linux-kernel - Re: [-mm PATCH] kallsyms should prefer non weak symbols

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Date:	Wed, 5 Dec 2007 00:01:18 -0500
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Paulo Marques <pmarques@...popie.com>,
	linux-kernel@...r.kernel.org, Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [-mm PATCH] kallsyms should prefer non weak symbols

* Andrew Morton (akpm@...ux-foundation.org) wrote:
> On Tue, 04 Dec 2007 20:35:32 +0000 Paulo Marques <pmarques@...popie.com> wrote:
> 
> > When resolving symbol names from addresses with aliased symbol names, 
> > kallsyms_lookup always returns the first symbol, even if it is a weak 
> > symbol.
> > 
> > This patch changes this by sorting the symbols with the weak symbols 
> > last before feeding them to the kernel. This way the kernel runtime 
> > isn't changed at all, only the kallsyms build system is changed.
> > 
> > Another side effect is that the symbols get sorted by address, too. So, 
> > even if future binutils version have some bug in "nm" that makes it fail 
> > to correctly sort symbols by address, the kernel won't be affected by this.
> 
> Incremental patch:
> 
> 
> 
> 
> From: Andrew Morton <akpm@...ux-foundation.org>
> 
> Fix checkpatch warnings:
> 
> ERROR: do not use C99 // comments
> #72: FILE: scripts/kallsyms.c:516:
> +	// sort by address first
> 
> ERROR: do not use C99 // comments
> #78: FILE: scripts/kallsyms.c:522:
> +	// sort by "weakness" type
> 
> ERROR: do not use C99 // comments
> #84: FILE: scripts/kallsyms.c:528:
> +	// sort by initial order, so that other symbols are left undisturbed
> 
> total: 3 errors, 0 warnings, 61 lines checked
> 
> Your patch has style problems, please review.  If any of these errors
> are false positives report them to the maintainer, see
> CHECKPATCH in MAINTAINERS.
> 
> Please run checkpatch prior to sending patches
> 
> And a few coding-style things which checkpatch missed.
> 
> And fix up constificiation to remove typecasting.
> 
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> Cc: Paulo Marques <pmarques@...popie.com>
> Cc: Sam Ravnborg <sam@...nborg.org>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>

(if it's any useful at this point) The comments were the only problems I
found. I've tested it and it work fine for me in LTTng.

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>

> ---
> 
>  scripts/kallsyms.c |   19 +++++++++----------
>  1 file changed, 9 insertions(+), 10 deletions(-)
> 
> diff -puN scripts/kallsyms.c~kallsyms-should-prefer-non-weak-symbols-checkpatch-fixes scripts/kallsyms.c
> --- a/scripts/kallsyms.c~kallsyms-should-prefer-non-weak-symbols-checkpatch-fixes
> +++ a/scripts/kallsyms.c
> @@ -31,14 +31,13 @@
>  
>  #define KSYM_NAME_LEN		128
>  
> -
>  struct sym_entry {
>  	unsigned long long addr;
> -	unsigned int len, start_pos;
> +	unsigned int len;
> +	unsigned int start_pos;
>  	unsigned char *sym;
>  };
>  
> -
>  static struct sym_entry *table;
>  static unsigned int table_size, table_cnt;
>  static unsigned long long _text, _stext, _etext, _sinittext, _einittext;
> @@ -504,28 +503,28 @@ static void optimize_token_table(void)
>  	optimize_result();
>  }
>  
> -
>  static int compare_symbols(const void *a, const void *b)
>  {
> -	struct sym_entry *sa, *sb;
> +	const struct sym_entry *sa;
> +	const struct sym_entry *sb;
>  	int wa, wb;
>  
> -	sa = (struct sym_entry *) a;
> -	sb = (struct sym_entry *) b;
> +	sa = a;
> +	sb = b;
>  
> -	// sort by address first
> +	/* sort by address first */
>  	if (sa->addr > sb->addr)
>  		return 1;
>  	if (sa->addr < sb->addr)
>  		return -1;
>  
> -	// sort by "weakness" type
> +	/* 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
> +	/* sort by initial order, so that other symbols are left undisturbed */
>  	return sa->start_pos - sb->start_pos;
>  }
>  
> _
> 

-- 
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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