https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77696
--- Comment #15 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
(In reply to David Malcolm from comment #14)
Some random UI ideas (brainstorming in Emacs, so no idea if these are
*good* ideas):
warning: buffer overflow: writing 9-110 bytes into a buffer with capacity 80
[-Wformat-overflow=]
7 | __builtin_sprintf (buf, "/%s/%s-%i.tmp", tmpdir, fname, num);
| ~~~ ~~~^~~~~~~~~~
| | |
| | writing 9...110 bytes
| capacity: 80 bytes
note: details
7 | __builtin_sprintf (buf, "/%s/%s-%i.tmp", tmpdir, fname, num);
| ~~~ ab~cd~ef~g~~~h
| | || || || | |
| | || || || | 1 byte (NUL terminator)
| | || || || 4 bytes (".tmp")
| | || || |1...16 bytes ("%i" on 'num')
| | || || 1 byte ("-")
| | || |0-8 bytes ("%s" on 'fname')
| | || 1 byte ("/")
| | |0-79 bytes ("%s" on 'tmpdir')
| | 1 byte ("/")
| capacity: 80 bytes
note: layout [-fsome-option-enabling-this]
(with alternating colorization to better distinguish all those ranges and
labels)
|+---+--------------+----+-------------+-----+-----------+------+------+
start @||0 |1 |1-80|2-81 |10-89|11-90 |12-106|16-110|
size:|| 1| 0 - 79 | 1| 8| 1| 1-16???| 4| 1|
||"/"|%s on 'tmpdir'| "/"|%s on 'fname'| "-" |%i on 'num'|".tmp"| NUL |
|+---+--------------+----+-------------+-----+-----------+------+------+
or with a vertical orientation:
note: layout [-fsome-option-enabling-this]
+----------------+-----------+--------+---------------+
|element |starting at| size|cumulative size|
+----------------+-----------+--------+---------------+
|"/" | 0 | 1 | 1 |
|"%s" on 'tmpdir'| 1 | 0 - 79 | 1 - 80 |
|"/" | 1 - 80 | 1 | 2 - 81 |
|"%s" on 'fname' | 2 - 81 | 0 - 7 | 2 - 88 |
|"-" | 2 - 88 | 1 | 3 - 89 |
|"%i" on 'num' | 3 - 89 | 1- 16 | 4 - 105 |
|".tmp" | 4 - 105 | 4 | 8 - 109 |
|NUL terminator | 8 - 109 | 1 | 9 - 110 |
+----------------+-----------+--------+---------------+
(I've probably got some of the numbers wrong above, but hopefully you
get the idea of where I'm going with this).
Maybe some kind of highlight to show where we can exceed the buffer
capacity.
I like calling out the NUL terminator explicitly (as it's so easy to
get wrong), and putting "buffer overflow" upfront in the text of the
warning, as I did above.
