Hi On Mon, Nov 3, 2014 at 1:44 PM, Zbigniew Jędrzejewski-Szmek <zbys...@in.waw.pl> wrote: > On Mon, Nov 03, 2014 at 01:41:20PM +0100, Lennart Poettering wrote: >> On Mon, 03.11.14 13:12, David Herrmann (dh.herrm...@gmail.com) wrote: >> >> > Hi >> > >> > On Thu, Oct 16, 2014 at 11:43 PM, <philippedesw...@gmail.com> wrote: >> > > From: Philippe De Swert <philippedesw...@gmail.com> >> > > >> > > Remove the following warning during the compilation: >> > > src/libsystemd-terminal/grdev-drm.c: In function 'grdrm_card_hotplug': >> > > src/libsystemd-terminal/grdev-drm.c:1087:45: warning: 'fb' may be used >> > > uninitialized in this function [-Wmaybe-uninitialized] >> > > src/libsystemd-terminal/grdev-drm.c:1035:19: note: 'fb' was declared here >> > > --- >> > > src/libsystemd-terminal/grdev-drm.c | 2 +- >> > > 1 file changed, 1 insertion(+), 1 deletion(-) >> > > >> > > diff --git a/src/libsystemd-terminal/grdev-drm.c >> > > b/src/libsystemd-terminal/grdev-drm.c >> > > index dba6db2..415755e 100644 >> > > --- a/src/libsystemd-terminal/grdev-drm.c >> > > +++ b/src/libsystemd-terminal/grdev-drm.c >> > > @@ -1032,7 +1032,7 @@ error: >> > > >> > > static void grdrm_crtc_expose(grdrm_crtc *crtc) { >> > > grdrm_pipe *pipe; >> > > - grdrm_fb *fb; >> > > + grdrm_fb *fb = NULL; >> > >> > Ewww, this is not nice. It does fix the warning, indeed, but the >> > underlying problem is more generic. Lets look at this: >> > >> > int some_function(void **out) { >> > ... >> > r = ioctl(...); >> > if (r < 0) >> > return -errno; >> > ... >> > } >> > >> > gcc has no guarantee that "errno" is <0 if r is <0. Therefore, >> > whenever it inlines those functions (-O2 etc.), it will spew a warning >> > that "out" might be uninitialized if r<0 but errno==0. With -O0 gcc >> > doesn't complain as it probably does not optimize across functions. >> > However, with -O2 I get those warnings for "static" functions all the >> > time. >> > >> > Not sure what to do here. I dislike initializing the pointer to NULL >> > as it might hide other real warnings. I'd prefer something like: >> > >> > r = -SANE_ERRNO; >> > >> > with: >> > >> > #define SANE_ERRNO (abs(errno) ? : EMAGIC) >> > >> > ...not sure what we do in other places, though. Lennart? Tom? >> >> So far we went the simple way out and merged patches like the original >> one you are replying to. >> >> Adding a call like this would make sane to me though: >> >> static inline negative_errno(void) { >> return _likely_(errno > 0) ? -errno : -EINVAL; >> } >> >> Which is then invoked as: >> >> return negative_errno(); >> >> or so... > I like the assert more, because having errno <= 0 would be a signficant bug > in the system, not something that we want to ever hide. So basically this > is a way to tell the compiler what we already know, and assert is better.
Indeed. So how about: static inline int negative_errno(void) { assert_return(errno > 0, -EINVAL); return -errno; } Thanks David > I also filed https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61846, but > without much response so far. > > Zbyszek _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel