{"id":2222432,"url":"http://patchwork.ozlabs.org/api/1.1/covers/2222432/?format=json","web_url":"http://patchwork.ozlabs.org/project/linuxppc-dev/cover/20260411221413.44304-1-adubey@linux.ibm.com/","project":{"id":2,"url":"http://patchwork.ozlabs.org/api/1.1/projects/2/?format=json","name":"Linux PPC development","link_name":"linuxppc-dev","list_id":"linuxppc-dev.lists.ozlabs.org","list_email":"linuxppc-dev@lists.ozlabs.org","web_url":"https://github.com/linuxppc/wiki/wiki","scm_url":"https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git","webscm_url":"https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/"},"msgid":"<20260411221413.44304-1-adubey@linux.ibm.com>","date":"2026-04-11T22:14:08","name":"[v3,0/5] powerpc/bpf: Add support for verifier selftest","submitter":{"id":88541,"url":"http://patchwork.ozlabs.org/api/1.1/people/88541/?format=json","name":"adubey","email":"adubey@linux.ibm.com"},"mbox":"http://patchwork.ozlabs.org/project/linuxppc-dev/cover/20260411221413.44304-1-adubey@linux.ibm.com/mbox/","series":[{"id":499569,"url":"http://patchwork.ozlabs.org/api/1.1/series/499569/?format=json","web_url":"http://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=499569","date":"2026-04-11T22:14:08","name":"powerpc/bpf: Add support for verifier selftest","version":3,"mbox":"http://patchwork.ozlabs.org/series/499569/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/covers/2222432/comments/","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linuxppc-dev@lists.ozlabs.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=ibm.com header.i=@ibm.com header.a=rsa-sha256\n header.s=pp1 header.b=eLvft3lV;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=lists.ozlabs.org\n (client-ip=2404:9400:21b9:f100::1; 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The first two patches fix issues in powerpc instruction\ndisassembly that were causing test flow failures. The fix is common for \n64-bit & 32-bit powerpc. Add support for the powerpc-specific \"__powerpc64\"\narchitecture tag in the third patch, enabling proper test filtering in\nverifier test files. Introduce verifier testcases for tailcalls on powerpc64\nin the final patch.\n\nThe first patch in series is fix patch, correcting memory alignment with\n8-byte boundary for long branch trampoline address. The subsequent\npatches enables verifier selftests on powerpc.\n\nIssue Details:\n--------------\n\n The Long branch stub in the trampoline implementation[1] provides\n flexibility to handles short as well as long branch distance to\n actual trampoline. Whereas, the 8 bytes long dummy_tramp_addr field\n sitting before long branch stub leads to failure when enabling\n verifier based seltest for ppc64.\n \n The verifier selftests require disassembing the final jited image\n to get native instructions. Later the disassembled instruction\n sequence is matched against sequence of instructions provided in\n test-file under __jited() wrapper. The final jited image contains\n Out-of-line stub and Long branch stub as part of epilogue jitting\n for a bpf program. The 8 bytes space for dummy_tramp is sandwiched\n between both above mentioned stubs. These 8 bytes contain memory\n address of dummy trampoline during trampoline invocation which don't\n correspond to any powerpc instructions. So, disassembly fails\n resulting in failure of verifier selftests.\n \n The following code snippet shows the problem with current arrangement\n made for dummy_tramp_addr.\n \n /* Out-of-line stub */\n mflr r0 \n [b|bl] tramp\n mtlr r0 //only with OOL \n b bpf_func + 4 \n /* Long branch stub */\n .long <---Invalid bytes sequence, disassembly fails\n mflr r11 \n bcl 20,31,$+4\n mflr r12 \n ld r12, -8-SZL(r12)\n mtctr r12 \n mtlr r11 //retain ftrace ABI \n bctr\n\n Consider test program binary of size 112 bytes:\n 0: 00000060 10004de8 00002039 f8ff21f9 81ff21f8 7000e1fb 3000e13b\n 28: 3000e13b 2a006038 f8ff7ff8 00000039 7000e1eb 80002138 7843037d\n 56: 2000804e a602087c 00000060 a603087c bcffff4b c0341d00 000000c0\n 84: a602687d 05009f42 a602887d f0ff8ce9 a603897d a603687d 2004804e\n\n Disassembly output of above binary for ppc64le:\n pc:0 left:112 00 00 00 60 : nop\n pc:4 left:108 10 00 4d e8 : ld 2, 16(13)\n pc:8 left:104 00 00 20 39 : li 9, 0\n pc:12 left:100 f8 ff 21 f9 : std 9, -8(1)\n pc:16 left:96 81 ff 21 f8 : stdu 1, -128(1)\n pc:20 left:92 70 00 e1 fb : std 31, 112(1)\n pc:24 left:88 30 00 e1 3b : addi 31, 1, 48\n pc:28 left:84 30 00 e1 3b : addi 31, 1, 48\n pc:32 left:80 2a 00 60 38 : li 3, 42\n pc:36 left:76 f8 ff 7f f8 : std 3, -8(31)\n pc:40 left:72 00 00 00 39 : li 8, 0\n pc:44 left:68 70 00 e1 eb : ld 31, 112(1)\n pc:48 left:64 80 00 21 38 : addi 1, 1, 128\n pc:52 left:60 78 43 03 7d : mr 3, 8\n pc:56 left:56 20 00 80 4e : blr\n pc:60 left:52 a6 02 08 7c : mflr 0\n pc:64 left:48 00 00 00 60 : nop\n pc:68 left:44 a6 03 08 7c : mtlr 0\n pc:72 left:40 bc ff ff 4b : b .-68\n pc:76 left:36 c0 34 1d 00 :\n ...\n\n Failure log:\n Can't disasm instruction at offset 76: c0 34 1d 00 00 00 00 c0 a6 02 68 7d 05 00 9f 42\n --------------------------------------\n\n Observation:\n Can't disasm instruction at offset 76 as this address has\n \".long \" (0xc0341d00000000c0)\n But valid instructions follow at offset 84 onwards.\n\n Move the long branch address space to the bottom of the long\n branch stub. This allows uninterrupted disassembly until the\n last 8 bytes. Exclude these last bytes from the overall\n program length to prevent failure in assembly generation.\n\n Following is disassembler output for same test program with moved down\n dummy_tramp_addr field:\n .....\n .....\n pc:68 left:44 a6 03 08 7c : mtlr 0\n pc:72 left:40 bc ff ff 4b : b .-68\n pc:76 left:36 a6 02 68 7d : mflr 11\n pc:80 left:32 05 00 9f 42 : bcl 20, 31, .+4\n pc:84 left:28 a6 02 88 7d : mflr 12\n pc:88 left:24 14 00 8c e9 : ld 12, 20(12)\n pc:92 left:20 a6 03 89 7d : mtctr 12\n pc:96 left:16 a6 03 68 7d : mtlr 11\n pc:100 left:12 20 04 80 4e : bctr\n pc:104 left:8 c0 34 1d 00 :\n\n Failure log:\n Can't disasm instruction at offset 104: c0 34 1d 00 00 00 00 c0\n ---------------------------------------\n Disassembly logic can truncate at 104, ignoring last 8 bytes.\n\n Update the dummy_tramp_addr field offset calculation from the end\n of the program to reflect its new location, for bpf_arch_text_poke()\n to update the actual trampoline's address in this field.\n\n [1] https://lore.kernel.org/all/20241030070850.1361304-18-hbathini@linux.ibm.com\n\nv2->v3:\n Removed fixed NOP from bottom of long branch stub\n Rebased on top of bpf-next\n\nv1->v2:\n Added fix-patch to correct memory alignment in-place\n Moved the optional alignmnet NOP before OOL stub\n\n[v1]: https://lore.kernel.org/bpf/20260225013627.22098-1-adubey@linux.ibm.com\n[v2]: https://lore.kernel.org/bpf/20260403004011.44417-1-adubey@linux.ibm.com\n\nAbhishek Dubey (5):\n powerpc/bpf: fix alignment of long branch trampoline address\n powerpc/bpf: Move out dummy_tramp_addr after Long branch stub\n selftest/bpf: Fixing powerpc JIT disassembly failure\n selftest/bpf: Enable verifier selftest for powerpc64\n selftest/bpf: Add tailcall verifier selftest for powerpc64\n\n arch/powerpc/net/bpf_jit.h | 4 +-\n arch/powerpc/net/bpf_jit_comp.c | 60 ++++++++++++----\n arch/powerpc/net/bpf_jit_comp64.c | 4 +-\n .../selftests/bpf/jit_disasm_helpers.c | 13 +++-\n tools/testing/selftests/bpf/progs/bpf_misc.h | 1 +\n .../bpf/progs/verifier_tailcall_jit.c | 69 +++++++++++++++++++\n tools/testing/selftests/bpf/test_loader.c | 5 ++\n 7 files changed, 136 insertions(+), 20 deletions(-)"}