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Thu, 2 Apr 2026 20:40:19 +0000 (GMT) From: adubey@linux.ibm.com To: linuxppc-dev@lists.ozlabs.org Cc: hbathini@linux.ibm.com, bpf@vger.kernel.org, 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, Abhishek Dubey Subject: [PATCH v2 2/5] powerpc/bpf: Move out dummy_tramp_addr after Long branch stub Date: Thu, 2 Apr 2026 20:40:08 -0400 Message-ID: <20260403004011.44417-3-adubey@linux.ibm.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260403004011.44417-1-adubey@linux.ibm.com> References: <20260403004011.44417-1-adubey@linux.ibm.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=Fdo6BZ+6 c=1 sm=1 tr=0 ts=69ced43b cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=A5OVakUREuEA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VnNF1IyMAAAA:8 a=2TgXZs7zRl4deLkxamQA:9 X-Proofpoint-ORIG-GUID: 5SRogSnlLtghnkEnHb7WE_NyNHuSCe_e X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDAyMDE4MSBTYWx0ZWRfX3oJhtaBEHr9K +JohFLncZ5w0k2RH3F9dYrzR8p+82ZAVhtg6DKsvsm3tkwfMy+GVykQ95S5OgLzsJe+z+lh+GUr N+1BmrnhITZBYTyBwvXzn4DU5+s4TuevDTUa+cmHEWzz63bU5ccv3JNyt4Na32ut6tRXZuuJiOJ gWhetz5mbWwhanXojubYhgsjr2+5D1YuS0vkB2qjMFva312Up3y/LIdVjrP7/LREacU2mKUhNju 1AvBFUprn0xCrpPyYSeAzGe/1qyx4Fd5LLf5ErhQfhDRKl+xpsgG3RPHKbImpj42JhcNMpomVN5 fv/V6JjkVkzjkAieWm73HToQzW26NzXnQIGAqCtvOVUFs3W2Ez0GOnJ2kGo5KEY47lnH5moTaXI FxNdCydQ80UAagaQyU35hscTlW7v4qu66n9Cf33XH2n5N7KqAj1fuPkZuE1x96LJI2+XOwX05HB jRKWjOJ2Av7BtjNKXcg== X-Proofpoint-GUID: 5SRogSnlLtghnkEnHb7WE_NyNHuSCe_e X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-04-02_03,2026-04-02_05,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 clxscore=1015 bulkscore=0 suspectscore=0 priorityscore=1501 adultscore=0 malwarescore=0 phishscore=0 spamscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2604020181 From: Abhishek Dubey 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. Also, align dummy_tramp_addr field with 8-byte boundary. Following is disassembler output for 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. All BPF trampoline selftests continue to pass with this patch applied. Signed-off-by: Abhishek Dubey --- arch/powerpc/net/bpf_jit_comp.c | 35 ++++++++++++++++++++++----------- 1 file changed, 24 insertions(+), 11 deletions(-) diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c index 3cbb3647f7a0..00abad48fa6c 100644 --- a/arch/powerpc/net/bpf_jit_comp.c +++ b/arch/powerpc/net/bpf_jit_comp.c @@ -93,27 +93,36 @@ void bpf_jit_build_fentry_stubs(u32 *image, u32 *fimage, struct codegen_context /* * Long branch stub: - * .long // 8-byte aligned * mflr r11 * bcl 20,31,$+4 - * mflr r12 - * ld r12, -8-SZL(r12) + * mflr r12 // lr/r12 stores current pc + * ld r12, 20(r12) // offset(dummy_tramp_addr) from prev inst. is 20 * mtctr r12 - * mtlr r11 // needed to retain ftrace ABI + * mtlr r11 // needed to retain ftrace ABI * bctr + * nop // for alignment of following address field + * .long // 8-byte aligned */ - if (image) - *((unsigned long *)&image[ctx->idx]) = (unsigned long)dummy_tramp; - - ctx->idx += SZL / 4; long_branch_stub_idx = ctx->idx; EMIT(PPC_RAW_MFLR(_R11)); EMIT(PPC_RAW_BCL4()); EMIT(PPC_RAW_MFLR(_R12)); - EMIT(PPC_RAW_LL(_R12, _R12, -8-SZL)); + EMIT(PPC_RAW_LL(_R12, _R12, 20)); EMIT(PPC_RAW_MTCTR(_R12)); EMIT(PPC_RAW_MTLR(_R11)); EMIT(PPC_RAW_BCTR()); + /* + * The start of Long branch stub is guaranteed to be aligned as + * result of optional NOP injection before OOL stub above. + * Append tail NOP to re-gain 8-byte alignment disturbed by odd + * instruction count in Long branch stub. + */ + EMIT(PPC_RAW_NOP()); + + if (image) + *((unsigned long *)&image[ctx->idx]) = (unsigned long)dummy_tramp; + + ctx->idx += SZL / 4; if (!bpf_jit_ool_stub) { bpf_jit_ool_stub = (ctx->idx - ool_stub_idx) * 4; @@ -1309,6 +1318,7 @@ static void do_isync(void *info __maybe_unused) * bpf_func: * [nop|b] ool_stub * 2. Out-of-line stub: + * nop // optional nop for alignment * ool_stub: * mflr r0 * [b|bl] / @@ -1316,7 +1326,6 @@ static void do_isync(void *info __maybe_unused) * b bpf_func + 4 * 3. Long branch stub: * long_branch_stub: - * .long / * mflr r11 * bcl 20,31,$+4 * mflr r12 @@ -1324,6 +1333,8 @@ static void do_isync(void *info __maybe_unused) * mtctr r12 * mtlr r11 // needed to retain ftrace ABI * bctr + * nop // nop for mem alignment of dummy_tramp_addr + * .long / * * dummy_tramp is used to reduce synchronization requirements. * @@ -1425,10 +1436,12 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type old_t, * 1. Update the address in the long branch stub: * If new_addr is out of range, we will have to use the long branch stub, so patch new_addr * here. Otherwise, revert to dummy_tramp, but only if we had patched old_addr here. + * + * dummy_tramp_addr moved to bottom of long branch stub. */ if ((new_addr && !is_offset_in_branch_range(new_addr - ip)) || (old_addr && !is_offset_in_branch_range(old_addr - ip))) - ret = patch_ulong((void *)(bpf_func_end - bpf_jit_long_branch_stub - SZL), + ret = patch_ulong((void *)(bpf_func_end - SZL), /* SZL: dummy_tramp_addr offset */ (new_addr && !is_offset_in_branch_range(new_addr - ip)) ? (unsigned long)new_addr : (unsigned long)dummy_tramp); if (ret) -- 2.52.0