Date: Tue, 13 Nov 2007 14:15:37 -0500
From: Mathieu Desnoyers <compudj@krystal.dyndns.org>
To: akpm@linux-foundation.org, linux-kernel@vger.kernel.org
Cc: Paulo Marques <pmarques@grupopie.com>,
       Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: [PATCH] Kallsyms Should Prefer Non Weak Symbols
Message-ID: <20071113191537.GB1125@Krystal>
References: <20071113191355.GA1125@Krystal>
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* Mathieu Desnoyers (mathieu.desnoyers@polymtl.ca) wrote:
> > [...]
> > kallsyms returns the first symbol encountered, even though it is weak,
> > when it should in fact return sys_ni_syscall.
> > Is it a concern for anyone else out there ? Would it make sense to fix
> > it ?
> 
> I don't know if it is a concern, but if we're going to fix it, we should
> probably do it in "scripts/kallsyms" by providing a list that is already
> sorted according to "address, weakness".
> 
> This way the run-time kernel keeps the current behavior, without any
> overhead. Something along the lines of the attached patch (just compile
> tested).
> 
> However, this is an area where we've had problems in the past with some
> architectures giving different results between passes, and then any change
> to the symbol order might make the problem worse and make the build process
> fail with a "Inconsistent kallsyms data" error message.
> 
> So, if someone wants to use this, it should go through -mm for a while,
> first.
> 
> It applies on top of 2.6.24-rc2-git3.
> 

Please use this reply with correct CC list for further discussion.

> From: Paulo Marques <pmarques@grupopie.com>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
> CC: Rusty Russell <rusty@rustcorp.com.au>
> ---
>  scripts/kallsyms.c |   36 ++++++++++++++++++++++++++++++++++--
>  1 file changed, 34 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6-lttng/scripts/kallsyms.c
> ===================================================================
> --- linux-2.6-lttng.orig/scripts/kallsyms.c	2007-10-31 21:38:36.000000000 -0400
> +++ linux-2.6-lttng/scripts/kallsyms.c	2007-10-31 22:29:28.000000000 -0400
> @@ -34,7 +34,7 @@
>  
>  struct sym_entry {
>  	unsigned long long addr;
> -	unsigned int len;
> +	unsigned int len, start_pos;
>  	unsigned char *sym;
>  };
>  
> @@ -202,8 +202,10 @@ static void read_map(FILE *in)
>  				exit (1);
>  			}
>  		}
> -		if (read_symbol(in, &table[table_cnt]) == 0)
> +		if (read_symbol(in, &table[table_cnt]) == 0) {
> +			table[table_cnt].start_pos = table_cnt;
>  			table_cnt++;
> +		}
>  	}
>  }
>  
> @@ -507,6 +509,35 @@ static void optimize_token_table(void)
>  }
>  
>  
> +static int compare_symbols(const void *a, const void *b)
> +{
> +	struct sym_entry *sa, *sb;
> +	int wa, wb;
> +
> +	sa = (struct sym_entry *) a;
> +	sb = (struct sym_entry *) b;
> +
> +	/* sort by address first */
> +	if (sa->addr > sb->addr)
> +		return 1;
> +	if (sa->addr < sb->addr)
> +		return -1;
> +
> +	/* sort by "weakness" type */
> +	wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W');
> +	wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W');
> +	if (wa != wb)
> +		return wa - wb;
> +
> +	/* sort by initial order, so that other symbols are left undisturbed */
> +	return sa->start_pos - sb->start_pos;
> +}
> +
> +static void sort_symbols(void)
> +{
> +	qsort(table, table_cnt, sizeof(struct sym_entry), compare_symbols);
> +}
> +
>  int main(int argc, char **argv)
>  {
>  	if (argc >= 2) {
> @@ -527,6 +558,7 @@ int main(int argc, char **argv)
>  		usage();
>  
>  	read_map(stdin);
> +	sort_symbols();
>  	optimize_token_table();
>  	write_src();
>  
> 
> -- 
> Mathieu Desnoyers
> Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
> OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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