https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66373
Bug ID: 66373
Summary: gcc downloaded from Fedora 21 repository produces
defective executable. Same source code with gcc from
Fedora 19 and Fedora 20 works fine
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: juanslayton at dslextreme dot com
Target Milestone: ---
Created attachment 35675
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35675&action=edit
source code and 3 compilations from different gcc versions
In the attached files, xs.c is the source file for a program that polls 40 USB
keyboards (the “student keyboards”) and does various things with any input that
it finds. Files a, b, and c are executable files produced by 3 different
editions of gcc downloaded from Fedora repositories. Each was compiled with
“gcc -Wall -Wextra -lSDL2 -lrt -lSDL2_ttf -O3 xs.c”. Each compilation was
clean, with no errors or warnings.
Files a and b work beautifully. File c misbehaves in such a way as to render
the program unusable. Under the circumstances, suspicion falls on the latest
edition of gcc as downloaded from the Fedora 21 repository.
Here are the specifics.
File a was compiled with Fedora 19, gcc version 4.8.2 20131212 (Red Hat
4.8.2-7)
File b was compiled with Fedora 20, gcc version 4.8.3 20140911 (Red Hat
4.8.3-7)
File c was compiled with Fedora 21, gcc version 4.9.2 20150212 (Red Hat
4.9.2-6)
The failure seems to be on a return from subroutine get_event, lines 2919ff,
of xp.c This subroutine is called to read keystrokes from student boards and
return them to the calling routines. There are 7 such routines; four present
math facts drills, one gives keyboarding practice, one gives advice on written
work from a textbook, and one is a rudimentary word processor. They process
returns from get_event in various ways, but the run time error is the same for
each of them, which points to get_event as the error location. This is not a
sure thing, and it could be that whatever the error is, it could be duplicated
in each of the 7 calling routines.
The error is this, when get_event returns 10, (ie, ‘enter’ has been pushed) the
program jumps to the primary program menu, rather than continuing the routine
that called get_event. Whether it does this by going through that routine, or
by somehow going around it, I haven’t yet determined. But the fact that only
compilations under the latest gcc edition show this behavior, suggests a bug
in the compiler. I can’t imagine what it would be.
