Hi everyone,
I'm currently working on new warnings for gcc's -fanalyzer. I've
implemented a version of Wrestrict inside the analyzer, using its
region model to detect more cases of overlapping buffers in memcpy and
aliases to restrict-qualified parameters. While testing my new warning,
I got one result on the gnu coreutils touch.c file [1].
See the output below:
../src/touch.c: In function 'get_reldate':
../src/touch.c:115:9: warning: argument passed to 'restrict'-qualified
parameter aliases with another argument [-Wanalyzer-restrict]
115 | if (! parse_datetime (result, flex_date, now))
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
'main': events 1-8
|
| 261 | main (int argc, char **argv)
| | ^~~~
| | |
| | (1) entry to 'mai
|......
| 279 | while ((c = getopt_long (argc, argv, "acd:fhmr:t:", longopts,
NULL)) != -1)
| |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| |
|
| |
(2) following 'true' branch (when 'c != -1')...
| 280 | {
| 281 | switch (c)
| | ~~~~~~
| | |
| | (3) ...to here
|......
| 344 | if (use_ref)
| | ~
| | |
| | (4) following 'true' branch...
|......
| 349 | if (no_dereference ? lstat (ref_file, &ref_stats)
| | ~ ~
| | | |
| | | (5) ...to here
| | (6) following 'false' branch...
|......
| 353 | newtime[0] = get_stat_atime (&ref_stats);
| | ~~~~~~~~~~~~~~~~~~~~~~~~~~~
| | |
| | (7) ...to here
|......
| 356 | if (flex_date)
| | ~
| | |
| | (8) following 'true' branch (when 'flex_date' is
non-NULL)...
|
'main': events 9-12
|
| 358 | if (change_times & CH_ATIME)
| | ~ ^
| | | |
| | | (9) ...to here
| | (10) following 'true' branch...
| 359 | get_reldate (&newtime[0], flex_date, &newtime[0]);
| | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| | |
| | (11) ...to here
| | (12) calling 'get_reldate' from 'main'
|
+--> 'get_reldate': events 13-14
|
| 112 | get_reldate (struct timespec *result,
| | ^~~~~~~~~~~
| | |
| | (13) entry to 'get_reldate'
|......
| 115 | if (! parse_datetime (result, flex_date, now))
| | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| | |
| | (14) 'result' and 'now' point to the same memory
location
|
In file included from ../src/touch.c:31:
../lib/parse-datetime.h:22:6: note: declared here
22 | bool parse_datetime (struct timespec *restrict,
| ^~~~~~~~~~~~~~
My (and David's) understanding of the restrict keyword is that any read
or write to the memory location must occur through the restrict-qualified
parameter. In the case of 'parse_datetime' from gnulib, 'result' is an
output parameter, thus the function might write to 'result' before reading
'now' [2].
I'm a bit unsure, due to the bulky definition of restrict, whether this
is actually a true positive and does express what gnulib intended with
the change. So I'd like to hear your opinions on this.
- Tim
[1]
https://git.savannah.gnu.org/gitweb/?p=coreutils.git;a=blob;f=src/touch.c;h=21c247d0b10eedb615bf044ba6ea08520f3d0546;hb=HEAD#l359
[2] The function does write 'result' after the last read of 'now' and
does not use restrict in the implementation, so it should be safe
but is still somewhat undefined behavior?
