[Geany-devel] RFC: uninitialized variable in theoretical execution path.

[Daniel Marjamäki]

Hi!

I wonder what you think about fixing "uninitialized variable" issues
for theoretical execution paths.

What I mean with "theoretical" is that it is not assumed that
parameters and global variables are restricted to the "possible"
values - they could also have "impossible values".

An example:

An uninitialized variable "y" can theoretically be used in
src/printing.c at line 753.

Here is the code in shortened format:

514     gdouble x, y;

561     while (count < dinfo->lines_per_page)
       {
686                     cairo_get_current_point(cr, &x, &y);
       }

742     if (printing_prefs.print_line_numbers)
       {
752             cairo_line_to(cr, (dinfo->max_line_number_margin *
dinfo->font_width) + 1,
                       y + dinfo->line_height); /* y is last added
line, we reuse it */
       }

The variable "y" is initialized in the loop. If the loop is skipped
the variable will not be initialized. Therefore if
dinfo->lines_per_page is 0 and printing_prefs.print_line_numbers is
true then there will be a "uninitialized variable" issue.

I guess there is an assumption that dinfo->lines_per_page will always
be greater than 0. Perhaps that assumption is ok.

Best regards,
Daniel


PS.

I wrote a simple Cppcheck plugin that searches for "uninitialized
variable" in "theoretical execution paths". It will assume that all
conditions can always be both true/false.

I assume that most of the reports are false positives. But if you are
interested.. here is what it says for geany/src:

[src/dialogs.c:257]: (information) Suspecting that uninitialized
variable is used: iter_parent
[src/dialogs.c:684]: (information) Suspecting that uninitialized
variable is used: resp
[src/dialogs.c:740]: (information) Suspecting that uninitialized
variable is used: title
[src/dialogs.c:774]: (information) Suspecting that uninitialized
variable is used: args
[src/dialogs.c:1663]: (information) Suspecting that uninitialized
variable is used: args
[src/dialogs.c:1686]: (information) Suspecting that uninitialized
variable is used: args
[src/dialogs.c:1713]: (information) Suspecting that uninitialized
variable is used: args
[src/editor.c:2852]: (information) Suspecting that uninitialized
variable is used: style_comment
[src/editor.c:4890]: (information) Suspecting that uninitialized
variable is used: mode
[src/encodings.c:643]: (information) Suspecting that uninitialized
variable is used: charset
[src/filetypes.c:854]: (information) Suspecting that uninitialized
variable is used: args
[src/filetypes.c:1395]: (information) Suspecting that uninitialized
variable is used: result
[src/keybindings.c:1543]: (information) Suspecting that uninitialized
variable is used: item
[src/log.c:68]: (information) Suspecting that uninitialized variable
is used: args
[src/msgwindow.c:269]: (information) Suspecting that uninitialized
variable is used: args
[src/msgwindow.c:341]: (information) Suspecting that uninitialized
variable is used: args
[src/msgwindow.c:399]: (information) Suspecting that uninitialized
variable is used: args
[src/printing.c:753]: (information) Suspecting that uninitialized
variable is used: y
[src/socket.c:685]: (information) Suspecting that uninitialized
variable is used: newline
[src/stash.c:767]: (information) Suspecting that uninitialized
variable is used: args
[src/stash.c:1057]: (information) Suspecting that uninitialized
variable is used: setting
[src/symbols.c:205]: (information) Suspecting that uninitialized
variable is used: tag_type
[src/symbols.c:636]: (information) Suspecting that uninitialized
variable is used: args
[src/symbols.c:1917]: (information) Suspecting that uninitialized
variable is used: fn_style
[src/templates.c:577]: (information) Suspecting that uninitialized
variable is used: args
[src/tools.c:127]: (information) Suspecting that uninitialized
variable is used: stock_id
[src/ui_utils.c:148]: (information) Suspecting that uninitialized
variable is used: args
[src/ui_utils.c:885]: (information) Suspecting that uninitialized
variable is used: widget_name
[src/ui_utils.c:1842]: (information) Suspecting that uninitialized
variable is used: args
[src/ui_utils.c:2365]: (information) Suspecting that uninitialized
variable is used: a
[src/utils.c:1365]: (information) Suspecting that uninitialized
variable is used: a
[src/utils.c:2090]: (information) Suspecting that uninitialized
variable is used: args
[src/win32.c:713]: (information) Suspecting that uninitialized
variable is used: t
[src/win32.c:705]: (information) Suspecting that uninitialized
variable is used: title

There could be a real issue in one of those reports but I don't know
how likely that is.

I am in the process right now to analyse the results. If I see genuine
problems I'll report them.