Dominique wrote:
> In runtime/doc/todo.txt, I see this item:
>
> Conditional jump or move depends on uninitialised value(s)
> ==2819005== at 0x2E9134: jump_to_mouse (mouse.c:2015)
> ==2819005== by 0x2E69E6: do_mouse (mouse.c:702)
> ==2819005== by 0x2E95C2: nv_mouse (mouse.c:2166)
>
> If we add the valgrind option --track-origins=yes then we can
> see where the uninitialized memory comes from:
>
> ==10697== Conditional jump or move depends on uninitialised value(s)
> ==10697== at 0x2A2225: jump_to_mouse (mouse.c:2015)
> ==10697== by 0x2A0544: do_mouse (mouse.c:702)
> ==10697== by 0x2AA3A6: normal_cmd (normal.c:937)
> ==10697== by 0x225F0C: exec_normal (ex_docmd.c:0)
> ==10697== by 0x1FFF49: f_feedkeys (evalfunc.c:4352)
[...]
> ==10697== by 0x440B9A: main (main.c:432)
>
> ==10697== Uninitialised value was created by a heap allocation
> ==10697== at 0x40367BA: malloc (vg_replace_malloc.c:393)
> ==10697== by 0x1A5477: lalloc (alloc.c:246)
> ==10697== by 0x329CC9: screenalloc (screen.c:2711)
> ==10697== by 0x32AD3D: screenclear (screen.c:2981)
> ==10697== by 0x3775FB: set_shellsize (term.c:3436)
> ==10697== by 0x3767EA: set_termname (term.c:2063)
> ==10697== by 0x4406CC: main (main.c:368)
>
> So the uninitialized memory comes from screen.c:2711:
>
> 2711 new_ScreenCols = LALLOC_MULT(colnr_T, (Rows + 1) * Columns);
>
> This one-line patch fixes it:
>
> diff --git a/src/screen.c b/src/screen.c
> index 27f484837..17a6fd24e 100644
> --- a/src/screen.c
> +++ b/src/screen.c
> @@ -2708,7 +2708,7 @@ retry:
> if (enc_dbcs == DBCS_JPNU)
> new_ScreenLines2 = LALLOC_MULT(schar_T, (Rows + 1) * Columns);
> new_ScreenAttrs = LALLOC_MULT(sattr_T, (Rows + 1) * Columns);
> - new_ScreenCols = LALLOC_MULT(colnr_T, (Rows + 1) * Columns);
> + new_ScreenCols = LALLOC_CLEAR_MULT(colnr_T, (Rows + 1) * Columns);
> new_LineOffset = LALLOC_MULT(unsigned, Rows);
> new_LineWraps = LALLOC_MULT(char_u, Rows);
> new_TabPageIdxs = LALLOC_MULT(short, Columns);
>
> However, I am not sure that the fix is correct as
> the function screenalloc(...) has a doclear parameter,
> so maybe it's the caller that should have called
> screenalloc(TRUE)?
Thanks for looking into this. The warning would be for this line:
if (col_from_screen >= 0)
Which was set here:
// Only use ScreenCols[] after the window was redrawn. Mainly matters
// for tests, a user would not click before redrawing.
// Do not use when 'virtualedit' is active.
if (curwin->w_redr_type <= UPD_VALID_NO_UPDATE && !virtual_active())
col_from_screen = ScreenCols[off];
Apparently the condition doesn't always work. Clearing the whole block
of allocated memory is not cheap, but it won't happen often anyway.
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