[v2] Strict disable implicit fallthrough

[RFC PATCH v2 78/78] meson.build: increase -Wimplicit-fallthrough to 5

Emmanouil Pitsidianakis posted 78 patches 2 years, 2 months ago

Diff against v1 v3
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Maintainers: Richard Henderson <richard.henderson@linaro.org>, Paolo Bonzini <pbonzini@redhat.com>, Gerd Hoffmann <kraxel@redhat.com>, "Marc-André Lureau" <marcandre.lureau@redhat.com>, Christian Schoenebeck <qemu_oss@crudebyte.com>, John Snow <jsnow@redhat.com>, Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>, Kevin Wolf <kwolf@redhat.com>, Hanna Reitz <hreitz@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, Fam Zheng <fam@euphon.net>, Ronnie Sahlberg <ronniesahlberg@gmail.com>, Peter Lieven <pl@kamp.de>, Jeff Cody <codyprime@gmail.com>, Yuval Shaia <yuval.shaia.ml@gmail.com>, Marcel Apfelbaum <marcel.apfelbaum@gmail.com>, Raphael Norwitz <raphael.norwitz@nutanix.com>, "Michael S. Tsirkin" <mst@redhat.com>, Laurent Vivier <laurent@vivier.eu>, Yoshinori Sato <ysato@users.sourceforge.jp>, Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>, Artyom Tarasenko <atar4qemu@gmail.com>, "Alex Bennée" <alex.bennee@linaro.org>, "Daniel P. Berrangé" <berrange@redhat.com>, Thomas Huth <thuth@redhat.com>, Markus Armbruster <armbru@redhat.com>, "Philippe Mathieu-Daudé" <philmd@linaro.org>, Juan Quintela <quintela@redhat.com>, Aurelien Jarno <aurelien@aurel32.net>, Peter Maydell <peter.maydell@linaro.org>, Igor Mammedov <imammedo@redhat.com>, Ani Sinha <anisinha@redhat.com>, "Cédric Le Goater" <clg@kaod.org>, Andrew Jeffery <andrew@aj.id.au>, Joel Stanley <joel@jms.id.au>, Alistair Francis <alistair@alistair23.me>, "Edgar E. Iglesias" <edgar.iglesias@gmail.com>, Eric Auger <eric.auger@redhat.com>, Stefano Stabellini <sstabellini@kernel.org>, Anthony Perard <anthony.perard@citrix.com>, Paul Durrant <paul@xen.org>, Jonathan Cameron <jonathan.cameron@huawei.com>, Fan Ni <fan.ni@samsung.com>, Peter Xu <peterx@redhat.com>, Jason Wang <jasowang@redhat.com>, Eduardo Habkost <eduardo@habkost.net>, David Woodhouse <dwmw2@infradead.org>, Corey Minyard <minyard@acm.org>, Paul Burton <paulburton@kernel.org>, Aleksandar Rikalo <aleksandar.rikalo@syrmia.com>, Pavel Pisa <pisa@cmp.felk.cvut.cz>, Vikram Garhwal <fnu.vikram@xilinx.com>, Akihiko Odaki <akihiko.odaki@daynix.com>, Sriram Yagnaraman <sriram.yagnaraman@est.tech>, Dmitry Fleytman <dmitry.fleytman@gmail.com>, Keith Busch <kbusch@kernel.org>, Klaus Jensen <its@irrelevant.dk>, Nicholas Piggin <npiggin@gmail.com>, "Frédéric Barrat" <fbarrat@linux.ibm.com>, Huai-Cheng Kuo <hchkuo@avery-design.com.tw>, Chris Browy <cbrowy@avery-design.com>, Daniel Henrique Barboza <danielhb413@gmail.com>, David Gibson <david@gibson.dropbear.id.au>, Harsh Prateek Bora <harshpb@linux.ibm.com>, Christian Borntraeger <borntraeger@linux.ibm.com>, David Hildenbrand <david@redhat.com>, Ilya Leoshkevich <iii@linux.ibm.com>, Halil Pasic <pasic@linux.ibm.com>, Eric Farman <farman@linux.ibm.com>, Matthew Rosato <mjrosato@linux.ibm.com>, Hannes Reinecke <hare@suse.com>, Bin Meng <bin.meng@windriver.com>, Tyrone Ting <kfting@nuvoton.com>, Hao Wu <wuhaotsh@google.com>, Magnus Damm <magnus.damm@gmail.com>, Fabiano Rosas <farosas@suse.de>, Leonardo Bras <leobras@redhat.com>, Eric Blake <eblake@redhat.com>, Michael Roth <michael.roth@amd.com>, Konstantin Kostiuk <kkostiuk@redhat.com>, Michael Rolnik <mrolnik@gmail.com>, Alessandro Di Federico <ale@rev.ng>, Anton Johansson <anjo@rev.ng>, Cameron Esfahani <dirty@apple.com>, Roman Bolshakov <rbolshakov@ddn.com>, Marcelo Tosatti <mtosatti@redhat.com>, Song Gao <gaosong@loongson.cn>, Huacai Chen <chenhuacai@kernel.org>, Jiaxun Yang <jiaxun.yang@flygoat.com>, Chris Wulff <crwulff@gmail.com>, Marek Vasut <marex@denx.de>, Stafford Horne <shorne@gmail.com>, Palmer Dabbelt <palmer@dabbelt.com>, Weiwei Li <liweiwei@iscas.ac.cn>, Liu Zhiwei <zhiwei_liu@linux.alibaba.com>, Bastian Koppelmann <kbastian@mail.uni-paderborn.de>, Max Filippov <jcmvbkbc@gmail.com>, WANG Xuerui <git@xen0n.name>, Stefan Weil <sw@weilnetz.de>

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[RFC PATCH v2 78/78] meson.build: increase -Wimplicit-fallthrough to 5

Posted by Emmanouil Pitsidianakis 2 years, 2 months ago

Make GCC's implicit fall-through static analysis stricter by requiring
the use of the fallthrough attribute statement instead of comments.

This makes the QEMU code style more consistent.

Signed-off-by: Emmanouil Pitsidianakis <manos.pitsidianakis@linaro.org>
---
 docs/devel/style.rst | 23 +++++++++++++++++++++++
 meson.build          |  2 +-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/docs/devel/style.rst b/docs/devel/style.rst
index 2f68b50079..f473dd24e9 100644
--- a/docs/devel/style.rst
+++ b/docs/devel/style.rst
@@ -612,28 +612,51 @@ While this generally results in simpler, less leak-prone code, there
 are still some caveats to beware of
 
 * Variables declared with g_auto* MUST always be initialized,
   otherwise the cleanup function will use uninitialized stack memory
 
 * If a variable declared with g_auto* holds a value which must
   live beyond the life of the function, that value must be saved
   and the original variable NULL'd out. This can be simpler using
   g_steal_pointer
 
 
 .. code-block:: c
 
     char *somefunc(void)
     {
         g_autofree char *foo = g_strdup_printf("foo%", "wibble");
         g_autoptr (GList) bar = .....
 
         if (eek) {
            return NULL;
         }
 
         return g_steal_pointer(&foo);
     }
 
+Implicit switch case fall-through
+=================================
+
+The C language allows switch cases to "fall-through" when a "break" statement
+is missing at the end of a case. This, however, introduces ambiguity in the
+code, as it's not always clear if the missing break is intentional or a bug.
+
+As this behaviour allows for bugs we do not allow "implicit fall-through".
+
+In order to identify intentional fall-through cases, we have adopted a
+pseudo-keyword macro 'fallthrough' which expands to gcc's extension
+__attribute__((__fallthrough__)).  `Statement Attributes
+<https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html>`_
+
+All switch/case blocks must end in one of:
+
+.. code-block:: c
+
+	  break;
+	  fallthrough;
+	  continue;
+	  goto <label>;
+	  return [expression];
 
 QEMU Specific Idioms
 ********************
diff --git a/meson.build b/meson.build
index 79aef19bdc..e8805f0e0c 100644
--- a/meson.build
+++ b/meson.build
@@ -438,28 +438,28 @@ add_global_link_arguments(qemu_ldflags, native: false, language: all_languages)
 warn_flags = [
   '-Wundef',
   '-Wwrite-strings',
   '-Wmissing-prototypes',
   '-Wstrict-prototypes',
   '-Wredundant-decls',
   '-Wold-style-declaration',
   '-Wold-style-definition',
   '-Wtype-limits',
   '-Wformat-security',
   '-Wformat-y2k',
   '-Winit-self',
   '-Wignored-qualifiers',
   '-Wempty-body',
   '-Wnested-externs',
   '-Wendif-labels',
   '-Wexpansion-to-defined',
-  '-Wimplicit-fallthrough=2',
+  '-Wimplicit-fallthrough=5',
   '-Wmissing-format-attribute',
   '-Wno-initializer-overrides',
   '-Wno-missing-include-dirs',
   '-Wno-shift-negative-value',
   '-Wno-string-plus-int',
   '-Wno-typedef-redefinition',
   '-Wno-tautological-type-limit-compare',
   '-Wno-psabi',
   '-Wno-gnu-variable-sized-type-not-at-end',
 ]
-- 
2.39.2