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From: Alexander Cherepanov <ch3root@openwall.com>
To: elfutils-devel@lists.fedorahosted.org
Subject: Re: [PATCH] libdwfl: Fix wrong type to make gcc -fsanitize=undefined
 happy.
Date: Thu, 23 Apr 2015 18:06:18 +0300
Message-ID: <55390A6A.4010509@openwall.com>
In-Reply-To: 20150421202612.E9A172C3AC8@topped-with-meat.com

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On 2015-04-21 23:26, Roland McGrath wrote:
> I think it's cleaner to do:
>
> [PATCH] libdwfl: Make dwfl_error.c C99-kosher.
>
> Signed-off-by: Roland McGrath <roland-/Z5OmTQCD9xF6kxbq+BtvQ(a)public.gma=
ne.org>
> ---
>   libdwfl/ChangeLog    |  7 +++++++
>   libdwfl/dwfl_error.c | 21 +++++++++++++++++----
>   2 files changed, 24 insertions(+), 4 deletions(-)
>
> diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
> index d4cd3f5..045adb0 100644
> --- a/libdwfl/ChangeLog
> +++ b/libdwfl/ChangeLog
> @@ -1,3 +1,10 @@
> +2015-04-21  Roland McGrath  <roland-/Z5OmTQCD9xF6kxbq+BtvQ(a)public.gman=
e.org>
> +
> +	* dwfl_error.c (struct msgtable): Break type definition out of
> +	the 'msgtable' initializer.
> +	(msgtable): Make it a union of struct msgtable and a char array.
> +	(msgstr): Use the full-table char array rather than the msg_0 entry.
> +
>   2015-04-02  Mark Wielaard  <mjw-H+wXaHxf7aLQT0dZR+AlfA(a)public.gmane.o=
rg>
>
>   	* segment.c (insert): Check correct number of lookup_elts.
> diff --git a/libdwfl/dwfl_error.c b/libdwfl/dwfl_error.c
> index d9ca9e7..f46b160 100644
> --- a/libdwfl/dwfl_error.c
> +++ b/libdwfl/dwfl_error.c
> @@ -1,5 +1,5 @@
>   /* Error handling in libdwfl.
> -   Copyright (C) 2005-2010 Red Hat, Inc.
> +   Copyright (C) 2005-2015 Red Hat, Inc.
>      This file is part of elfutils.
>
>      This file is free software; you can redistribute it and/or modify
> @@ -54,18 +54,31 @@ dwfl_errno (void)
>   INTDEF (dwfl_errno)
>
>
> -static const struct msgtable
> +struct msgtable
>   {
>   #define DWFL_ERROR(name, text) char msg_##name[sizeof text];
>     DWFL_ERRORS
>   #undef	DWFL_ERROR
> +};
> +
> +static const union
> +{
> +  struct msgtable table;
> +  char strings[
> +#define DWFL_ERROR(name, text)	sizeof text +
> +	       DWFL_ERRORS
> +#undef	DWFL_ERROR
> +	       + 0];

Extra plus in front of 0? Why not just use sizeof(struct msgtable)?

>   } msgtable =3D
>     {
> +    .table =3D
> +    {
>   #define DWFL_ERROR(name, text) text,
> -  DWFL_ERRORS
> +      DWFL_ERRORS
>   #undef	DWFL_ERROR
> +    }
>     };
> -#define msgstr (&msgtable.msg_NOERROR[0])
> +#define msgstr (msgtable.strings)

Something like can be done without unions:

#define msgstr (*(char (*)[sizeof msgtable])&msgtable)

AFACT it's well-defined C and permits to perform bound checking.

-- =

Alexander Cherepanov

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