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Rao" , Mark Rutland , Daniel Borkmann , Masahiro Yamada , Nicholas Piggin , Alexei Starovoitov , Steven Rostedt , Andrii Nakryiko , Christophe Leroy , Vishal Chourasia , Mahesh J Salgaonkar , Masami Hiramatsu Subject: [PATCH v5 03/17] powerpc64/ftrace: Nop out additional 'std' instruction emitted by gcc v5.x Date: Mon, 16 Sep 2024 02:26:34 +0530 Message-ID: <20240915205648.830121-4-hbathini@linux.ibm.com> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20240915205648.830121-1-hbathini@linux.ibm.com> References: <20240915205648.830121-1-hbathini@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 X-Proofpoint-GUID: U65oGFEzZiVl3dL9IQtvh1YgrmEd-8zK X-Proofpoint-ORIG-GUID: iYVkRkamHpZtvuWs33JBpbHqaBTtYSDk X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.680,FMLib:17.12.60.29 definitions=2024-09-15_12,2024-09-13_02,2024-09-02_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 spamscore=0 malwarescore=0 bulkscore=0 phishscore=0 clxscore=1015 priorityscore=1501 mlxlogscore=960 suspectscore=0 impostorscore=0 mlxscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2408220000 definitions=main-2409150159 Content-Type: text/plain; charset="utf-8" From: Naveen N Rao Gcc v5.x emits a 3-instruction sequence for -mprofile-kernel: mflr r0 std r0, 16(r1) bl _mcount Gcc v6.x moved to a simpler 2-instruction sequence by removing the 'std' instruction. The store saved the return address in the LR save area in the caller stack frame for stack unwinding. However, with dynamic ftrace, we no longer have a call to _mcount on kernel boot when ftrace is not enabled. When ftrace is enabled, that store is performed within ftrace_caller(). As such, the additional 'std' instruction is redundant. Nop it out on kernel boot. With this change, we now use the same 2-instruction profiling sequence with both -mprofile-kernel, as well as -fpatchable-function-entry on 64-bit powerpc. Signed-off-by: Naveen N Rao --- arch/powerpc/kernel/trace/ftrace.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace= /ftrace.c index d8d6b4fd9a14..2ef504700e8d 100644 --- a/arch/powerpc/kernel/trace/ftrace.c +++ b/arch/powerpc/kernel/trace/ftrace.c @@ -246,8 +246,12 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftr= ace *rec) /* Expected sequence: 'mflr r0', ['std r0,16(r1)'], 'bl _mcount' */ ret =3D ftrace_read_inst(ip - 4, &old); if (!ret && !ppc_inst_equal(old, ppc_inst(PPC_RAW_MFLR(_R0)))) { + /* Gcc v5.x emit the additional 'std' instruction, gcc v6.x don't */ ret =3D ftrace_validate_inst(ip - 8, ppc_inst(PPC_RAW_MFLR(_R0))); - ret |=3D ftrace_validate_inst(ip - 4, ppc_inst(PPC_RAW_STD(_R0, _R1, 16= ))); + if (ret) + return ret; + ret =3D ftrace_modify_code(ip - 4, ppc_inst(PPC_RAW_STD(_R0, _R1, 16)), + ppc_inst(PPC_RAW_NOP())); } } else { return -EINVAL; --=20 2.46.0