linux-kernel - Re: arm64: kernel/sys.c - silence initialization warnings.

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Message-ID: <20210315111433.GA22897@arm.com>
Date:   Mon, 15 Mar 2021 11:14:34 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Valdis Klētnieks <valdis.kletnieks@...edu>
Cc:     Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: arm64: kernel/sys.c - silence initialization warnings.

On Fri, Mar 12, 2021 at 04:55:46AM -0500, Valdis Klētnieks wrote:
> Building arch/arm64/kernel/sys.o with W=1 throws over 300 warnings:
> 
> /usr/src/linux-next/arch/arm64/kernel/sys.c:56:40: warning: initialized field overwritten [-Woverride-init]
>    56 | #define __SYSCALL(nr, sym)      [nr] = __arm64_##sym,
>       |                                        ^~~~~~~~
> /usr/src/linux-next/include/uapi/asm-generic/unistd.h:29:37: note: in expansion of macro '__SYSCALL'
>    29 | #define __SC_COMP(_nr, _sys, _comp) __SYSCALL(_nr, _sys)
>       |                                     ^~~~~~~~~
> /usr/src/linux-next/include/uapi/asm-generic/unistd.h:34:1: note: in expansion of macro '__SC_COMP'
>    34 | __SC_COMP(__NR_io_setup, sys_io_setup, compat_sys_io_setup)
>       | ^~~~~~~~~
> 
> We know that's pretty much the file's purpose in life, so tell the
> build system to not remind us.  This makes the 1 other warning a
> lot more noticeable. 
> 
> Signed-off-by: Valdis Kletnieks <valdis.kletnieks@...edu>
> 
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index ed65576ce710..916b21d2b35b 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -8,6 +8,7 @@ CFLAGS_armv8_deprecated.o := -I$(src)
>  CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)
>  CFLAGS_REMOVE_insn.o = $(CC_FLAGS_FTRACE)
>  CFLAGS_REMOVE_return_address.o = $(CC_FLAGS_FTRACE)
> +CFLAGS_sys.o += $(call cc-disable-warning, override-init)

We do similar initialisation in arch/arm64/kernel/sys32.c and
arch/arm64/kernel/traps.c for example. It's a pretty common pattern
throughout the kernel.

So we either treat W=1 output as diff against the vanilla kernel when
checking new patches or we remove override-init altogether from W=1.
Mark Rutland pointed me to an older thread:

https://lore.kernel.org/linux-arm-kernel/20190809083251.GA48423@lakrids.cambridge.arm.com/

-- 
Catalin