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Wed, 28 Jul 2021 21:25:55 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4C22AAE045; Wed, 28 Jul 2021 21:25:55 +0000 (GMT) Received: from vm.lan (unknown [9.145.77.113]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 28 Jul 2021 21:25:55 +0000 (GMT) From: Ilya Leoshkevich To: Steven Rostedt , Ingo Molnar Cc: linux-kernel@vger.kernel.org, Heiko Carstens , Sven Schnelle , Vasily Gorbik , linux-s390@vger.kernel.org, Ilya Leoshkevich Subject: [PATCH 1/2] ftrace: Introduce ftrace_need_init_nop() Date: Wed, 28 Jul 2021 23:25:45 +0200 Message-Id: <20210728212546.128248-2-iii@linux.ibm.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210728212546.128248-1-iii@linux.ibm.com> References: <20210728212546.128248-1-iii@linux.ibm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 4H6YnvIV8U5ZK8s8HaUBHT8TpYDmVQ0P X-Proofpoint-ORIG-GUID: l1xqRmQLSmwZLK6KInKr9z3mPlclVn6D X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.790 definitions=2021-07-28_10:2021-07-27,2021-07-28 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 phishscore=0 suspectscore=0 clxscore=1015 bulkscore=0 spamscore=0 malwarescore=0 adultscore=0 impostorscore=0 mlxscore=0 mlxlogscore=999 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2107280113 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Implementing live patching on s390 requires each function's prologue to contain a very special kind of nop, which gcc and clang don't generate. However, the current code assumes that if CC_USING_NOP_MCOUNT is defined, then whatever the compiler generates is good enough. Move the CC_USING_NOP_MCOUNT check into the new ftrace_need_init_nop() macro, that the architectures can override. An alternative solution is to disable using -mnop-mcount in the Makefile, however, this makes the build logic (even) more complicated and forces the arch-specific code to deal with the useless __fentry__ symbol. Signed-off-by: Ilya Leoshkevich --- include/linux/ftrace.h | 16 ++++++++++++++++ kernel/trace/ftrace.c | 4 ++-- 2 files changed, 18 insertions(+), 2 deletions(-) diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h index a69f363b61bf..f1ea8988a045 100644 --- a/include/linux/ftrace.h +++ b/include/linux/ftrace.h @@ -643,6 +643,22 @@ static inline int ftrace_disable_ftrace_graph_caller(void) { return 0; } extern int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr); +/** + * ftrace_need_init_nop - return whether nop call sites should be initialized + * + * Normally the compiler's -mnop-mcount generates suitable nops, so we don't + * need to call ftrace_init_nop() if the code is built with that flag. + * Architectures where this is not always the case may define their own + * condition. + * + * Return must be: + * 0 if ftrace_init_nop() should be called + * Nonzero if ftrace_init_nop() should not be called + */ + +#ifndef ftrace_need_init_nop +#define ftrace_need_init_nop() (!__is_defined(CC_USING_NOP_MCOUNT)) +#endif /** * ftrace_init_nop - initialize a nop call site diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 7b180f61e6d3..7efbc8aaf7f6 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -3100,6 +3100,7 @@ ops_references_rec(struct ftrace_ops *ops, struct dyn_ftrace *rec) static int ftrace_update_code(struct module *mod, struct ftrace_page *new_pgs) { + bool init_nop = ftrace_need_init_nop(); struct ftrace_page *pg; struct dyn_ftrace *p; u64 start, stop; @@ -3138,8 +3139,7 @@ static int ftrace_update_code(struct module *mod, struct ftrace_page *new_pgs) * Do the initial record conversion from mcount jump * to the NOP instructions. */ - if (!__is_defined(CC_USING_NOP_MCOUNT) && - !ftrace_nop_initialize(mod, p)) + if (init_nop && !ftrace_nop_initialize(mod, p)) break; update_cnt++; -- 2.31.1