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: unassig...@gcc.gnu.org ReportedBy: sworddrag...@aol.com 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.