From: "Måns Rullgård" <mans@mansr.com> To: Marc Gonzalez <marc_gonzalez@sigmadesigns.com> Cc: Guenter Roeck <linux@roeck-us.net>, Wim Van Sebroeck <wim@iguana.be>, <linux-watchdog@vger.kernel.org>, <linux-kernel@vger.kernel.org>, <linux-arm-kernel@lists.infradead.org>, Thibaud Cornic <thibaud_cornic@sigmadesigns.com>, Mark Rutland <mark.rutland@arm.com>, Uwe Kleine-Konig <u.kleine-koenig@pengutronix.de>, Arnd Bergmann <arnd@arndb.de> Subject: Re: [PATCH 56/62] watchdog: tangox_wdt: Convert to use device managed functions Date: Thu, 12 Jan 2017 11:24:03 +0000 [thread overview] Message-ID: <yw1xlgugldws.fsf@unicorn.mansr.com> (raw) In-Reply-To: <0f68aa11-161b-0435-ea0f-851432464bc1@sigmadesigns.com> (Marc Gonzalez's message of "Thu, 12 Jan 2017 10:44:07 +0100") Marc Gonzalez <marc_gonzalez@sigmadesigns.com> writes: >> So far we have a claim that a cast to a void * may somehow be different >> to a cast to a different pointer, if used as function argument, and that >> the behavior with such a cast may be undefined. In other words, you claim >> that a function implemented as, say, >> >> void func(int *var) {} >> >> might result in undefined behavior if some header file declares it as >> >> void func(void *); >> >> and it is called as >> >> int var; >> >> func(&var); >> >> That seems really far fetched to me. > > Thanks for giving me an opportunity to play the language lawyer :-) > > C99 6.3.2.3 sub-clause 8 states: > > "A pointer to a function of one type may be converted to a pointer to > a function of another type and back again; the result shall compare > equal to the original pointer. If a converted pointer is used to call > a function whose type is not compatible with the pointed-to type, the > behavior is undefined." > > So, the behavior is undefined, not when you cast clk_disable_unprepare, > but when clk_disable_unprepare is later called through the devres->action > function pointer. Only if the function types are incompatible. C99 6.7.5.3 subclause 15: For two function types to be compatible, both shall specify compatible return types. Moreover, the parameter type lists, if both are present, shall agree in the number of parameters and in use of the ellipsis terminator; corresponding parameters shall have compatible types. The question then is whether pointer to void and pointer to struct clk are compatible types. 6.7.5.1 subclause 2: For two pointer types to be compatible, both shall be identically qualified and both shall be pointers to compatible types. 6.2.5 subclause 27: A pointer to void shall have the same representation and alignment requirements as a pointer to a character type. 39) 39) The same representation and alignment requirements are meant to imply interchangeability as arguments to functions, return values from functions, and members of unions. 6.3.2.3 subclause 1: A pointer to void may be converted to or from a pointer to any incomplete or object type. >From what I can tell, the standard stops just short of declaring pointer to void compatible with other pointer types. > However, I agree that it will work as expected on typical platforms > (where all pointers are the same size, and the calling convention > treats all pointers the same). Yes, I don't see how it could possibly go wrong. -- Måns Rullgård
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From: mans@mansr.com (Måns Rullgård) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH 56/62] watchdog: tangox_wdt: Convert to use device managed functions Date: Thu, 12 Jan 2017 11:24:03 +0000 [thread overview] Message-ID: <yw1xlgugldws.fsf@unicorn.mansr.com> (raw) In-Reply-To: <0f68aa11-161b-0435-ea0f-851432464bc1@sigmadesigns.com> (Marc Gonzalez's message of "Thu, 12 Jan 2017 10:44:07 +0100") Marc Gonzalez <marc_gonzalez@sigmadesigns.com> writes: >> So far we have a claim that a cast to a void * may somehow be different >> to a cast to a different pointer, if used as function argument, and that >> the behavior with such a cast may be undefined. In other words, you claim >> that a function implemented as, say, >> >> void func(int *var) {} >> >> might result in undefined behavior if some header file declares it as >> >> void func(void *); >> >> and it is called as >> >> int var; >> >> func(&var); >> >> That seems really far fetched to me. > > Thanks for giving me an opportunity to play the language lawyer :-) > > C99 6.3.2.3 sub-clause 8 states: > > "A pointer to a function of one type may be converted to a pointer to > a function of another type and back again; the result shall compare > equal to the original pointer. If a converted pointer is used to call > a function whose type is not compatible with the pointed-to type, the > behavior is undefined." > > So, the behavior is undefined, not when you cast clk_disable_unprepare, > but when clk_disable_unprepare is later called through the devres->action > function pointer. Only if the function types are incompatible. C99 6.7.5.3 subclause 15: For two function types to be compatible, both shall specify compatible return types. Moreover, the parameter type lists, if both are present, shall agree in the number of parameters and in use of the ellipsis terminator; corresponding parameters shall have compatible types. The question then is whether pointer to void and pointer to struct clk are compatible types. 6.7.5.1 subclause 2: For two pointer types to be compatible, both shall be identically qualified and both shall be pointers to compatible types. 6.2.5 subclause 27: A pointer to void shall have the same representation and alignment requirements as a pointer to a character type. 39) 39) The same representation and alignment requirements are meant to imply interchangeability as arguments to functions, return values from functions, and members of unions. 6.3.2.3 subclause 1: A pointer to void may be converted to or from a pointer to any incomplete or object type. >From what I can tell, the standard stops just short of declaring pointer to void compatible with other pointer types. > However, I agree that it will work as expected on typical platforms > (where all pointers are the same size, and the calling convention > treats all pointers the same). Yes, I don't see how it could possibly go wrong. -- M?ns Rullg?rd
next prev parent reply other threads:[~2017-01-12 11:24 UTC|newest] Thread overview: 143+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-01-10 23:34 [PATCH 00/62] watchdog: Convert to use device managed functions Guenter Roeck 2017-01-10 23:34 ` [PATCH 01/62] watchdog: asm9260_wdt: Convert to use device managed functions and other improvements Guenter Roeck 2017-01-10 23:34 ` [PATCH 02/62] watchdog: aspeed_wdt: Convert to use device managed functions Guenter Roeck 2017-01-11 5:18 ` Joel Stanley 2017-01-10 23:34 ` [PATCH 03/62] watchdog: at91sam9_wdt: " Guenter Roeck 2017-01-10 23:34 ` [PATCH 04/62] watchdog: atlas7_wdt: Convert to use device managed functions and other improvements Guenter Roeck 2017-01-10 23:34 ` [PATCH 05/62] watchdog: bcm2835_wdt: " Guenter Roeck 2017-01-10 23:34 ` Guenter Roeck 2017-01-14 6:27 ` Eric Anholt 2017-01-14 6:27 ` Eric Anholt 2017-01-10 23:34 ` [PATCH 06/62] watchdog: bcm47xx_wdt: Convert to use device managed functions Guenter Roeck 2017-01-10 23:34 ` [PATCH 07/62] watchdog: bcm7038_wdt: Convert to use device managed functions and other improvements Guenter Roeck 2017-01-10 23:34 ` [PATCH 08/62] watchdog: bcm_kona_wdt: " Guenter Roeck 2017-01-10 23:34 ` [PATCH 09/62] watchdog: cadence_wdt: " Guenter Roeck 2017-01-10 23:34 ` [PATCH 10/62] watchdog: coh901327_wdt: Convert to use device managed functions Guenter Roeck 2017-01-10 23:34 ` Guenter Roeck 2017-01-11 15:48 ` Linus Walleij 2017-01-11 15:48 ` Linus Walleij 2017-01-11 15:48 ` Linus Walleij 2017-01-10 23:34 ` [PATCH 11/62] watchdog: da9052_wdt: " Guenter Roeck 2017-01-17 14:12 ` Adam Thomson 2017-01-10 23:34 ` [PATCH 12/62] watchdog: da9055_wdt: " Guenter Roeck 2017-01-17 13:58 ` Adam Thomson 2017-01-10 23:34 ` [PATCH 13/62] watchdog: da9062_wdt: " Guenter Roeck 2017-01-17 14:17 ` Adam Thomson 2017-01-10 23:34 ` [PATCH 14/62] watchdog: da9063_wdt: " Guenter Roeck 2017-01-17 14:19 ` Adam Thomson 2017-01-10 23:34 ` [PATCH 15/62] watchdog: davinci_wdt: Convert to use device managed functions and other improvements Guenter Roeck 2017-01-10 23:34 ` [PATCH 16/62] watchdog: digicolor_wdt: " Guenter Roeck 2017-01-10 23:34 ` Guenter Roeck 2017-01-12 11:47 ` Baruch Siach 2017-01-12 11:47 ` Baruch Siach 2017-01-10 23:34 ` [PATCH 17/62] watchdog: dw_wdt: Convert to use device managed functions Guenter Roeck 2017-01-10 23:34 ` [PATCH 18/62] watchdog: ep93xx_wdt: " Guenter Roeck 2017-01-10 23:34 ` [PATCH 19/62] watchdog: gpio_wdt: " Guenter Roeck 2017-01-10 23:34 ` [PATCH 20/62] watchdog: iTCO_wdt: Replace shutdown function with call to watchdog_stop_on_reboot Guenter Roeck 2017-01-11 23:36 ` Andy Shevchenko 2017-01-10 23:34 ` [PATCH 21/62] watchdog: imgpdc_wdt: Convert to use device managed functions and other improvements Guenter Roeck 2017-01-10 23:34 ` [PATCH 22/62] watchdog: imx2_wdt: Convert to use device managed functions Guenter Roeck 2017-01-10 23:34 ` [PATCH 23/62] watchdog: intel-mid_wdt: " Guenter Roeck 2017-01-11 23:36 ` Andy Shevchenko 2017-01-10 23:34 ` [PATCH 24/62] watchdog: jz4740_wdt: " Guenter Roeck 2017-01-10 23:34 ` [PATCH 25/62] watchdog: kempld_wdt: Convert to use device managed functions and other improvements Guenter Roeck 2017-01-10 23:34 ` [PATCH 26/62] watchdog: loongson1_wdt: Convert to use device managed functions Guenter Roeck 2017-01-10 23:34 ` [PATCH 27/62] watchdog: lpc18xx_wdt: Convert to use device managed functions and other improvements Guenter Roeck 2017-01-10 23:34 ` Guenter Roeck 2017-01-10 23:34 ` [PATCH 28/62] watchdog: max63xx_wdt: Convert to use device managed functions Guenter Roeck 2017-01-10 23:34 ` [PATCH 29/62] watchdog: max77620_wdt: " Guenter Roeck 2017-01-10 23:34 ` [PATCH 30/62] watchdog: mena21_wdt: Convert to use device managed functions and other improvements Guenter Roeck 2017-01-13 8:08 ` Johannes Thumshirn 2017-01-11 0:44 ` [PATCH 31/62] watchdog: menf21bmc_wdt: Convert to use device managed functions Guenter Roeck 2017-01-11 0:44 ` [PATCH 32/62] watchdog: meson_gxbb_wdt: Convert to use device managed functions and other improvements Guenter Roeck 2017-01-11 0:44 ` Guenter Roeck 2017-01-11 0:44 ` Guenter Roeck 2017-01-11 8:42 ` Neil Armstrong 2017-01-11 8:42 ` Neil Armstrong 2017-01-11 8:42 ` Neil Armstrong 2017-01-11 18:44 ` Kevin Hilman 2017-01-11 18:44 ` Kevin Hilman 2017-01-11 18:44 ` Kevin Hilman 2017-01-11 0:44 ` [PATCH 33/62] watchdog: meson_wdt: " Guenter Roeck 2017-01-11 0:44 ` Guenter Roeck 2017-01-11 0:44 ` Guenter Roeck 2017-01-11 18:45 ` Kevin Hilman 2017-01-11 18:45 ` Kevin Hilman 2017-01-11 18:45 ` Kevin Hilman 2017-01-11 0:44 ` [PATCH 34/62] watchdog: moxart_wdt: Convert to use device managed functions Guenter Roeck 2017-01-11 0:44 ` [PATCH 35/62] watchdog: mpc8xxx_wdt: " Guenter Roeck 2017-01-11 0:44 ` [PATCH 36/62] watchdog: mt7621_wdt: Convert to use device managed functions and other improvements Guenter Roeck 2017-01-11 0:44 ` [PATCH 37/62] watchdog: mtk_wdt: " Guenter Roeck 2017-01-11 0:44 ` Guenter Roeck 2017-01-11 0:44 ` [PATCH 38/62] watchdog: nic7018_wdt: Convert to use device managed functions Guenter Roeck 2017-01-11 0:44 ` [PATCH 39/62] watchdog: of_xilinx_wdt: " Guenter Roeck 2017-01-11 0:44 ` Guenter Roeck 2017-01-11 0:44 ` [PATCH 40/62] watchdog: omap_wdt: " Guenter Roeck 2017-01-11 0:44 ` [PATCH 41/62] watchdog: orion_wdt: Convert to use device managed functions and other improvements Guenter Roeck 2017-01-11 0:44 ` [PATCH 42/62] watchdog: pic32-dmt: Convert to use device managed functions Guenter Roeck 2017-01-11 0:44 ` [PATCH 43/62] watchdog: pic32-wdt: " Guenter Roeck 2017-01-11 0:44 ` [PATCH 44/62] watchdog: pnx4008_wdt: " Guenter Roeck 2017-01-11 0:44 ` Guenter Roeck 2017-01-12 0:13 ` Vladimir Zapolskiy 2017-01-12 0:13 ` Vladimir Zapolskiy 2017-01-11 0:44 ` [PATCH 45/62] watchdog: qcom-wdt: " Guenter Roeck 2017-01-11 0:44 ` [PATCH 46/62] watchdog: renesas_wdt: " Guenter Roeck 2017-01-11 0:44 ` [PATCH 47/62] watchdog: retu_wdt: Convert to use device managed functions and other improvements Guenter Roeck 2017-01-11 0:44 ` [PATCH 48/62] watchdog: rt2880_wdt: " Guenter Roeck 2017-01-11 0:44 ` [PATCH 49/62] watchdog: sama5d4_wdt: Convert to use device managed functions Guenter Roeck 2017-01-11 0:44 ` [PATCH 50/62] watchdog: sbsa_gwdt: Convert to use device managed functions and other improvements Guenter Roeck 2017-01-11 0:45 ` [PATCH 51/62] watchdog: shwdt: " Guenter Roeck 2017-01-11 2:09 ` [PATCH 52/62] watchdog: sirfsoc_wdt: " Guenter Roeck 2017-01-11 2:09 ` Guenter Roeck 2017-01-11 2:09 ` [PATCH 53/62] watchdog: st_lpc_wdt: Convert to use device managed functions Guenter Roeck 2017-01-11 2:09 ` Guenter Roeck 2017-01-11 2:09 ` [PATCH 54/62] watchdog: stmp3xxx_rtc_wdt: " Guenter Roeck 2017-01-11 2:09 ` [PATCH 55/62] watchdog: sunxi_wdt: Convert to use device managed functions and other improvements Guenter Roeck 2017-01-11 2:09 ` Guenter Roeck 2017-01-11 12:15 ` Maxime Ripard 2017-01-11 12:15 ` Maxime Ripard 2017-01-11 2:09 ` [PATCH 56/62] watchdog: tangox_wdt: Convert to use device managed functions Guenter Roeck 2017-01-11 2:09 ` Guenter Roeck 2017-01-11 9:07 ` Marc Gonzalez 2017-01-11 9:07 ` Marc Gonzalez 2017-01-11 10:52 ` Guenter Roeck 2017-01-11 10:52 ` Guenter Roeck 2017-01-11 12:31 ` Marc Gonzalez 2017-01-11 12:31 ` Marc Gonzalez 2017-01-11 14:25 ` Guenter Roeck 2017-01-11 14:25 ` Guenter Roeck 2017-01-11 14:43 ` Måns Rullgård 2017-01-11 14:43 ` Måns Rullgård 2017-01-11 15:28 ` Marc Gonzalez 2017-01-11 15:28 ` Marc Gonzalez 2017-01-11 17:51 ` Guenter Roeck 2017-01-11 17:51 ` Guenter Roeck 2017-01-12 9:44 ` Marc Gonzalez 2017-01-12 9:44 ` Marc Gonzalez 2017-01-12 9:57 ` Uwe Kleine-König 2017-01-12 9:57 ` Uwe Kleine-König 2017-01-12 11:24 ` Måns Rullgård [this message] 2017-01-12 11:24 ` Måns Rullgård 2017-01-12 12:15 ` Marc Gonzalez 2017-01-12 12:15 ` Marc Gonzalez 2017-01-11 14:39 ` Uwe Kleine-König 2017-01-11 14:39 ` Uwe Kleine-König 2017-01-11 14:50 ` Vladimir Zapolskiy 2017-01-11 14:50 ` Vladimir Zapolskiy 2017-01-11 17:28 ` Guenter Roeck 2017-01-11 17:28 ` Guenter Roeck 2017-01-13 5:17 ` Guenter Roeck 2017-01-13 5:17 ` Guenter Roeck 2017-01-12 0:12 ` Andy Shevchenko 2017-01-12 0:12 ` Andy Shevchenko 2017-01-12 1:29 ` Guenter Roeck 2017-01-12 1:29 ` Guenter Roeck 2017-01-11 2:09 ` [PATCH 57/62] watchdog: tegra_wdt: " Guenter Roeck [not found] ` <1484100561-17638-6-git-send-email-linux-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org> 2017-01-19 11:04 ` Thierry Reding 2017-01-19 11:04 ` Thierry Reding 2017-01-11 2:09 ` [PATCH 58/62] watchdog: ts4800_wdt: " Guenter Roeck 2017-01-11 2:09 ` [PATCH 59/62] watchdog: twl4030_wdt: " Guenter Roeck 2017-01-11 2:09 ` [PATCH 60/62] watchdog: txx9wdt: Convert to use device managed functions and other improvements Guenter Roeck 2017-01-11 2:09 ` [PATCH 61/62] watchdog: ux500_wdt: Convert to use device managed functions Guenter Roeck 2017-01-11 2:09 ` [PATCH 62/62] watchdog: wm831x_wdt: " Guenter Roeck 2017-01-12 10:04 ` Charles Keepax
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