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Tue, 25 Jul 2023 00:59:43 +0000 (GMT) Received: from ozlabs.au.ibm.com (unknown [9.192.253.14]) by smtpav05.fra02v.mail.ibm.com (Postfix) with ESMTP for ; Tue, 25 Jul 2023 00:59:43 +0000 (GMT) Received: from bgray-lenovo-p15.ozlabs.ibm.com (haven.au.ibm.com [9.192.254.114]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.au.ibm.com (Postfix) with ESMTPSA id 4133760459; Tue, 25 Jul 2023 10:59:41 +1000 (AEST) From: Benjamin Gray To: linuxppc-dev@lists.ozlabs.org Subject: [PATCH v1 4/4] selftests/powerpc/ptrace: Declare test temporary variables as volatile Date: Tue, 25 Jul 2023 10:58:41 +1000 Message-ID: <20230725005841.28854-5-bgray@linux.ibm.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230725005841.28854-1-bgray@linux.ibm.com> References: <20230725005841.28854-1-bgray@linux.ibm.com> MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: a6NehXqoA-lnRhnE72OJ9_2d7TUNstcL X-Proofpoint-ORIG-GUID: a6NehXqoA-lnRhnE72OJ9_2d7TUNstcL X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.957,Hydra:6.0.591,FMLib:17.11.176.26 definitions=2023-07-24_18,2023-07-24_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 mlxscore=0 lowpriorityscore=0 suspectscore=0 mlxlogscore=999 phishscore=0 malwarescore=0 adultscore=0 clxscore=1015 bulkscore=0 impostorscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2306200000 definitions=main-2307250003 X-Mailman-Approved-At: Tue, 25 Jul 2023 11:33:14 +1000 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Benjamin Gray Errors-To: linuxppc-dev-bounces+incoming=patchwork.ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" While the target is volatile, the temporary variables used to access the target cast away the volatile. This is undefined behaviour, and a compiler may optimise away/reorder these accesses, breaking the test. This was observed with GCC 13.1.1, but it can be difficult to reproduce because of the dependency on compiler behaviour. Signed-off-by: Benjamin Gray --- .../selftests/powerpc/ptrace/ptrace-hwbreak.c | 24 +++++++++---------- 1 file changed, 12 insertions(+), 12 deletions(-) diff --git a/tools/testing/selftests/powerpc/ptrace/ptrace-hwbreak.c b/tools/testing/selftests/powerpc/ptrace/ptrace-hwbreak.c index a16239277a6f..75d30d61ab0e 100644 --- a/tools/testing/selftests/powerpc/ptrace/ptrace-hwbreak.c +++ b/tools/testing/selftests/powerpc/ptrace/ptrace-hwbreak.c @@ -64,26 +64,26 @@ static bool dawr_present(struct ppc_debug_info *dbginfo) static void write_var(int len) { - __u8 *pcvar; - __u16 *psvar; - __u32 *pivar; - __u64 *plvar; + volatile __u8 *pcvar; + volatile __u16 *psvar; + volatile __u32 *pivar; + volatile __u64 *plvar; switch (len) { case 1: - pcvar = (__u8 *)&glvar; + pcvar = (volatile __u8 *)&glvar; *pcvar = 0xff; break; case 2: - psvar = (__u16 *)&glvar; + psvar = (volatile __u16 *)&glvar; *psvar = 0xffff; break; case 4: - pivar = (__u32 *)&glvar; + pivar = (volatile __u32 *)&glvar; *pivar = 0xffffffff; break; case 8: - plvar = (__u64 *)&glvar; + plvar = (volatile __u64 *)&glvar; *plvar = 0xffffffffffffffffLL; break; } @@ -98,16 +98,16 @@ static void read_var(int len) switch (len) { case 1: - cvar = (__u8)glvar; + cvar = (volatile __u8)glvar; break; case 2: - svar = (__u16)glvar; + svar = (volatile __u16)glvar; break; case 4: - ivar = (__u32)glvar; + ivar = (volatile __u32)glvar; break; case 8: - lvar = (__u64)glvar; + lvar = (volatile __u64)glvar; break; } }