https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97628
Bug ID: 97628
Summary: format truncation false positive for O1 and
mtune=nocona
Product: gcc
Version: 9.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: walter.gcc at wjd dot nu
Target Milestone: ---
Created attachment 49468
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49468&action=edit
trimmed down problem from Asterisk say.c
Per the discussion here:
https://gerrit.asterisk.org/c/asterisk/+/14501
I believe there is a bug in gcc 9 where it falsely reports:
warning: ‘%d’ directive output may be truncated writing
between 1 and 11 bytes into a region of size 10
[-Wformat-truncation=]
See the attached example, it only triggers when:
- optimization is 1 or higher
- arch tuning is set to nocona
Example:
$ gcc -O1 -mtune=nocona -S -Wall say2.c
say2.c: In function ‘ast_say_number_full_zh’:
say2.c:37:32: warning: ‘%d’ directive output may be truncated writing between 1
and 11 bytes into a region of size 10 [-Wformat-truncation=]
37 | snprintf(buf, 10, "%d", num);
| ^~
say2.c:37:31: note: directive argument in the range [-2147483648, 9]
...
But when omitting either -O1 or -mtune=nocona we do not get this warning.
And if you read the code, you would see that at line 37, num cannot be negative
(because it would've hit a different if-branch).
gcc version is the Ubuntu/Focal one:
$ gcc --version
gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
Cheers,
Walter Doekes
OSSO B.V.
