net-next directly, it is not a 140problem either if the subject line says net or net-next as target. 141It is eventually up to the maintainers to do the delegation of 142the patches. 143 144If it is clear that patches should go into bpf or bpf-next tree, 145please make sure to rebase the patches against those trees in 146order to reduce potential conflicts. 147 148In case the patch or patch series has to be reworked and sent out 149again in a second or later revision, it is also required to add a 150version number (``v2``, ``v3``, ...) into the subject prefix:: 151 152 git format-patch --subject-prefix='PATCH bpf-next v2' start..finish 153 154When changes have been requested to the patch series, always send the 155whole patch series again with the feedback incorporated (never send 156individual diffs on top of the old series). 157 158Q: What does it mean when a patch gets applied to bpf or bpf-next tree? 159----------------------------------------------------------------------- 160A: It means that the patch looks good for mainline inclusion from 161a BPF point of view. 162 163Be aware that this is not a final verdict that the patch will 164automatically get accepted into net or net-next trees eventually: 165 166On the bpf kernel mailing list reviews can come in at any point 167in time. If discussions around a patch conclude that they cannot 168get included as-is, we will either apply a follow-up fix or drop 169them from the trees entirely. Therefore, we also reserve to rebase 170the trees when deemed necessary. After all, the purpose of the tree 171is to: 172 173i) accumulate and stage BPF patches for integration into trees 174 like net and net-next, and 175 176ii) run extensive BPF test suite and 177 workloads on the patches before they make their way any further. 178 179Once the BPF pull request was accepted by David S. Miller, then 180the patches end up in net or net-next tree, respectively, and 181make their way from there further into mainline. Again, see the 182:ref:`netdev-FAQ` for additional information e.g. on how often they are 183merged to mainline. 184 185Q: How long do I need to wait for feedback on my BPF patches? 186------------------------------------------------------------- 187A: We try to keep the latency low. The usual time to feedback will 188be around 2 or 3 business days. It may vary depending on the 189complexity of changes and current patch load. 190 191Q: How often do you send pull requests to major kernel trees like net or net-next? 192---------------------------------------------------------------------------------- 193 194A: Pull requests will be sent out rather often in order to not 195accumulate too many patches in bpf or bpf-next. 196 197As a rule of thumb, expect pull requests for each tree regularly 198at the end of the week. In some cases pull requests could additionally 199come also in the middle of the week depending on the current patch 200load or urgency. 201 202Q: Are patches applied to bpf-next when the merge window is open? 203----------------------------------------------------------------- 204A: For the time when the merge window is open, bpf-next will not be 205processed. This is roughly analogous to net-next patch processing, 206so feel free to read up on the :ref:`netdev-FAQ` about further details. 207 208During those two weeks of merge window, we might ask you to resend 209your patch series once bpf-next is open again. Once Linus released 210a ``v*-rc1`` after the merge window, we continue processing of bpf-next. 211 212For non-subscribers to kernel mailing lists, there is also a status 213page run by David S. Miller on net-next that provides guidance: 214 215 http://vger.kernel.org/~davem/net-next.html 216 217Q: Verifier changes and test cases 218---------------------------------- 219Q: I made a BPF verifier change, do I need to add test cases for 220BPF kernel selftests_? 221 222A: If the patch has changes to the behavior of the verifier, then yes, 223it is absolutely necessary to add test cases to the BPF kernel 224selftests_ suite. If they are not present and we think they are 225needed, then we might ask for them before accepting any changes. 226 227In particular, test_verifier.c is tracking a high number of BPF test 228cases, including a lot of corner cases that LLVM BPF back end may 229generate out of the restricted C code. Thus, adding test cases is 230absolutely crucial to make sure future changes do not accidentally 231affect prior use-cases. Thus, treat those test cases as: verifier 232behavior that is not tracked in test_verifier.c could potentially 233be subject to change. 234 235Q: samples/bpf preference vs selftests? 236--------------------------------------- 237Q: When should I add code to ``samples/bpf/`` and when to BPF kernel 238selftests_? 239 240A: In general, we prefer additions to BPF kernel selftests_ rather than 241``samples/bpf/``. The rationale is very simple: kernel selftests are 242regularly run by various bots to test for kernel regressions. 243 244The more test cases we add to BPF selftests, the better the coverage 245and the less likely it is that those could accidentally break. It is 246not that BPF kernel selftests cannot demo how a specific feature can 247be used. 248 249That said, ``samples/bpf/`` may be a good place for people to get started, 250so it might be advisable that simple demos of features could go into 251``samples/bpf/``, but advanced functional and corner-case testing rather 252into kernel selftests. 253 254If your sample looks like a test case, then go for BPF kernel selftests 255instead! 256 257Q: When should I add code to the bpftool? 258----------------------------------------- 259A: The main purpose of bpftool (under tools/bpf/bpftool/) is to provide 260a central user space tool for debugging and introspection of BPF programs 261and maps that are active in the kernel. If UAPI changes related to BPF 262enable for dumping additional information of programs or maps, then 263bpftool should be extended as well to support dumping them. 264 265Q: When should I add code to iproute2's BPF loader? 266--------------------------------------------------- 267A: For UAPI changes related to the XDP or tc layer (e.g. ``cls_bpf``), 268the convention is that those control-path related changes are added to 269iproute2's BPF loader as well from user space side. This is not only 270useful to have UAPI changes properly designed to be usable, but also 271to make those changes available to a wider user base of major 272downstream distributions. 273 274Q: Do you accept patches as well for iproute2's BPF loader? 275----------------------------------------------------------- 276A: Patches for the iproute2's BPF loader have to be sent to: 277 278 netdev@vger.kernel.org 279 280While those patches are not processed by the BPF kernel maintainers, 281please keep them in Cc as well, so they can be reviewed. 282 283The official git repository for iproute2 is run by Stephen Hemminger 284and can be found at: 285 286 https://git.kernel.org/pub/scm/linux/kernel/git/shemminger/iproute2.git/ 287 288The patches need to have a subject prefix of '``[PATCH iproute2 289master]``' or '``[PATCH iproute2 net-next]``'. '``master``' or 290'``net-next``' describes the target branch where the patch should be 291applied to. Meaning, if kernel changes went into the net-next kernel 292tree, then the related iproute2 changes need to go into the iproute2 293net-next branch, otherwise they can be targeted at master branch. The 294iproute2 net-next branch will get merged into the master branch after 295the current iproute2 version from master has been released. 296 297Like BPF, the patches end up in patchwork under the netdev project and 298are delegated to 'shemminger' for further processing: 299 300 http://patchwork.ozlabs.org/project/netdev/list/?delegate=389 301 302Q: What is the minimum requirement before I submit my BPF patches? 303------------------------------------------------------------------ 304A: When submitting patches, always take the time and properly test your 305patches *prior* to submission. Never rush them! If maintainers find 306that your patches have not been properly tested, it is a good way to 307get them grumpy. Testing patch submissions is a hard requirement! 308 309Note, fixes that go to bpf tree *must* have a ``Fixes:`` tag included. 310The same applies to fixes that target bpf-next, where the affected 311commit is in net-next (or in some cases bpf-next). The ``Fixes:`` tag is 312crucial in order to identify follow-up commits and tremendously helps 313for people having to do backporting, so it is a must have! 314 315We also don't accept patches with an empty commit message. Take your 316time and properly write up a high quality commit message, it is 317essential! 318 319Think about it this way: other developers looking at your code a month 320from now need to understand *why* a certain change has been done that 321way, and whether there have been flaws in the analysis or assumptions 322that the original author did. Thus providing a proper rationale and 323describing the use-case for the changes is a must. 324 325Patch submissions with >1 patch must have a cover letter which includes 326a high level description of the series. This high level summary will 327then be placed into the merge commit by the BPF maintainers such that 328it is also accessible from the git log for future reference. 329 330Q: Features changing BPF JIT and/or LLVM 331---------------------------------------- 332Q: What do I need to consider when adding a new instruction or feature 333that would require BPF JIT and/or LLVM integration as well? 334 335A: We try hard to keep all BPF JITs up to date such that the same user 336experience can be guaranteed when running BPF programs on different 337architectures without having the program punt to the less efficient 338interpreter in case the in-kernel BPF JIT is enabled. 339 340If you are unable to implement or test the required JIT changes for 341certain architectures, please work together with the related BPF JIT 342developers in order to get the feature implemented in a timely manner. 343Please refer to the git log (``arch/*/net/``) to locate the necessary 344people for helping out. 345 346Also always make sure to add BPF test cases (e.g. test_bpf.c and 347test_verifier.c) for new instructions, so that they can receive 348broad test coverage and help run-time testing the various BPF JITs. 349 350In case of new BPF instructions, once the changes have been accepted 351into the Linux kernel, please implement support into LLVM's BPF back 352end. See LLVM_ section below for further information. 353 354Stable submission 355================= 356 357Q: I need a specific BPF commit in stable kernels. What should I do? 358-------------------------------------------------------------------- 359A: In case you need a specific fix in stable kernels, first check whether 360the commit has already been applied in the related ``linux-*.y`` branches: 361 362 https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/ 363 364If not the case, then drop an email to the BPF maintainers with the 365netdev kernel mailing list in Cc and ask for the fix to be queued up: 366 367 netdev@vger.kernel.org 368 369The process in general is the same as on netdev itself, see also the 370:ref:`netdev-FAQ`. 371 372Q: Do you also backport to kernels not currently maintained as stable? 373---------------------------------------------------------------------- 374A: No. If you need a specific BPF commit in kernels that are currently not 375maintained by the stable maintainers, then you are on your own. 376 377The current stable and longterm stable kernels are all listed here: 378 379 https://www.kernel.org/ 380 381Q: The BPF patch I am about to submit needs to go to stable as well 382------------------------------------------------------------------- 383What should I do? 384 385A: The same rules apply as with netdev patch submissions in general, see 386the :ref:`netdev-FAQ`. 387 388Never add "``Cc: stable@vger.kernel.org``" to the patch description, but 389ask the BPF maintainers to queue the patches instead. This can be done 390with a note, for example, under the ``---`` part of the patch which does 391not go into the git log. Alternatively, this can be done as a simple 392request by mail instead. 393 394Q: Queue stable patches 395----------------------- 396Q: Where do I find currently queued BPF patches that will be submitted 397to stable? 398 399A: Once patches that fix critical bugs got applied into the bpf tree, they 400are queued up for stable submission under: 401 402 http://patchwork.ozlabs.org/bundle/bpf/stable/?state=* 403 404They will be on hold there at minimum until the related commit made its 405way into the mainline kernel tree. 406 407After having been under broader exposure, the queued patches will be 408submitted by the BPF maintainers to the stable maintainers. 409 410Testing patches 411=============== 412 413Q: How to run BPF selftests 414--------------------------- 415A: After you have booted into the newly compiled kernel, navigate to 416the BPF selftests_ suite in order to test BPF functionality (current 417working directory points to the root of the cloned git tree):: 418 419 $ cd tools/testing/selftests/bpf/ 420 $ make 421 422To run the verifier tests:: 423 424 $ sudo ./test_verifier 425 426The verifier tests print out all the current checks being 427performed. The summary at the end of running all tests will dump 428information of test successes and failures:: 429 430 Summary: 418 PASSED, 0 FAILED 431 432In order to run through all BPF selftests, the following command is 433needed:: 434 435 $ sudo make run_tests 436 437See the kernels selftest `Documentation/dev-tools/kselftest.rst`_ 438document for further documentation. 439 440To maximize the number of tests passing, the .config of the kernel 441under test should match the config file fragment in 442tools/testing/selftests/bpf as closely as possible. 443 444Finally to ensure support for latest BPF Type Format features - 445discussed in `Documentation/bpf/btf.rst`_ - pahole version 1.16 446is required for kernels built with CONFIG_DEBUG_INFO_BTF=y. 447pahole is delivered in the dwarves package or can be built 448from source at 449 450https://github.com/acmel/dwarves 451 452pahole starts to use libbpf definitions and APIs since v1.13 after the 453commit 21507cd3e97b ("pahole: add libbpf as submodule under lib/bpf"). 454It works well with the git repository because the libbpf submodule will 455use "git submodule update --init --recursive" to update. 456 457Unfortunately, the default github release source code does not contain 458libbpf submodule source code and this will cause build issues, the tarball 459from https://git.kernel.org/pub/scm/devel/pahole/pahole.git/ is same with 460github, you can get the source tarball with corresponding libbpf submodule 461codes from 462 463https://fedorapeople.org/~acme/dwarves 464 465Some distros have pahole version 1.16 packaged already, e.g. 466Fedora, Gentoo. 467 468Q: Which BPF kernel selftests version should I run my kernel against? 469--------------------------------------------------------------------- 470A: If you run a kernel ``xyz``, then always run the BPF kernel selftests 471from that kernel ``xyz`` as well. Do not expect that the BPF selftest 472from the latest mainline tree will pass all the time. 473 474In particular, test_bpf.c and test_verifier.c have a large number of 475test cases and are constantly updated with new BPF test sequences, or 476existing ones are adapted to verifier changes e.g. due to verifier 477becoming smarter and being able to better track certain things. 478 479LLVM 480==== 481 482Q: Where do I find LLVM with BPF support? 483----------------------------------------- 484A: The BPF back end for LLVM is upstream in LLVM since version 3.7.1. 485 486All major distributions these days ship LLVM with BPF back end enabled, 487so for the majority of use-cases it is not required to compile LLVM by 488hand anymore, just install the distribution provided package. 489 490LLVM's static compiler lists the supported targets through 491``llc --version``, make sure BPF targets are listed. Example:: 492 493 $ llc --version 494 LLVM (http://llvm.org/): 495 LLVM version 10.0.0 496 Optimized build. 497 Default target: x86_64-unknown-linux-gnu 498 Host CPU: skylake 499 500 Registered Targets: 501 aarch64 - AArch64 (little endian) 502 bpf - BPF (host endian) 503 bpfeb - BPF (big endian) 504 bpfel - BPF (little endian) 505 x86 - 32-bit X86: Pentium-Pro and above 506 x86-64 - 64-bit X86: EM64T and AMD64 507 508For developers in order to utilize the latest features added to LLVM's 509BPF back end, it is advisable to run the latest LLVM releases. Support 510for new BPF kernel features such as additions to the BPF instruction 511set are often developed together. 512 513All LLVM releases can be found at: http://releases.llvm.org/ 514 515Q: Got it, so how do I build LLVM manually anyway? 516-------------------------------------------------- 517A: We recommend that developers who want the fastest incremental builds 518use the Ninja build system, you can find it in your system's package 519manager, usually the package is ninja or ninja-build. 520 521You need ninja, cmake and gcc-c++ as build requisites for LLVM. Once you 522have that set up, proceed with building the latest LLVM and clang version 523from the git repositories:: 524 525 $ git clone https://github.com/llvm/llvm-project.git 526 $ mkdir -p llvm-project/llvm/build 527 $ cd llvm-project/llvm/build 528 $ cmake .. -G "Ninja" -DLLVM_TARGETS_TO_BUILD="BPF;X86" \ 529 -DLLVM_ENABLE_PROJECTS="clang" \ 530 -DCMAKE_BUILD_TYPE=Release \ 531 -DLLVM_BUILD_RUNTIME=OFF 532 $ ninja 533 534The built binaries can then be found in the build/bin/ directory, where 535you can point the PATH variable to. 536 537Set ``-DLLVM_TARGETS_TO_BUILD`` equal to the target you wish to build, you 538will find a full list of targets within the llvm-project/llvm/lib/Target 539directory. 540 541Q: Reporting LLVM BPF issues 542---------------------------- 543Q: Should I notify BPF kernel maintainers about issues in LLVM's BPF code 544generation back end or about LLVM generated code that the verifier 545refuses to accept? 546 547A: Yes, please do! 548 549LLVM's BPF back end is a key piece of the whole BPF 550infrastructure and it ties deeply into verification of programs from the 551kernel side. Therefore, any issues on either side need to be investigated 552and fixed whenever necessary. 553 554Therefore, please make sure to bring them up at netdev kernel mailing 555list and Cc BPF maintainers for LLVM and kernel bits: 556 557* Yonghong Song <yhs@fb.com> 558* Alexei Starovoitov <ast@kernel.org> 559* Daniel Borkmann <daniel@iogearbox.net> 560 561LLVM also has an issue tracker where BPF related bugs can be found: 562 563 https://bugs.llvm.org/buglist.cgi?quicksearch=bpf 564 565However, it is better to reach out through mailing lists with having 566maintainers in Cc. 567 568Q: New BPF instruction for kernel and LLVM 569------------------------------------------ 570Q: I have added a new BPF instruction to the kernel, how can I integrate 571it into LLVM? 572 573A: LLVM has a ``-mcpu`` selector for the BPF back end in order to allow 574the selection of BPF instruction set extensions. By default the 575``generic`` processor target is used, which is the base instruction set 576(v1) of BPF. 577 578LLVM has an option to select ``-mcpu=probe`` where it will probe the host 579kernel for supported BPF instruction set extensions and selects the 580optimal set automatically. 581 582For cross-compilation, a specific version can be select manually as well :: 583 584 $ llc -march bpf -mcpu=help 585 Available CPUs for this target: 586 587 generic - Select the generic processor. 588 probe - Select the probe processor. 589 v1 - Select the v1 processor. 590 v2 - Select the v2 processor. 591 [...] 592 593Newly added BPF instructions to the Linux kernel need to follow the same 594scheme, bump the instruction set version and implement probing for the 595extensions such that ``-mcpu=probe`` users can benefit from the 596optimization transparently when upgrading their kernels. 597 598If you are unable to implement support for the newly added BPF instruction 599please reach out to BPF developers for help. 600 601By the way, the BPF kernel selftests run with ``-mcpu=probe`` for better 602test coverage. 603 604Q: clang flag for target bpf? 605----------------------------- 606Q: In some cases clang flag ``-target bpf`` is used but in other cases the 607default clang target, which matches the underlying architecture, is used. 608What is the difference and when I should use which? 609 610A: Although LLVM IR generation and optimization try to stay architecture 611independent, ``-target <arch>`` still has some impact on generated code: 612 613- BPF program may recursively include header file(s) with file scope 614 inline assembly codes. The default target can handle this well, 615 while ``bpf`` target may fail if bpf backend assembler does not 616 understand these assembly codes, which is true in most cases. 617 618- When compiled without ``-g``, additional elf sections, e.g., 619 .eh_frame and .rela.eh_frame, may be present in the object file 620 with default target, but not with ``bpf`` target. 621 622- The default target may turn a C switch statement into a switch table 623 lookup and jump operation. Since the switch table is placed 624 in the global readonly section, the bpf program will fail to load. 625 The bpf target does not support switch table optimization. 626 The clang option ``-fno-jump-tables`` can be used to disable 627 switch table generation. 628 629- For clang ``-target bpf``, it is guaranteed that pointer or long / 630 unsigned long types will always have a width of 64 bit, no matter 631 whether underlying clang binary or default target (or kernel) is 632 32 bit. However, when native clang target is used, then it will 633 compile these types based on the underlying architecture's conventions, 634 meaning in case of 32 bit architecture, pointer or long / unsigned 635 long types e.g. in BPF context structure will have width of 32 bit 636 while the BPF LLVM back end still operates in 64 bit. The native 637 target is mostly needed in tracing for the case of walking ``pt_regs`` 638 or other kernel structures where CPU's register width matters. 639 Otherwise, ``clang -target bpf`` is generally recommended. 640 641You should use default target when: 642 643- Your program includes a header file, e.g., ptrace.h, which eventually 644 pulls in some header files containing file scope host assembly codes. 645 646- You can add ``-fno-jump-tables`` to work around the switch table issue. 647 648Otherwise, you can use ``bpf`` target. Additionally, you *must* use bpf target 649when: 650 651- Your program uses data structures with pointer or long / unsigned long 652 types that interface with BPF helpers or context data structures. Access 653 into these structures is verified by the BPF verifier and may result 654 in verification failures if the native architecture is not aligned with 655 the BPF architecture, e.g. 64-bit. An example of this is 656 BPF_PROG_TYPE_SK_MSG require ``-target bpf`` 657 658 659.. Links 660.. _Documentation/process/: https://www.kernel.org/doc/html/latest/process/ 661.. _netdev-FAQ: Documentation/process/maintainer-netdev.rst 662.. _selftests: 663 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/bpf/ 664.. _Documentation/dev-tools/kselftest.rst: 665 https://www.kernel.org/doc/html/latest/dev-tools/kselftest.html 666.. _Documentation/bpf/btf.rst: btf.rst 667 668Happy BPF hacking! 669