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Re: [E-devel] elm_label problem with specific text
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From: Brian W. <bri...@gm...> - 2009-11-14 05:21:55
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On Sat, Nov 14, 2009 at 1:44 AM, Gustavo Sverzut Barbieri
<bar...@pr...> wrote:
> On Fri, Nov 13, 2009 at 3:13 PM, Brian Wang <bri...@gm...> wrote:
>> On Fri, Nov 13, 2009 at 8:12 PM, Gustavo Sverzut Barbieri
>> <bar...@pr...> wrote:
>>> On Fri, Nov 13, 2009 at 4:49 AM, Brian Wang <bri...@gm...> wrote:
>>>> [snip]
>>>>> OK. With the help of gdbserver/gdb, I am able to find where it's looping.
>>>>> However, I don't know what causes it. Here it goes:
>>>>> [svn r43601]
>>>>> evas/src/lib/canvas/evas_object_textblock.c:3152
>>>>
>>>> The line number is off... I've put some of my stuff in the front of
>>>> the source code... My bad.
>>>>
>>>>> evas_object_textblock_text_markup_get() calls
>>>>> escape = _escaped_char_match(p, &adv);
>>>>> _escaped_char_match() returns "" and 'adv' is set to 0
>>>>> thus the looping.
>>>>>
>>>>> Here is the gdb backtrace:
>>>>> --------------------------------------
>>>>> (gdb) bt
>>>>> #0 _escaped_char_match (s=0x780a1 "追 ", adv=0xbec8c490)
>>>>> at evas_object_textblock.c:2732
>>>>> #1 0x4008338c in evas_object_textblock_text_markup_get (obj=0x75380)
>>>>> at evas_object_textblock.c:3152
>>>>> #2 0x40826be0 in _edje_part_recalc_single (ed=0x0, ep=0x0, desc=0x75ae0,
>>>>> chosen_desc=0x40300000, rel1_to_x=0x0, rel1_to_y=0x40884c2c,
>>>>> rel2_to_x=0x3, rel2_to_y=0x751c0, confine_to=0x0, params=0x749ac, flags=3)
>>>>> at edje_calc.c:651
>>>>> #3 0x408271c8 in _edje_part_recalc (ed=0x10, ep=0x748bc, flags=1)
>>>>> at edje_calc.c:1721
>>>>> #4 0x40828e10 in _edje_recalc_do (ed=0x780a1) at edje_calc.c:224
>>>>> #5 0x408473b4 in edje_object_size_min_restricted_calc (
>>>>> obj=<value optimized out>, minw=0x0, minh=0x4025e27c, restrictedw=0,
>>>>> restrictedh=-1) at edje_util.c:2362
>>>>> #6 0x40847618 in edje_object_size_min_calc (obj=0x780a1, minw=0xbec8c490,
>>>>> minh=0x40144860) at edje_util.c:2311
>>>>> #7 0x40210a6c in _sizing_eval (obj=0x5d060) at elm_label.c:55
>>>>> #8 0x40210e10 in elm_label_label_set (obj=0x5d060, label=0x8c88 " 追 ")
>>>>> at elm_label.c:121
>>>>> #9 0x00008b1c in elm_main (argc=1, argv=0xbec8cd04) at elm-label-bug-test.c:36
>>>>> #10 0x00008bac in main (argc=1, argv=0xbec8cd04) at elm-label-bug-test.c:64
>>>>> --------------------------------------
>>>>>
>>>>> I don't know what's special about the string that makes it end up the condition.
>>>>> Checking if (strlen(escape)==0 && adv==0) seems to terminate the loop.
>>>>> But I totally have no clue what's going on here... Fixing it without
>>>>> knowing what's causing the condition is wrong.
>>>>>
>>>>> The string "追 " in UTF-8 is of value: 0xe8 0xbf 0xbd 0x20
>>>>>
>>>>> Is the info above enough to track down the problem?
>>>>
>>>> I've tracked it down a bit.
>>>> On x86, via gdb,
>>>> ------------------------
>>>> (gdb) p escape_strings[sizeof(escape_strings)]
>>>> $4 = 102 'f'
>>>> ------------------------
>>>>
>>>> On my arm, via gdb,
>>>> ------------------------
>>>> (gdb) p escape_strings[sizeof(escape_strings)]
>>>> $12 = 0 '\0'
>>>> ------------------------
>>>
>>> As you said below, it is invalid read.
>>>
>>>
>>>> At the very last check of
>>>> while ((*mc) && (*sc)),
>>>> map_itr is equal to map_end and the difference is the on x86 *mc is
>>>> non-zero and on my arm, *mc is zero.
>>>> Therefore, on arm, the while loop is skipped all together and 'match'
>>>> is still 1. And hence the looping...
>>>>
>>>> sizeof(escape_strings) on both platforms are the same: 1551.
>>>> I would say that it is invalid read for both cases. The x86 case gets
>>>> lucky and got away with it.
>>>> I'm surprised that valgrind did not catch this. Or maybe I'm wrong...
>>>> char a[] = "s";
>>>> sizeof(a) == 2
>>>> accessing a[2] is out of bounds
>>>
>>> this is correct. As why it does not warn, maybe there is another valid
>>> string allocated right after, thus you end reading something valid and
>>> valgrind will not warn you.
>>
>> I guess so too. I thought valgrind is pretty good at catching
>> out-of-bounds accesses..
>
> well, there are some flags to make GCC produce code with garbage
> before and after arrays, I guess it's fortify source or something like
> that. mudflap should help as well.
>
>
>>>> We may check if (map_itr < map_end) after the first
>>>> _advance_after_end_of_string() inside _escaped_char_match()
>>>> or we may decrease map_end by 1 since every escape character is
>>>> already terminated by a null character.
>>>> Thus, my proposed patch (sorry for the bad part at the front, which is
>>>> only for my own usage):
>>>> ------------------------------------------------
>>>> Index: src/lib/canvas/evas_object_textblock.c
>>>> ===================================================================
>>>> --- src/lib/canvas/evas_object_textblock.c (revision 43601)
>>>> +++ src/lib/canvas/evas_object_textblock.c (working copy)
>>>> @@ -1608,6 +1608,18 @@
>>>> _layout_word_start(char *str, int start)
>>>> {
>>>> int p, tp, chr = 0;
>>>> +
>>>> +#if 1
>>>> + //
>>>> + // coolbrian: break if the word is not within the ASCII range
>>>> + // @note This is good for breaking up Chinese words, which are
>>>> made of Chinese characters.
>>>> + // Chinese characters do not look strange if they are not
>>>> grouped to form a 'phrase'.
>>>> + // Also, Chinese 'phrases' are of too many patterns and
>>>> probably need a dictionary to look up.
>>>> + // That would be too much.
>>>> + //
>>>> + if (((unsigned char)str[start]) >= 0x80)
>>>> + return start;
>>>> +#endif
>>>>
>>>> p = start;
>>>> chr = evas_common_font_utf8_get_next((unsigned char *)(str), &p);
>>>> @@ -2709,7 +2721,7 @@
>>>> const char *map_itr, *map_end, *mc, *sc;
>>>>
>>>> map_itr = escape_strings;
>>>> - map_end = map_itr + sizeof(escape_strings);
>>>> + map_end = map_itr + sizeof(escape_strings) - 1;
>>>>
>>>> while (map_itr < map_end)
>>>
>>> It's weird:
>>>
>>> map_end = map_itr + sizeof(escape_strings)
>>>
>>> is fine, as we compare for less than, so this address would never be
>>> used. The last run should be on escape_strings:
>>> "⊥\0" "\xe2\x8a\xa5\0"
>>>
>>> Thus:
>>>
>>> while (map_itr < map_end)
>>>
>>> --> yes, we're at map_itr = ⊥\0
>>>
>>>
>>> {
>>> const char *escape;
>>> int match;
>>>
>>> escape = map_itr;
>>>
>>> --> escape = ⊥\0
>>>
>>>
>>> _advance_after_end_of_string(&map_itr);
>>> mc = map_itr;
>>>
>>> --> map_itr = \xe2\x8a\xa5\0
>>>
>>>
>>> sc = s;
>>> match = 1;
>>> while ((*mc) && (*sc))
>>> {
>>>
>>> --> enters
>>>
>>>
>>> if ((unsigned char)*sc < (unsigned char)*mc) return NULL;
>>>
>>> --> I have no clue why this
>>
>> I don't either...
>>
>>>
>>>
>>> if (*sc != *mc) match = 0;
>>>
>>> --> fails, thus match = 0
>>>
>>>
>>> mc++;
>>> sc++;
>>> }
>>> if (match)
>>>
>>> --> skipped, as match = 0
>>>
>>> {
>>> *adv = mc - map_itr;
>>> return escape;
>>> }
>>> _advance_after_end_of_string(&map_itr);
>>>
>>> --> map_itr was \xe2\x8a\xa5\0, thus it's now one byte after, thus
>>> map_itr == escape_strings + sizeof(escape_strings) and thus the next
>>> while (map_itr < map_end) will fail.
>>
>> No. map_itr == escape_strings + sizeof(escape_strings) -1
>> Thus the next while (map_itr < map_end) will pass.
>
> So that's the bug. If map_itr was \xe2\x8a\xa5\0 and
> _advance_after_end_of_string(&map_itr); looks for the first \0 (the
> last char) then increments one, we clearly should be correct! :-(
>
>
>> If we simplify the string a bit:
>> char escape_strings[] = "\xe2\x8a\0"; // sizeof it == 4
>> say escape_strings is at address 0x0
>> map_itr = 0;
>> map_end = 0 + 4 = 4;
>> _advance_after_end_of_string(&map_itr);
>> map_itr=3;
>
> what?! how advance after of string is returning 3???
> it should read 3 times, stop since it found 0, then increment one...
> please debug that one :-)
static void _advance_after_end_of_string(const char **p_buf)
{
while (**p_buf != 0) (*p_buf)++;
(*p_buf)++;
}
After the while loop, *p_buf=2 (read 3 times but the 3rd time does not
increment it). The second line would make it 3.
Please have a look at the attached file.
>
>
> --
> Gustavo Sverzut Barbieri
> http://profusion.mobi embedded systems
> --------------------------------------
> MSN: bar...@gm...
> Skype: gsbarbieri
> Mobile: +55 (19) 9225-2202
>
--
brian
------------------
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