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bug#9983: valgrind warning in draw_glyphs


From: Dan Nicolaescu
Subject: bug#9983: valgrind warning in draw_glyphs
Date: Mon, 07 Nov 2011 06:52:03 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.3 (gnu/linux)

Eli Zaretskii <address@hidden> writes:

>> From: Dan Nicolaescu <address@hidden>
>> Date: Sun, 06 Nov 2011 23:36:42 -0500
>> 
>> The warning is for this:
>>         if (check_mouse_face
>>               && mouse_beg_col < start && mouse_end_col > i)
>> 
>> it looks like mouse_beg_col and mouse_end_col could be left uninitialized a 
>> few lines above.
>
> I don't see how.  These variables are initialized in this block:
>
>         if (row >= mouse_beg_row && row <= mouse_end_row)
>           {
>             check_mouse_face = 1;
>             mouse_beg_col = (row == mouse_beg_row)
>               ? hlinfo->mouse_face_beg_col : 0;
>             mouse_end_col = (row == mouse_end_row)
>               ? hlinfo->mouse_face_end_col
>               : row->used[TEXT_AREA];
>           }
>
> check_mouse_face starts as zero, and is only set to 1 in this block.
> So any test that is conditioned on check_mouse_face being non-zero is
> okay with looking at mouse_beg_col and mouse_end_col.
>
> The other variables in the line being flagged, `start' and `i', are
> also okay: `start' is one of the call arguments and `i' is computed
> right before the line being flagged.
>
> Did I miss something?

Hmm, you might be right.  Telling valgrind to attach gdb at that point:

(gdb) info local
overlap_hl = <optimized out>
hlinfo = <optimized out>
mouse_beg_col = 0x0
check_mouse_face = 0x0
dummy_x = 0x0
h = <optimized out>
t = <optimized out>
mouse_end_col = 0x50b3a22
head = 0x7feffe3a0
tail = 0x7feffe3a0
s = <optimized out>
clip_head = 0x0
clip_tail = 0x0
i = <optimized out>
j = <optimized out>
x_reached = 0x184
last_x = 0x2ec
area_left = 0x1c
f = 0x5157bf0

Maybe a compiler problem, evaluating the && in the wrong order?





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