Re: [PATCH] perf symbols/KCORE: Rebuild rbtree when adjusting symbols for kcore

[Adrian Hunter <adrian.hunter@intel.com>]

On 11/11/15 22:44, Arnaldo Carvalho de Melo wrote:
> Em Wed, Nov 11, 2015 at 03:02:35PM +0800, Wangnan (F) escreveu:
>>
>>
>> On 2015/11/6 21:59, Adrian Hunter wrote:
>>> On 06/11/15 15:19, Arnaldo Carvalho de Melo wrote:
>>>> Em Fri, Nov 06, 2015 at 09:46:12AM +0000, Wang Nan escreveu:
>>>>> In dso__split_kallsyms_for_kcore(), current code adjusts symbol's
>>>>> address but only reinsert it into rbtree if the symbol belongs to
>>>>> another map. However, the expression for adjusting symbol (pos->start -=
>>>>> curr_map->start - curr_map->pgoff) can change the relative order between
>>>>> two symbols (even if the affected symbols are in different maps, in
>>>>> kcore case they are possible to share one same dso), which damages the
>>>>> rbtree.
>>>> Right, some code does change the symbol values it gets from whatever
>>>> symtab (kallsyms, ELF, JIT maps, etc) when it should instead use the per
>>>> map data structure (struct map) and its ->{map,unmap}_ip, ->pgoff,
>>>> ->reloc, members for that :-\
>>>>
>>>> I.e. 'struct dso' should be just what comes from the symtab, while
>>>> 'struct map' should be about where that DSO is in memory.
>>>>
>>>> With that in mind, do you still think your fix is the correct one?
>>>>
>>>> Adrian?
>>> The problem is when the order in memory (in kallsyms) is different
>>> to the order on the dso (kcore).
>>>
>>> I think to make it more general it needs to insert to a new tree.
>>> e.g.
>>>
>>
>> I have tested this patch and it works for me.
>>
>> Thank you.
> 
> Adrian, I took your explanation as the commit log, adding your S-o-B, so
> far not provided, is that ok with you, can I have your S-o-B?

Yes.  Thank you!

> 
>>From 500fe7dbd2c6cebc3638196352439490e1e3a8a4 Mon Sep 17 00:00:00 2001
> From: Adrian Hunter <adrian.hunter@intel.com>
> Date: Fri, 6 Nov 2015 15:59:29 +0200
> Subject: [PATCH 1/1] perf symbols: Rebuild rbtree when adjusting symbols for
>  kcore
> 
> Normally symbols are read from the DSO and adjusted, if need be, so that
> the symbol start matches the file offset in the DSO file (we want the
> file offset because that is what we know from MMAP events). That is done
> by dso__load_sym() which inserts the symbols *after* adjusting them.
> 
> In the case of kcore, the symbols have been read from kallsyms and the
> symbol start is the memory address. The symbols have to be adjusted to
> match the kcore file offsets. dso__split_kallsyms_for_kcore() does that,
> but now the adjustment is being done *after* the symbols have been
> inserted. It appears dso__split_kallsyms_for_kcore() was assuming that
> changing the symbol start would not change the order in the rbtree -
> which is, of course, not guaranteed.
> 
> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> Tested-by: Wang Nan <wangnan0@huawei.com>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Zefan Li <lizefan@huawei.com>
> Cc: pi3orama@163.com
> Link: http://lkml.kernel.org/r/563CB241.2090701@intel.com
> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> ---
>  tools/perf/util/symbol.c | 30 ++++++++++++++----------------
>  1 file changed, 14 insertions(+), 16 deletions(-)
> 
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index b4cc7662677e..09343a880c0b 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -654,19 +654,24 @@ static int dso__split_kallsyms_for_kcore(struct dso *dso, struct map *map,
>  	struct map_groups *kmaps = map__kmaps(map);
>  	struct map *curr_map;
>  	struct symbol *pos;
> -	int count = 0, moved = 0;
> +	int count = 0;
> +	struct rb_root old_root = dso->symbols[map->type];
>  	struct rb_root *root = &dso->symbols[map->type];
>  	struct rb_node *next = rb_first(root);
>  
>  	if (!kmaps)
>  		return -1;
>  
> +	*root = RB_ROOT;
> +
>  	while (next) {
>  		char *module;
>  
>  		pos = rb_entry(next, struct symbol, rb_node);
>  		next = rb_next(&pos->rb_node);
>  
> +		rb_erase_init(&pos->rb_node, &old_root);
> +
>  		module = strchr(pos->name, '\t');
>  		if (module)
>  			*module = '\0';
> @@ -674,28 +679,21 @@ static int dso__split_kallsyms_for_kcore(struct dso *dso, struct map *map,
>  		curr_map = map_groups__find(kmaps, map->type, pos->start);
>  
>  		if (!curr_map || (filter && filter(curr_map, pos))) {
> -			rb_erase_init(&pos->rb_node, root);
>  			symbol__delete(pos);
> -		} else {
> -			pos->start -= curr_map->start - curr_map->pgoff;
> -			if (pos->end)
> -				pos->end -= curr_map->start - curr_map->pgoff;
> -			if (curr_map->dso != map->dso) {
> -				rb_erase_init(&pos->rb_node, root);
> -				symbols__insert(
> -					&curr_map->dso->symbols[curr_map->type],
> -					pos);
> -				++moved;
> -			} else {
> -				++count;
> -			}
> +			continue;
>  		}
> +
> +		pos->start -= curr_map->start - curr_map->pgoff;
> +		if (pos->end)
> +			pos->end -= curr_map->start - curr_map->pgoff;
> +		symbols__insert(&curr_map->dso->symbols[curr_map->type], pos);
> +		++count;
>  	}
>  
>  	/* Symbols have been adjusted */
>  	dso->adjust_symbols = 1;
>  
> -	return count + moved;
> +	return count;
>  }
>  
>  /*
>