On Thu, Aug 06, 2026 at 11:04:04PM +0530, Hari Bathini wrote: > > > On 05/08/26 11:36 am, Saket Kumar Bhaskar wrote: > > From: Abhishek Dubey <[email protected]> > > > > 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 <dummy_tramp_addr> <---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 <dummy_tramp_addr>" (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/[email protected] > > > > 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/[email protected] > > [v2]: > > https://lore.kernel.org/bpf/[email protected] > > [v3]: > > https://lore.kernel.org/bpf/[email protected] > > [v4]: > > https://lore.kernel.org/bpf/[email protected] > > [v5]: > > https://lore.kernel.org/bpf/[email protected] > > [v6]: > > https://lore.kernel.org/bpf/[email protected] > > [v7]: > > https://lore.kernel.org/bpf/[email protected] > > [v8]: > > https://lore.kernel.org/bpf/[email protected] > > [v9]: > > https://lore.kernel.org/bpf/[email protected]/ > > > > 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 I have sent the v11 for this series https://lore.kernel.org/all/27ec08c30f6c37b3f25ba735f9cd7f81ff9e98d5.1786099877.git.sk...@linux.ibm.com/
- Saket
