linux-kernel - Re: [PATCH 2/5] [v2] acpi: disable -Wstringop-truncation

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Date: Wed, 10 Apr 2024 21:10:01 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Arnd Bergmann <arnd@...nel.org>
Cc: linux-kbuild@...r.kernel.org, Arnd Bergmann <arnd@...db.de>, 
	Richard Russon <ldm@...tcap.org>, Jens Axboe <axboe@...nel.dk>, 
	Robert Moore <robert.moore@...el.com>, "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, 
	Len Brown <lenb@...nel.org>, Steven Rostedt <rostedt@...dmis.org>, 
	Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Masahiro Yamada <masahiroy@...nel.org>, 
	Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>, 
	Lin Ming <ming.m.lin@...el.com>, Alexey Starikovskiy <astarikovskiy@...e.de>, 
	linux-ntfs-dev@...ts.sourceforge.net, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-acpi@...r.kernel.org, acpica-devel@...ts.linux.dev, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] [v2] acpi: disable -Wstringop-truncation

Hi,

On Tue, Apr 09, 2024 at 04:00:55PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> gcc -Wstringop-truncation warns about copying a string that results in a
> missing nul termination:
> 
> drivers/acpi/acpica/tbfind.c: In function 'acpi_tb_find_table':
> drivers/acpi/acpica/tbfind.c:60:9: error: 'strncpy' specified bound 6 equals destination size [-Werror=stringop-truncation]
>    60 |         strncpy(header.oem_id, oem_id, ACPI_OEM_ID_SIZE);
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/acpi/acpica/tbfind.c:61:9: error: 'strncpy' specified bound 8 equals destination size [-Werror=stringop-truncation]
>    61 |         strncpy(header.oem_table_id, oem_table_id, ACPI_OEM_TABLE_ID_SIZE);
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> The code works as intended, and the warning could be addressed by using
> a memcpy(), but turning the warning off for this file works equally well
> and may be easir to merge.

Dang, I would've really liked to see these strncpy()'s dealt with [1]!

The warning is there because that specific usage of strncpy is plain
wrong. strncpy() is a string api and this usage looks like it has
arguments and results not resembling C-strings.

Not sure if turning off correct warnings is the right call.

Link: https://github.com/KSPP/linux/issues/90 [1]

> 
> Fixes: 47c08729bf1c ("ACPICA: Fix for LoadTable operator, input strings")
> Link: https://lore.kernel.org/lkml/CAJZ5v0hoUfv54KW7y4223Mn9E7D4xvR7whRFNLTBqCZMUxT50Q@mail.gmail.com/#t
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/acpi/acpica/Makefile | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/acpi/acpica/Makefile b/drivers/acpi/acpica/Makefile
> index 30f3fc13c29d..8d18af396de9 100644
> --- a/drivers/acpi/acpica/Makefile
> +++ b/drivers/acpi/acpica/Makefile
> @@ -5,6 +5,7 @@
>  
>  ccflags-y			:= -D_LINUX -DBUILDING_ACPICA
>  ccflags-$(CONFIG_ACPI_DEBUG)	+= -DACPI_DEBUG_OUTPUT
> +CFLAGS_tbfind.o 		+= $(call cc-disable-warning, stringop-truncation)
>  
>  # use acpi.o to put all files here into acpi.o modparam namespace
>  obj-y	+= acpi.o
> -- 
> 2.39.2
> 

Thanks
Justin