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Thu, 6 Aug 2026 17:18:29 +0000 (GMT) Message-ID: <401c45c9-c37d-4151-8aa9-70fc6d09ea25@linux.ibm.com> Date: Thu, 6 Aug 2026 22:48:28 +0530 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 2/8] powerpc/bpf: Move out dummy_tramp_addr after Long branch stub 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-Info: AW1haW4tMjYwODA2MDEzNSBTYWx0ZWRfXxFHV2YK2bqLg BupiEsiRFMUYiN9SK8UyeJexxIqp95SXGE8vWRiMwyTI9K3EkGL6oyVytaqJjC+r6/hyB8fQTZB Wltc140nQA/CsiQ4Av3auv4KfT8dZKE= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODA2MDEzNSBTYWx0ZWRfX3QSLug0S9agk eazWX3OBpJX/aqWYJgz0tNJAAuBHx53oUv8qx9InDIf8+xiJaTkYJDA9YixuZ5Jcbi4+n9WlEgy oTy2jKF3oTflZNbIM4rwinX2NnSdRTmh60MRcQJJB6eYG402ziyU05jDCVkj8w98Z//Vu7T41Da SBwR38B620HBB4b40JLGQxRj5O9CNqEoUBg3FkfFY5tdnnT8HA1BJaXxeJxWebxGQlfo0FF1Riv 2nhTtJebEJj/YkXR8RGi7ftfzly0wx/j3EoB+CulYAcIdHJl0eDPGj2s6C7tqPXgeXowMv7hZmm 0NvFYoBCNQAxrpX8NLzoXj3UIPCMkgKiPiSosm9+B/wiUXmU0upogoYlCnKG16ti2MfMv/xOec+ BUvP/vnjwkP2THmZvHC8T7HscEmMmy/+BKbaAsCS2k9liENWurWYJyUqZFgK7Nqhc2QawIT45wq IraEx4rlqG5kVHFquJQ== X-Authority-Analysis: v=2.4 cv=SI1ykuvH c=1 sm=1 tr=0 ts=6a74c1ee cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VnNF1IyMAAAA:8 a=PG8nOvWyLKg_aLjP1-sA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: YBoWjp8NYG8pbjCUyw_VP3VTSZVaawTr X-Proofpoint-GUID: YBoWjp8NYG8pbjCUyw_VP3VTSZVaawTr 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 clxscore=1011 bulkscore=0 suspectscore=0 impostorscore=0 spamscore=0 phishscore=0 priorityscore=1501 lowpriorityscore=0 adultscore=0 malwarescore=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 > > Move the long branch address field to the bottom of the long > branch stub. This allows uninterrupted disassembly until the > last 8 bytes. The last bytes exclusion is logically necessary to Instead of "last 8 bytes", should be "last 4/8 bytes" > prevent disassembly failure, otherwise the actual program layout > is never altered. Hence no effect on overall program size. > 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. > > Fixes: d243b62b7bd3 ("powerpc64/bpf: Add support for bpf trampolines") > Signed-off-by: Abhishek Dubey > Signed-off-by: Saket Kumar Bhaskar > Tested-by: Yeswanth Krishna Tellakula > --- > arch/powerpc/net/bpf_jit.h | 3 +- > arch/powerpc/net/bpf_jit_comp.c | 51 ++++++++++++++++--------------- > arch/powerpc/net/bpf_jit_comp32.c | 3 +- > arch/powerpc/net/bpf_jit_comp64.c | 3 +- > 4 files changed, 33 insertions(+), 27 deletions(-) > > diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h > index 71e6e7d01057..6632de9871dd 100644 > --- a/arch/powerpc/net/bpf_jit.h > +++ b/arch/powerpc/net/bpf_jit.h > @@ -217,7 +217,8 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx); > void bpf_jit_build_epilogue(u32 *image, u32 *fimage, struct codegen_context *ctx); > void bpf_jit_build_fentry_stubs(u32 *image, u32 *fimage, struct codegen_context *ctx); > void bpf_jit_realloc_regs(struct codegen_context *ctx); > -int bpf_jit_emit_exit_insn(u32 *image, struct codegen_context *ctx, int tmp_reg, long exit_addr); > +int bpf_jit_emit_exit_insn(u32 *image, u32 *fimage, struct codegen_context *ctx, int tmp_reg, > + long exit_addr); This function prototype change, the corresponding call site updates & the second parameter update in bpf_jit_build_epilogue() call inside bpf_jit_emit_exit_insn() function belong in the previous patch... > void prepare_for_fsession_fentry(u32 *image, struct codegen_context *ctx, int cookie_cnt, > int cookie_off, int retval_off); > void store_func_meta(u32 *image, struct codegen_context *ctx, u64 func_meta, int func_meta_off); > diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c > index 42046f73c279..5d559d613f3a 100644 > --- a/arch/powerpc/net/bpf_jit_comp.c > +++ b/arch/powerpc/net/bpf_jit_comp.c > @@ -52,9 +52,10 @@ asm ( > void bpf_jit_build_fentry_stubs(u32 *image, u32 *fimage, struct codegen_context *ctx) > { > int ool_stub_idx, long_branch_stub_idx; > - int ool_stub_sz; > + int stub_sz; > > /* > + * The dummy_tramp_addr field is placed at bottom of Long branch stub. > * 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. > @@ -62,13 +63,10 @@ void bpf_jit_build_fentry_stubs(u32 *image, u32 *fimage, struct codegen_context > * dummy_tramp_addr must be 8-byte aligned for load-register > * compatibility. The fimage can be non 8-byte aligned, so final > * alignment depends on start of fimage and the stub's instruction > - * count offset. The OOL stub size is 4 instructions (with > - * CONFIG_PPC_FTRACE_OUT_OF_LINE) or 3 instructions (without) > - * before dummy_tramp_addr. > - * > - * Emit a NOP here if (ctx->idx + ool_stub_sz) is odd, so that > - * dummy_tramp_addr lands at an even instruction offset (== 8-byte > - * aligned from an 8-byte aligned base). > + * count. The stubs block has 11 instructions (with > + * CONFIG_PPC_FTRACE_OUT_OF_LINE) or 10 instructions (without) > + * before dummy_tramp_addr field. Emit a NOP if the address of > + * dummy_tramp_addr is non aligned. > * > * In pass=0 when image==NULL, conservatively account for space > * required to accommodate alignment NOP. In case final pass skips > @@ -76,8 +74,8 @@ void bpf_jit_build_fentry_stubs(u32 *image, u32 *fimage, struct codegen_context > * jited_len signifies correct program size. > */ > > - ool_stub_sz = IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE) ? 16 : 12; > - if (!image || !IS_ALIGNED((unsigned long)fimage + ctx->idx*4 + ool_stub_sz, SZL)) > + stub_sz = IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE) ? 44 : 40; > + if (!image || !IS_ALIGNED((unsigned long)fimage + ctx->idx*4 + stub_sz, SZL)) > EMIT(PPC_RAW_NOP()); > > /* > @@ -98,35 +96,37 @@ 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 Likewise, the comment should be: "SZL bytes 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; > } > } > > -int bpf_jit_emit_exit_insn(u32 *image, struct codegen_context *ctx, int tmp_reg, long exit_addr) > +int bpf_jit_emit_exit_insn(u32 *image, u32 *fimage, struct codegen_context *ctx, > + int tmp_reg, long exit_addr) > { > if (!exit_addr || is_offset_in_branch_range(exit_addr - (ctx->idx * 4))) { > PPC_JMP(exit_addr); > @@ -136,7 +136,7 @@ int bpf_jit_emit_exit_insn(u32 *image, struct codegen_context *ctx, int tmp_reg, > PPC_JMP(ctx->alt_exit_addr); > } else { > ctx->alt_exit_addr = ctx->idx * 4; > - bpf_jit_build_epilogue(image, NULL, ctx); > + bpf_jit_build_epilogue(image, fimage, ctx); > } > > return 0; > @@ -1294,6 +1294,7 @@ 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] / > @@ -1301,14 +1302,14 @@ 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. > * > @@ -1410,10 +1411,12 @@ 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) > diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c > index 95bda0dee925..f5b9441cf46a 100644 > --- a/arch/powerpc/net/bpf_jit_comp32.c > +++ b/arch/powerpc/net/bpf_jit_comp32.c > @@ -1149,7 +1149,8 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code > * we'll just fall through to the epilogue. > */ > if (i != flen - 1) { > - ret = bpf_jit_emit_exit_insn(image, ctx, _R0, exit_addr); > + ret = bpf_jit_emit_exit_insn(image, fimage, > + ctx, _R0, exit_addr); > if (ret) > return ret; > } > diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c > index ed78992f4dac..951eb10ca1f6 100644 > --- a/arch/powerpc/net/bpf_jit_comp64.c > +++ b/arch/powerpc/net/bpf_jit_comp64.c > @@ -1737,7 +1737,8 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code > * we'll just fall through to the epilogue. > */ > if (i != flen - 1) { > - ret = bpf_jit_emit_exit_insn(image, ctx, tmp1_reg, exit_addr); > + ret = bpf_jit_emit_exit_insn(image, fimage, ctx, > + tmp1_reg, exit_addr); > if (ret) > return ret; > } - Hari