** Description changed:
+ Problem:
+ qjoypad 4.3.1-3.1 FTBFS on ppc64el (and under -O3 + LTO) in Ubuntu 26.10
(stonking) due to -Werror=maybe-uninitialized in Axis::move(): when mode !=
Keyboard and press == false, FakeEvent e was never initialized before passing
to sendevent().
+
+ Root Cause & Fix:
+ Fix the uninitialized read in src/axis.cpp as requested by adding an early
return for release in mouse modes (since mouse motion has no release action)
and value-initializing FakeEvent e{}. No compiler warnings were silenced and
LTO optimization flags were kept intact.
+
+ Verification:
+ 1. Reproduce on unmodified 4.3.1-3.1: build with -O3 -flto=auto
-ffat-lto-objects reproduces the exact error:
+ 'error: ‘MEM <unsigned int> [(struct FakeEvent *)&e]’ may be used
uninitialized [-Werror=maybe-uninitialized]'
+ 2. Verify with debdiff: full build completes with exit code 0, linking
qjoypad executable cleanly under -O3 + LTO with 0 warnings/errors.
+ 3. Verified in PPA: ppc64el build succeeded cleanly
(https://launchpad.net/~steelf/+archive/ubuntu/ppa/+build/33834461).
+
+ Upstream: https://github.com/panzi/qjoypad
+
+
+ --- [ Original Report ]
+
qjoypad 4.3.1-3.1 has been stuck in stonking-proposed for ~346 days.
update_excuses reports:
missing build on ppc64el: qjoypad (from 4.3.1-3build2)
All other architectures built fine. Build log (ppc64el):
https://launchpad.net/ubuntu/+source/qjoypad/4.3.1-3.1/+build/32794460
Failure (at LTO link time):
In function 'sendevent',
inlined from 'move' at /usr/src/qjoypad-4.3.1-3.1/src/axis.cpp:436:11:
/usr/src/qjoypad-4.3.1-3.1/src/event.cpp:8:5: error: 'MEM <unsigned int>
[(struct FakeEvent *)&e]' may be used uninitialized
[-Werror=maybe-uninitialized]
src/axis.cpp:355:15: note: 'MEM <unsigned int> [(struct FakeEvent *)&e]'
was declared here
lto1: all warnings being treated as errors
lto-wrapper: fatal error: make returned 2 exit status
Cause:
- Upstream's CMakeLists.txt builds with -Wall -Wextra -Werror (line 43).
- On ppc64el Ubuntu builds with -O3 and LTO (-flto=auto -ffat-lto-objects) by
default. With LTO, sendevent() (event.cpp) gets inlined into Axis::move()
(axis.cpp), and gcc-15 can now see that e.type may be read uninitialized, which
-Werror makes fatal. Debian has neither -O3 on ppc64el nor LTO by default, so
it builds there (Debian has ppc64el binaries of 4.3.1-3.1). The ppc64el build
of 4.3.1-3build2 in stonking predates gcc-15.
This looks like a real (minor) bug rather than a pure false positive. In
Axis::move() (src/axis.cpp ~354-437):
void Axis::move( bool press ) {
FakeEvent e;
if (mode == Keyboard) {
... // sets e.type and e.keycode
}
else if (press) {
... // sets e.type = MouseMove and e.move.{x,y}
}
//actually create the event
sendevent(e);
}
When the axis is in a mouse mode and press == false, e is never
initialised, and sendevent() reads e.type (switch (e.type) in
event.cpp:8).
Debian / upstream status:
- No open Debian bug for this (it doesn't reproduce in Debian's default
flags).
- Upstream (https://github.com/panzi/qjoypad) is largely inactive; 4.3.1 is
the latest release.
Suggested direction (to be done by whoever picks this up):
- Fix the code rather than silencing the warning: e.g. return early from
Axis::move() in the mouse-mode/release case (there is nothing to send), or at
least value-initialise the event (FakeEvent e{}; or memset) so that sendevent()
takes no action on an all-zero event. Check what the right behaviour is: with e
zeroed, type would be KeyUp with keycode 0, which sendevent() already ignores
("if (e.keycode == 0) return;"), so FakeEvent e{} is a safe minimal fix; an
early return is cleaner.
- Alternatives (less preferred): add -Wno-error=maybe-uninitialized, or
DEB_BUILD_MAINT_OPTIONS += optimize=-lto.
- Test-build on ppc64el (PPA, or a ppc64el chroot), upload as an Ubuntu
delta, and forward the patch to Debian (and upstream) since the uninitialised
read is real on all architectures.
** Changed in: qjoypad (Ubuntu)
Status: New => Confirmed
** Tags added: patch stonking
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https://bugs.launchpad.net/bugs/2170324
Title:
qjoypad FTBFS on ppc64el in stonking: -Werror=maybe-uninitialized in
Axis::move() with -O3 + LTO
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