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Sat, 17 Jan 2026 10:33:28 +0000 (GMT) Message-ID: <7c2b6544-8a40-418a-81d5-b74494a36944@linux.ibm.com> Date: Sat, 17 Jan 2026 16:03:27 +0530 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/6] powerpc64/bpf: Tailcall handling with trampolines To: adubey@linux.ibm.com, bpf@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Cc: sachinpb@linux.ibm.com, venkat88@linux.ibm.com, andrii@kernel.org, eddyz87@gmail.com, mykolal@fb.com, ast@kernel.org, daniel@iogearbox.net, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, christophe.leroy@csgroup.eu, naveen@kernel.org, maddy@linux.ibm.com, mpe@ellerman.id.au, npiggin@gmail.com, memxor@gmail.com, iii@linux.ibm.com, shuah@kernel.org References: <20260105105212.136645-1-adubey@linux.ibm.com> <20260105105212.136645-3-adubey@linux.ibm.com> Content-Language: en-US From: Hari Bathini In-Reply-To: <20260105105212.136645-3-adubey@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMTE3MDA4NCBTYWx0ZWRfXwfQVznBx6oy6 MuvGNjPyLKXQXbdIL2c7kq+kWBgf/j6PRXrpZIDcntlyK+KZkgGY3Vbi5pxra/d0V1CCZNomr4M H19dVc0L7DQhy0n4y3eeGN90BNh0ui8VePlfVIhQElhoglIrvrjvzP8tZQEFR1CwDnAuNdXHox7 U2yy/ZMllDAKN/W8igSbLZuce5VkaGf2nIW1oH20CE1EtcCvs3UVxMDoiWrW4sE0z1VTwxfbeaH 8kJOy0oyB7pvDbvjoT6FSHNIFkYtCsmU2MxDBmwKOGUbvQQ5IjGtd6MMtijC6Jzy4XcRz9Ig0k4 8L59be+9E/En6BJ+PPNoJbWVE7KjuhgYAQQua2fTnOXkTbwBiRpRf0qJBRMJSxfRxoUQD+BTL1w /V9stI15fJ7DIruewuULMSvDRh9V0kzCcAZV99dIY2MeXrRS4LkJEQDIx6T9CrKlbyxnyb3txhw y/UuBvHMM3Mz1PJJSgA== X-Authority-Analysis: v=2.4 cv=BpSQAIX5 c=1 sm=1 tr=0 ts=696b6584 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=vUbySO9Y5rIA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VnNF1IyMAAAA:8 a=v1dMKb2XkRFja0Z4mHIA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: Lv2punErfHDXv5-vECztRtoPeAYi2K7L X-Proofpoint-ORIG-GUID: KPye0R8VwpD9Tmf02LIm7x4Eqc6UrH0E X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2026-01-16_09,2026-01-15_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 bulkscore=0 clxscore=1015 adultscore=0 phishscore=0 malwarescore=0 impostorscore=0 suspectscore=0 priorityscore=1501 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2601150000 definitions=main-2601170084 On 05/01/26 4:22 pm, adubey@linux.ibm.com wrote: > From: Abhishek Dubey > > The trampoline mechanism sets up its own stack frame and > an additional dummy frame. We need to have additional JIT > instructions handling tailcall dereferencing in the > trampoline's context. > > We don't add the two stack frames pointed above, rather > add space for conventional 'non-volatile register save area' > and tail_call_info in trampoline's frame for ppc64. This > makes the trampoline's frame consistent with layout of all > other frames. > > Signed-off-by: Abhishek Dubey > --- > arch/powerpc/net/bpf_jit_comp.c | 48 ++++++++++++++++++++++++++++----- > 1 file changed, 42 insertions(+), 6 deletions(-) > > diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c > index 069a8822c30d..4aaa0a287a45 100644 > --- a/arch/powerpc/net/bpf_jit_comp.c > +++ b/arch/powerpc/net/bpf_jit_comp.c > @@ -606,15 +606,42 @@ static int invoke_bpf_mod_ret(u32 *image, u32 *ro_image, struct codegen_context > return 0; > } > > -static void bpf_trampoline_setup_tail_call_cnt(u32 *image, struct codegen_context *ctx, > - int func_frame_offset, int r4_off) > +/* > + * Refer the label 'Generated stack layout' in this file for actual stack > + * layout during trampoline invocation. > + * > + * Refer __arch_prepare_bpf_trampoline() for stack component details. > + * > + * The tailcall count/reference is present in caller's stack frame. Its required > + * to copy the content of tail_call_info before calling the actual function > + * to which the trampoline is attached. > + * > + */ > + > +static void bpf_trampoline_setup_tail_call_info(u32 *image, struct codegen_context *ctx, > + int func_frame_offset, > + int bpf_dummy_frame_size, int r4_off) > { > if (IS_ENABLED(CONFIG_PPC64)) { > /* See bpf_jit_stack_tailcallinfo_offset() */ > - int tailcallcnt_offset = 7 * 8; This offset update should be part of patch#1 - Hari