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Sun, 17 May 2026 17:40:32 +0000 (GMT) Received: from ltcrain4-lp15.ltc.tadn.ibm.com (unknown [9.5.7.39]) by smtpav01.fra02v.mail.ibm.com (Postfix) with ESMTP; Sun, 17 May 2026 17:40:32 +0000 (GMT) From: adubey@linux.ibm.com To: bpf@vger.kernel.org Cc: hbathini@linux.ibm.com, linuxppc-dev@lists.ozlabs.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 v4 2/5] powerpc/bpf: Move out dummy_tramp_addr after Long branch stub Date: Sun, 17 May 2026 17:40:40 -0400 Message-ID: <20260517214043.12975-3-adubey@linux.ibm.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260517214043.12975-1-adubey@linux.ibm.com> References: <20260517214043.12975-1-adubey@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTE3MDE5MCBTYWx0ZWRfX9l+4PWBPteBG BCZxGx7+4ZPmn++XrQx85+vGP8/ZImSaq5dfBrgIJYWHiIR1wnUpZmyeDQmgJNYG87GLGrKDxUL 7LIn3p6DtJezAjTuKyHV4TfZqYcsdLdGdk8qE49oL1ZwJoNz3fII4y5HZuX2wHg9iH2IjCHG9UF zHqVwFYiQCBeTRxBacuFzFG9t5VrxXuBM1x/xNCY6KQ/z+ZaOFcWqKplOoXhVFtHK/VwEBqRQPE nhL/O9oXDiifc/YU5ndUUP3PXWD9f4B5Mmn/tdBv26GSYKlheQjBqZRLXGauXFr65ftHY772n8l n95XR++P3+ODl65yNQCtXDzS9BltRIgZ3CFANxTSVuoUtyp2j42p1n96OGw64G4EoJrapXjnUm3 OzM6DCNWR+2otfYZ84q0stSiYbWn5oyt+D5sUpeq6U35IsWrflj/9V+jV05HdS+dFSnWLabNmHK nlBkTCwCttmDYzW0jrQ== X-Authority-Analysis: v=2.4 cv=Np/htcdJ c=1 sm=1 tr=0 ts=6a09fd96 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VnNF1IyMAAAA:8 a=wRVbdlKoTiVShp7l6ZUA:9 X-Proofpoint-ORIG-GUID: GMXbFFkoZqifqBIlzu_vBcp5tjwetRu8 X-Proofpoint-GUID: GMXbFFkoZqifqBIlzu_vBcp5tjwetRu8 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=2026-05-17_04,2026-05-15_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 spamscore=0 clxscore=1015 priorityscore=1501 impostorscore=0 lowpriorityscore=0 suspectscore=0 adultscore=0 phishscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605130000 definitions=main-2605170190 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 | 34 +++++++++++++++++++-------------- 1 file changed, 20 insertions(+), 14 deletions(-) diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c index ef7614177cb1..b73bc9295c31 100644 --- a/arch/powerpc/net/bpf_jit_comp.c +++ b/arch/powerpc/net/bpf_jit_comp.c @@ -57,19 +57,21 @@ void bpf_jit_build_fentry_stubs(u32 *image, u32 *fimage, struct codegen_context * In the final pass, align the mis-aligned dummy_tramp_addr field * in the fimage. The alignment NOP must appear before OOL stub, * to make ool_stub_idx & long_branch_stub_idx constant from end. + * + * The dummy_tramp_addr field is placed at bottom of Long branch stub. */ #ifdef CONFIG_PPC64 if (fimage && image) { /* * pc points to first instruction of OOL stub, - * dummy_tramp_addr is past 4/3 instructions depending on + * dummy_tramp_addr is past 11/10 instructions depending on * CONFIG_PPC_FTRACE_OUT_OF_LINE is enabled/not respectively. * * The decision to emit alignment NOP must depend on the alignment * of dummy_tramp_addr field. */ unsigned long pc = (unsigned long)fimage + CTX_NIA(ctx); - pc += IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE) ? 4 : 3; + pc += IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE) ? 11 : 10; if (!IS_ALIGNED(pc, 8)) EMIT(PPC_RAW_NOP()); @@ -93,28 +95,29 @@ 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,$+4 - * mflr r12 - * ld r12, -8-SZL(r12) + * mflr r12 // lr/r12 stores pc of current(this) inst. + * ld r12, 20(r12) // offset(dummy_tramp_addr) from prev inst. is 20 * mtctr r12 - * mtlr r11 // needed to retain ftrace ABI + * mtlr r11 // needed to retain ftrace ABI * bctr + * .long // 8-byte aligned */ - if (image) - *((unsigned long *)&image[ctx->idx]) = (unsigned long)dummy_tramp; - - ctx->idx += SZL / 4; long_branch_stub_idx = ctx->idx; EMIT(PPC_RAW_MFLR(_R11)); EMIT(PPC_RAW_BCL4()); EMIT(PPC_RAW_MFLR(_R12)); - EMIT(PPC_RAW_LL(_R12, _R12, -8-SZL)); + EMIT(PPC_RAW_LL(_R12, _R12, 20)); EMIT(PPC_RAW_MTCTR(_R12)); EMIT(PPC_RAW_MTLR(_R11)); EMIT(PPC_RAW_BCTR()); + if (image) + *((unsigned long *)&image[ctx->idx]) = (unsigned long)dummy_tramp; + + ctx->idx += SZL / 4; + if (!bpf_jit_ool_stub) { bpf_jit_ool_stub = (ctx->idx - ool_stub_idx) * 4; bpf_jit_long_branch_stub = (ctx->idx - long_branch_stub_idx) * 4; @@ -1284,6 +1287,7 @@ static void do_isync(void *info __maybe_unused) * bpf_func: * [nop|b] ool_stub * 2. Out-of-line stub: + * nop // optional nop for alignment * ool_stub: * mflr r0 * [b|bl] / @@ -1291,14 +1295,14 @@ static void do_isync(void *info __maybe_unused) * b bpf_func + 4 * 3. Long branch stub: * long_branch_stub: - * .long / * mflr r11 * bcl 20,31,$+4 * mflr r12 - * ld r12, -16(r12) + * ld r12, 20(r12) * mtctr r12 * mtlr r11 // needed to retain ftrace ABI * bctr + * .long / * * dummy_tramp is used to reduce synchronization requirements. * @@ -1400,10 +1404,12 @@ 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