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From: Masahiro Yamada <masahiroy@kernel.org>
To: Arnd Bergmann <arnd@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Nicolas Schier <nicolas@fjasle.eu>,
	Guenter Roeck <linux@roeck-us.net>, Lee Jones <lee@kernel.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	linux-kbuild@vger.kernel.org, linux-arch@vger.kernel.org
Subject: Re: [PATCH 4/9] extrawarn: don't turn off -Wshift-negative-value for gcc-9
Date: Sat, 12 Aug 2023 21:04:35 +0900	[thread overview]
Message-ID: <CAK7LNASfNM9D=U_SjG5FoOy-=rrGKCRUJS_RB-XFa7oTpEuy-g@mail.gmail.com> (raw)
In-Reply-To: <20230811140327.3754597-5-arnd@kernel.org>

On Sat, Aug 12, 2023 at 5:00 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> The warning does nothing for newer versions of gcc since -fno-strict-overflow
> is used, on old versions it warns about lines that would be undefined
> otherwise:
>
> fs/isofs/util.c: In function 'iso_date':
> fs/isofs/util.c:40:14: error: left shift of negative value [-Werror=shift-negative-value]
>     tz |= (-1 << 8);
>               ^~
> drivers/video/fbdev/tdfxfb.c: In function 'tdfxfb_probe':
> drivers/video/fbdev/tdfxfb.c:1482:17: error: left shift of negative value [-Werror=shift-negative-value]
>       (PAGE_MASK << 1);
>                  ^~
> drivers/tty/serial/8250/8250_core.c: In function 'serial8250_request_rsa_resource':
> drivers/tty/serial/8250/8250_core.c:350:38: error: left shift of negative value [-Werror=shift-negative-value]
>   unsigned long start = UART_RSA_BASE << up->port.regshift;
>                                       ^~
> drivers/tty/serial/8250/8250_core.c: In function 'serial8250_release_rsa_resource':
> drivers/tty/serial/8250/8250_core.c:371:39: error: left shift of negative value [-Werror=shift-negative-value]
>   unsigned long offset = UART_RSA_BASE << up->port.regshift;
>                                        ^~
> drivers/clk/mvebu/dove-divider.c: In function 'dove_set_clock':
> drivers/clk/mvebu/dove-divider.c:145:14: error: left shift of negative value [-Werror=shift-negative-value]
>   mask = ~(~0 << dc->div_bit_size) << dc->div_bit_start;
>               ^~
> drivers/block/drbd/drbd_main.c: In function 'dcbp_set_pad_bits':
> drivers/block/drbd/drbd_main.c:1098:37: error: left shift of negative value [-Werror=shift-negative-value]
>   p->encoding = (p->encoding & (~0x7 << 4)) | (n << 4);
>
> Disable these conditionally to keep the command line a little shorter.



Just a nit for the commit subject and description.

It mentions only gcc, but also affects clang.




Is the following a better subject?

  extrawarn: don't turn off -Wshift-negative-value for gcc-9+ or clang

or

  extrawarn: turn off -Wshift-negative-value only for gcc < 9






-- 
Best Regards
Masahiro Yamada

  reply	other threads:[~2023-08-12 12:05 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-08-11 14:03 [PATCH 0/9] Kbuild: warning options cleanup and more warnings Arnd Bergmann
2023-08-11 14:03 ` [PATCH 1/9] Kbuild: only pass -fno-inline-functions-called-once for gcc Arnd Bergmann
2023-08-11 14:14   ` Nathan Chancellor
2023-08-11 14:23     ` Arnd Bergmann
2023-08-11 14:03 ` [PATCH 2/9] Kbuild: consolidate warning flags in scripts/Makefile.extrawarn Arnd Bergmann
2023-08-11 14:19   ` Nathan Chancellor
2023-08-11 14:26     ` Arnd Bergmann
2023-08-12  7:21       ` Masahiro Yamada
2023-08-20  1:36       ` Masahiro Yamada
2023-08-11 14:03 ` [PATCH 3/9] Kbuild: avoid duplicate warning options Arnd Bergmann
2023-08-12  9:21   ` Masahiro Yamada
2023-08-12  9:28     ` Arnd Bergmann
2023-08-20  1:38       ` Masahiro Yamada
2023-08-11 14:03 ` [PATCH 4/9] extrawarn: don't turn off -Wshift-negative-value for gcc-9 Arnd Bergmann
2023-08-12 12:04   ` Masahiro Yamada [this message]
2023-08-11 14:03 ` [PATCH 5/9] extrawarn: enable format and stringop overflow warnings in W=1 Arnd Bergmann
2023-08-12 13:10   ` Masahiro Yamada
2023-08-20  1:40     ` Masahiro Yamada
2023-08-21 18:26     ` Nick Desaulniers
2023-08-11 14:03 ` [PATCH 6/9] extrawarn: move -Wrestrict into W=1 warnings Arnd Bergmann
2023-08-12 13:20   ` Masahiro Yamada
2023-08-20  1:45   ` Masahiro Yamada
2023-08-11 14:03 ` [PATCH 7/9] extrawarn: do not disable -Wmain at W=1 level Arnd Bergmann
2023-08-11 14:03 ` [PATCH 8/9] extrawarn: enable more warnings in W=2 Arnd Bergmann
2023-08-11 14:03 ` [PATCH 9/9] [RFC] extrawarn: enable more W=1 warnings by default Arnd Bergmann
2023-08-11 16:09   ` Nathan Chancellor
2023-08-11 18:23     ` Arnd Bergmann
2023-08-14 19:52       ` Nathan Chancellor

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