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AJvYcCWC+ynTrKfQ4SAB1T5PbKA0f9fFSbfcn8xGhKxR2uV8Za+61l/lQs0o9DhB8DXWlQRUyAeGabVNXDb6vOmd9J91ZFLifRRm16Nd7crSrG9UN1NO X-Gm-Message-State: AOJu0Yz0eZPbZswbCpujDtn7K7fUq4LMaLThGn8e1l9EE8WIV6doeDTd Ftajg6EfiR9cjW9y17EDtNu8jgZTn2GpvVrT9Qc9IERzMZRzBz5YuRZTSSB5knxn2Gjtw8x8ze2 eW01hfuDLJB+4aLy9puKfLVvU2J1jqPjo61G1 X-Google-Smtp-Source: AGHT+IFVRbRtTK93+JswPYwn75sDfz6NqIQ9pLfPvYXf2GKGX5xRtCwHXsSI1NF/q7+RSh2ICglMKo8eb6X0v/DUYE8= X-Received: by 2002:a05:6402:5d1:b0:566:b09e:80c4 with SMTP id n17-20020a05640205d100b00566b09e80c4mr242572edx.19.1710894654186; Tue, 19 Mar 2024 17:30:54 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20240319-tracing-fully-silence-wstring-compare-v1-0-81adb44403f5@kernel.org> <20240319-tracing-fully-silence-wstring-compare-v1-2-81adb44403f5@kernel.org> In-Reply-To: <20240319-tracing-fully-silence-wstring-compare-v1-2-81adb44403f5@kernel.org> From: Justin Stitt Date: Tue, 19 Mar 2024 17:30:41 -0700 Message-ID: Subject: Re: [PATCH 2/2] tracing: Ignore -Wstring-compare with diagnostic macros To: Nathan Chancellor Cc: rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, ndesaulniers@google.com, morbo@google.com, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, llvm@lists.linux.dev, patches@lists.linux.dev, Linux Kernel Functional Testing Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, Mar 19, 2024 at 9:08=E2=80=AFAM Nathan Chancellor wrote: > > Commit b1afefa62ca9 ("tracing: Use strcmp() in __assign_str() WARN_ON() > check") addressed a clang warning, -Wstring-compare, with the use of > __builtin_constant_p() to dispatch to strcmp() if the source string is a > string literal and a direct comparison if not. Unfortunately, even with > this change, the warning is still present because __builtin_constant_p() > is not evaluated at this stage of the pipeline, so clang still thinks > the else branch could occur for this situation: > > include/trace/events/sunrpc.h:705:4: error: result of comparison agains= t a string literal is unspecified (use an explicit string comparison functi= on instead) [-Werror,-Wstring-compare] > ... > include/trace/stages/stage6_event_callback.h:40:15: note: expanded from= macro '__assign_str' > 40 | (src) !=3D __data_offsets.dst##_pt= r_); \ > | ^ > ... > > Use the compiler diagnostic macros to disable this warning around the > WARN_ON_ONCE() expression since a string comparison function, strcmp(), > will always be used for the comparison of string literals. > > Fixes: b1afefa62ca9 ("tracing: Use strcmp() in __assign_str() WARN_ON() c= heck") > Reported-by: Linux Kernel Functional Testing > Closes: https://lore.kernel.org/all/CA+G9fYs=3DOTKAZS6g1P1Ewadfr0qoe6LgOV= SohqkXmFXotEODdg@mail.gmail.com/ > Signed-off-by: Nathan Chancellor > --- > include/trace/stages/stage6_event_callback.h | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/include/trace/stages/stage6_event_callback.h b/include/trace= /stages/stage6_event_callback.h > index 83da83a0c14f..56a4eea5a48e 100644 > --- a/include/trace/stages/stage6_event_callback.h > +++ b/include/trace/stages/stage6_event_callback.h > @@ -35,9 +35,14 @@ > do { \ > char *__str__ =3D __get_str(dst); = \ > int __len__ =3D __get_dynamic_array_len(dst) - 1; = \ > + __diag_push(); \ > + __diag_ignore(clang, 11, "-Wstring-compare", \ > + "__builtin_constant_p() ensures strcmp()" \ > + "will be used for string literals"); \ > WARN_ON_ONCE(__builtin_constant_p(src) ? \ > strcmp((src), __data_offsets.dst##_ptr_) : \ > (src) !=3D __data_offsets.dst##_ptr_); = \ What exactly is the point of the literal string comparison? Why doesn't strcmp do the trick? > + __diag_pop(); \ > memcpy(__str__, __data_offsets.dst##_ptr_ ? : \ > EVENT_NULL_STR, __len__); \ > __str__[__len__] =3D '\0'; = \ > > -- > 2.44.0 >