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Thu, 6 Aug 2026 17:34:05 +0000 (GMT) Message-ID: <7ffaff94-b1b1-4420-8c19-c88bf49139a6@linux.ibm.com> Date: Thu, 6 Aug 2026 23:04:04 +0530 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 0/8] powerpc/bpf: address missing verifier selftest coverage To: Saket Kumar Bhaskar , bpf@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Cc: maddy@linux.ibm.com, ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net, shuah@kernel.org, linux-kselftest@vger.kernel.org, stable@vger.kernel.org, venkat88@linux.ibm.com, yeswanth@linux.ibm.com References: Content-Language: en-US From: Hari Bathini In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODA2MDEzNSBTYWx0ZWRfXz0eNHxrKCAc2 7cOhZVc+1Hu1K+QrowKkBPRJG6AYAfbPSM3pBCLVJyQ098ky35dTaQxfkN3cB25PbAwIqS+NSGu LeW2ByIzVBViSSPFOK4X1J1RBPaWgTaySYrXpuRcSx+2yJR8htNMuDN/PhL5NGyhHum2NINpxGq LzUeLNtIoKor/zwHWqk1HkwC4wcAkP0qRALHg6jYKc4q8bm4yF8u6OypxEr2Rer74xQYFco313O c+Gm9UZW5AnfTbjTYym3jxs4B96UPHaMXTk8RP+jL8lp+9OTMJxlZEC86pZhcfnvnkMruqQ7xoO B/h3aCYg0oEJZFO/CLzV8iuW4UH7+y+hRn7Y3jzaGTEm5sk1hvz0TFjXdABkAJT+05CFtPPKlL0 q4LQZWxZGK43eAJRDOIvgsyFYQXR+Ncnw7mKzKQZGtpJJbnZZ2/Tw1gi3oa/g9XZ74cQSn/riiI 8ddAGn0XkZwmjSRVTTg== X-Authority-Analysis: v=2.4 cv=WIFPmHsR c=1 sm=1 tr=0 ts=6a74c595 cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=NMmoX83GTePcWBc1ta0A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: _Xtn6_qUWWmjqDQQUIo7Lke3hwJsnIl8 X-Proofpoint-ORIG-GUID: _Xtn6_qUWWmjqDQQUIo7Lke3hwJsnIl8 X-Proofpoint-Spam-Info: AW1haW4tMjYwODA2MDEzNSBTYWx0ZWRfX99dOJ0yZek9n I5WiDTwTXmWWBtBXEBnwwIfdj8DzejCXgjF2f6oD4L/fuHW9sxrX9dVJtSwh5OkLmBDq61UUHfr i0Iskqd3b9NYRiuYz5lbeFGuDFDgUNE= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-06_01,2026-08-06_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 lowpriorityscore=0 priorityscore=1501 phishscore=0 malwarescore=0 suspectscore=0 clxscore=1015 impostorscore=0 bulkscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608060135 On 05/08/26 11:36 am, Saket Kumar Bhaskar wrote: > From: Abhishek Dubey > > The verifier selftest validates JITed instructions by matching expected > disassembly output. The first two patches fix issues in powerpc instruction > disassembly that were causing test flow failures. The fix is common for > 64-bit & 32-bit powerpc. Add support for the powerpc-specific "__powerpc64" > architecture tag in the third patch, enabling proper test filtering in > verifier test files. Introduce verifier testcases for tailcalls on powerpc64. > > The first patch in series is fix patch, correcting memory alignment with > 8-byte boundary for long branch address field. The subsequent patches > enables verifier selftests on powerpc. The fifth patch in the series fixes > incorrect comparator usage for comparing tailcall info with tailcall > threshold. The last two patches fix JIT buffer overflow for large BPF progs > and private stack memory leak (identified by bot during reviews). > > Issue Details: > -------------- > > The Long branch stub in the trampoline implementation[1] provides > flexibility to handles short as well as long branch distance to > actual trampoline. Whereas, the 8 bytes long dummy_tramp_addr field > sitting before long branch stub leads to failure when enabling > verifier based seltest for ppc64. > > The verifier selftests require disassembing the final jited image > to get native instructions. Later the disassembled instruction > sequence is matched against sequence of instructions provided in > test-file under __jited() wrapper. The final jited image contains > Out-of-line stub and Long branch stub as part of epilogue jitting > for a bpf program. The 8 bytes space for dummy_tramp is sandwiched > between both above mentioned stubs. These 8 bytes contain memory > address of dummy trampoline during trampoline invocation which don't > correspond to any powerpc instructions. So, disassembly fails > resulting in failure of verifier selftests. > > The following code snippet shows the problem with current arrangement > made for dummy_tramp_addr. > > /* Out-of-line stub */ > mflr r0 > [b|bl] tramp > mtlr r0 //only with OOL > b bpf_func + 4 > /* Long branch stub */ > .long <---Invalid bytes sequence, disassembly fails > mflr r11 > bcl 20,31,$+4 > mflr r12 > ld r12, -8-SZL(r12) > mtctr r12 > mtlr r11 //retain ftrace ABI > bctr > > Consider test program binary of size 112 bytes: > 0: 00000060 10004de8 00002039 f8ff21f9 81ff21f8 7000e1fb 3000e13b > 28: 3000e13b 2a006038 f8ff7ff8 00000039 7000e1eb 80002138 7843037d > 56: 2000804e a602087c 00000060 a603087c bcffff4b c0341d00 000000c0 > 84: a602687d 05009f42 a602887d f0ff8ce9 a603897d a603687d 2004804e > > Disassembly output of above binary for ppc64le: > pc:0 left:112 00 00 00 60 : nop > pc:4 left:108 10 00 4d e8 : ld 2, 16(13) > pc:8 left:104 00 00 20 39 : li 9, 0 > pc:12 left:100 f8 ff 21 f9 : std 9, -8(1) > pc:16 left:96 81 ff 21 f8 : stdu 1, -128(1) > pc:20 left:92 70 00 e1 fb : std 31, 112(1) > pc:24 left:88 30 00 e1 3b : addi 31, 1, 48 > pc:28 left:84 30 00 e1 3b : addi 31, 1, 48 > pc:32 left:80 2a 00 60 38 : li 3, 42 > pc:36 left:76 f8 ff 7f f8 : std 3, -8(31) > pc:40 left:72 00 00 00 39 : li 8, 0 > pc:44 left:68 70 00 e1 eb : ld 31, 112(1) > pc:48 left:64 80 00 21 38 : addi 1, 1, 128 > pc:52 left:60 78 43 03 7d : mr 3, 8 > pc:56 left:56 20 00 80 4e : blr > pc:60 left:52 a6 02 08 7c : mflr 0 > pc:64 left:48 00 00 00 60 : nop > pc:68 left:44 a6 03 08 7c : mtlr 0 > pc:72 left:40 bc ff ff 4b : b .-68 > pc:76 left:36 c0 34 1d 00 : > ... > > Failure log: > Can't disasm instruction at offset 76: c0 34 1d 00 00 00 00 c0 a6 02 68 7d 05 00 9f 42 > -------------------------------------- > > Observation: > Can't disasm instruction at offset 76 as this address has > ".long " (0xc0341d00000000c0) > But valid instructions follow at offset 84 onwards. > > Move the long branch address space to the bottom of the long > branch stub. This allows uninterrupted disassembly until the > last 8 bytes. Exclude these last bytes from the overall > program length to prevent failure in assembly generation. > > Following is disassembler output for same test program with moved down > dummy_tramp_addr field: > ..... > ..... > pc:68 left:44 a6 03 08 7c : mtlr 0 > pc:72 left:40 bc ff ff 4b : b .-68 > pc:76 left:36 a6 02 68 7d : mflr 11 > pc:80 left:32 05 00 9f 42 : bcl 20, 31, .+4 > pc:84 left:28 a6 02 88 7d : mflr 12 > pc:88 left:24 14 00 8c e9 : ld 12, 20(12) > pc:92 left:20 a6 03 89 7d : mtctr 12 > pc:96 left:16 a6 03 68 7d : mtlr 11 > pc:100 left:12 20 04 80 4e : bctr > pc:104 left:8 c0 34 1d 00 : > > Failure log: > Can't disasm instruction at offset 104: c0 34 1d 00 00 00 00 c0 > --------------------------------------- > Disassembly logic can truncate at 104, ignoring last 8 bytes. > > Update the dummy_tramp_addr field offset calculation from the end > of the program to reflect its new location, for bpf_arch_text_poke() > to update the actual trampoline's address in this field. > > [1] https://lore.kernel.org/all/20241030070850.1361304-18-hbathini@linux.ibm.com > > v9->v10: > Modified expected JIT instruction in selftest for > CONFIG_PPC_KERNEL_PCREL incase of PPC_LI64 instruction. > Fix for stale entries in exception table > Update ARCH_POWERPC64 enum value to 0x40 to resolve rebase > conflict with ARCH_LOONGARCH (0x20). > > v8->v9: > Dynamic pass handling until code keeps shrinking > Fix private stack memory leak > > v7->v8: > Fixed bot identified issues of alt_exit_addr and BPF_EXIT > Fixed 32-bit ppc function signature mismatch > > v6->v7: > Fixed JIT buffer overflow in case of large BPF progs > Addressed remaining bot comments > > v5->v6: > Changed alignment NOP emittion dependency on fimage layout > Adjust tail truncate length for 32-bit ppc > Addressed few minor bot comments > > v4->v5: > Handled alignment NOP emit logic and corresponding stub offsets > Handled image buffer overflow problem in last pass > Above changes took care of other bot reviews > Included LLVMDisposeMessage() for graceful freeing > Adjusted parameters in bpf_jit_build_fentry_stubs for ppc32 > Adjusted expected JIT inst. in tailcall test for > CONFIG_PPC_KERNEL_PCREL config > Added fix patch at last for inaccurate use of cmplwi inst. > > v3->v4: > Changed logic for emitting alignment NOP > > v2->v3: > Removed fixed NOP from bottom of long branch stub > Rebased on top of bpf-next > > v1->v2: > Added fix-patch to correct memory alignment in-place > Moved the optional alignmnet NOP before OOL stub > > [v1]: https://lore.kernel.org/bpf/20260225013627.22098-1-adubey@linux.ibm.com > [v2]: https://lore.kernel.org/bpf/20260403004011.44417-1-adubey@linux.ibm.com > [v3]: https://lore.kernel.org/bpf/20260411221413.44304-1-adubey@linux.ibm.com > [v4]: https://lore.kernel.org/bpf/20260517214043.12975-1-adubey@linux.ibm.com > [v5]: https://lore.kernel.org/bpf/20260519233812.18787-1-adubey@linux.ibm.com > [v6]: https://lore.kernel.org/bpf/20260529015855.364704-1-adubey@linux.ibm.com > [v7]: https://lore.kernel.org/bpf/20260611153826.31187-1-adubey@linux.ibm.com > [v8]: https://lore.kernel.org/bpf/20260616164741.32252-1-adubey@linux.ibm.com > [v9]: https://lore.kernel.org/bpf/20260623231411.6216-1-adubey@linux.ibm.com/ > > Abhishek Dubey (8): > powerpc/bpf: fix alignment of long branch trampoline addres to t > powerpc/bpf: Move out dummy_tramp_addr after Long branch stub > selftest/bpf: Fixing powerpc JIT disassembly failure > selftest/bpf: Enable verifier selftest for powerpc64 > powerpc64/bpf: fix compare instruction emitted for tailcall > selftest/bpf: Add tailcall verifier selftest for powerpc64 > powerpc/bpf: fix buffer overflow in JIT for large BPF programs > powerpc64/bpf: fix percpu private stack leak on JIT failure > > arch/powerpc/net/bpf_jit.h | 20 +++- > arch/powerpc/net/bpf_jit_comp.c | 102 +++++++++++++----- > arch/powerpc/net/bpf_jit_comp32.c | 7 +- > arch/powerpc/net/bpf_jit_comp64.c | 15 +-- > .../selftests/bpf/jit_disasm_helpers.c | 25 ++++- > tools/testing/selftests/bpf/progs/bpf_misc.h | 1 + > .../bpf/progs/verifier_tailcall_jit.c | 74 +++++++++++++ > tools/testing/selftests/bpf/test_loader.c | 5 + > 8 files changed, 209 insertions(+), 40 deletions(-) > Alexei, Maddy, Given this has changes in common code too, should this go via bpf tree? If yes, @Saket can you post the next revision with bpf tag to make it explicit... - Hari