http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55892
Bug #: 55892
Summary: Bogus compiler warning
Classification: Unclassified
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: [email protected]
ReportedBy: [email protected]
Created attachment 29092
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29092
Example code
In the attachments is the example file for this bug report. Compiling it with
"gcc -O3 -Wall -Wextra -o /dev/null -pedantic test.c" will result in a warning:
In file included from /usr/include/stdio.h:937:0,
from test.c:2:
In function 'fgets',
inlined from 'main' at test.c:17:11:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:261:2: warning: call to
'__fgets_chk_warn' declared with attribute warning: fgets called with bigger
size than length of destination buffer [enabled by default]
There are 2 potential errors on this behavior:
- If the warning triggers on line 33 it should also be triggered on all 4
lines.
- In this code the limit of fgets can never exceed a length of 8. The compiler
thinks because read_limit can be 2147483647 (INT32_MAX) limit in fgets can it
be too (which as already said can never happen in this code). Removing the 3
lines which assign INT32_MAX removes the compiler warning.
I have a suggestion for a solution:
- Like conditional return values the compiler could check if the code has a
fixed construct which makes it possible to calculate if the limit will be
exceeded (this would match on the example code and trigger no compiler
warnings). If the code has a dynamic construct which makes it not possible to
calculate if the limit would be exceeded a comiler warning is thrown.
