ipc: fix trivial warning
in [Kernel]
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From: Jiri Kosina on 19 Oct 2009 10:20 On Mon, 19 Oct 2009, Felipe Contreras wrote: > Commit a0d092f introduced the following warning: > ipc/msg.c: In function ?msgctl_down?: > ipc/msg.c:415: warning: ?msqid64? may be used uninitialized in this function > > Signed-off-by: Felipe Contreras <felipe.contreras(a)gmail.com> > --- > ipc/msg.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/ipc/msg.c b/ipc/msg.c > index 2ceab7f..085bd58 100644 > --- a/ipc/msg.c > +++ b/ipc/msg.c > @@ -412,7 +412,7 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd, > struct msqid_ds __user *buf, int version) > { > struct kern_ipc_perm *ipcp; > - struct msqid64_ds msqid64; > + struct msqid64_ds uninitialized_var(msqid64); > struct msg_queue *msq; > int err; What gcc are you using? I am not getting any warning at least with gcc "(SUSE Linux) 4.3.1 20080507 (prerelease) [gcc-4_3-branch revision 135036]" $ make ipc/msg.o CHK include/linux/version.h CHK include/linux/utsrelease.h SYMLINK include/asm -> include/asm-x86 CALL scripts/checksyscalls.sh CC ipc/msg.o $ -- Jiri Kosina SUSE Labs, Novell Inc. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Jiri Kosina on 19 Oct 2009 11:00 On Mon, 19 Oct 2009, Felipe Contreras wrote: > >> ipc/msg.c: In function ?msgctl_down?: > >> ipc/msg.c:415: warning: ?msqid64? may be used uninitialized in this function > >> > >> Signed-off-by: Felipe Contreras <felipe.contreras(a)gmail.com> > >> --- > >> ipc/msg.c | 2 +- > >> 1 files changed, 1 insertions(+), 1 deletions(-) > >> > >> diff --git a/ipc/msg.c b/ipc/msg.c > >> index 2ceab7f..085bd58 100644 > >> --- a/ipc/msg.c > >> +++ b/ipc/msg.c > >> @@ -412,7 +412,7 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd, > >> struct msqid_ds __user *buf, int version) > >> { > >> struct kern_ipc_perm *ipcp; > >> - struct msqid64_ds msqid64; > >> + struct msqid64_ds uninitialized_var(msqid64); > >> struct msg_queue *msq; > >> int err; > > > > What gcc are you using? I am not getting any warning at least with gcc > > "(SUSE Linux) 4.3.1 20080507 (prerelease) [gcc-4_3-branch revision > > 135036]" > > gcc (GCC) 4.4.1 20090725 (Red Hat 4.4.1-2) > > Since I moved to Fedora 11 I get more warnings than other people, > possibly because gcc 4.4. Wouldn't it be better just to report this to gcc developers as a bug instead? I have verified both with 4.1 and 4.3, and it doesn't emit this false-positive warning, so there have been gcc versions getting this right. Ergo gcc developers should rather fix this "regression" and revert to the old behavior, methinks. -- Jiri Kosina SUSE Labs, Novell Inc.
From: Felipe Contreras on 19 Oct 2009 11:00 On Mon, Oct 19, 2009 at 5:12 PM, Jiri Kosina <jkosina(a)suse.cz> wrote: > On Mon, 19 Oct 2009, Felipe Contreras wrote: > >> Commit a0d092f introduced the following warning: >> ipc/msg.c: In function ?msgctl_down?: >> ipc/msg.c:415: warning: ?msqid64? may be used uninitialized in this function >> >> Signed-off-by: Felipe Contreras <felipe.contreras(a)gmail.com> >> --- >> ipc/msg.c | 2 +- >> 1 files changed, 1 insertions(+), 1 deletions(-) >> >> diff --git a/ipc/msg.c b/ipc/msg.c >> index 2ceab7f..085bd58 100644 >> --- a/ipc/msg.c >> +++ b/ipc/msg.c >> @@ -412,7 +412,7 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd, >> struct msqid_ds __user *buf, int version) >> { >> struct kern_ipc_perm *ipcp; >> - struct msqid64_ds msqid64; >> + struct msqid64_ds uninitialized_var(msqid64); >> struct msg_queue *msq; >> int err; > > What gcc are you using? I am not getting any warning at least with gcc > "(SUSE Linux) 4.3.1 20080507 (prerelease) [gcc-4_3-branch revision > 135036]" gcc (GCC) 4.4.1 20090725 (Red Hat 4.4.1-2) Since I moved to Fedora 11 I get more warnings than other people, possibly because gcc 4.4. -- Felipe Contreras -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Jiri Kosina on 19 Oct 2009 11:30 On Mon, 19 Oct 2009, Felipe Contreras wrote: > >> >> ipc/msg.c: In function ?msgctl_down?: > >> >> ipc/msg.c:415: warning: ?msqid64? may be used uninitialized in this function > >> >> > >> >> Signed-off-by: Felipe Contreras <felipe.contreras(a)gmail.com> > >> >> --- > >> >> ipc/msg.c | 2 +- > >> >> 1 files changed, 1 insertions(+), 1 deletions(-) > >> >> > >> >> diff --git a/ipc/msg.c b/ipc/msg.c > >> >> index 2ceab7f..085bd58 100644 > >> >> --- a/ipc/msg.c > >> >> +++ b/ipc/msg.c > >> >> @@ -412,7 +412,7 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd, > >> >> struct msqid_ds __user *buf, int version) > >> >> { > >> >> struct kern_ipc_perm *ipcp; > >> >> - struct msqid64_ds msqid64; > >> >> + struct msqid64_ds uninitialized_var(msqid64); > >> >> struct msg_queue *msq; > >> >> int err; [ ... snip ... ] > > I have verified both with 4.1 and 4.3, and it doesn't emit this > > false-positive warning, so there have been gcc versions getting this > > right. Ergo gcc developers should rather fix this "regression" and revert > > to the old behavior, methinks. > > The other possibility is that the bug was in gcc 4.1/4.3, and now 4.4 > finds an actual problem in the code. I will try to dig deeper to see > what's actually happening... at first glance I don't see who is > initializing msqid64. This statement of your makes me wonder why you have submitted the patch in the first place, as you are apparently not sure whether adding uninitialized_var() is a valid thing to do or not. The gcc warning in this case is actually bogus, as msqid64 is touched only iff cmd == IPC_SET, and in such case, copy_msqid_from_user() initializes it properly. -- Jiri Kosina SUSE Labs, Novell Inc.
From: Felipe Contreras on 19 Oct 2009 11:30 On Mon, Oct 19, 2009 at 5:57 PM, Jiri Kosina <jkosina(a)suse.cz> wrote: > On Mon, 19 Oct 2009, Felipe Contreras wrote: > >> >> ipc/msg.c: In function ?msgctl_down?: >> >> ipc/msg.c:415: warning: ?msqid64? may be used uninitialized in this function >> >> >> >> Signed-off-by: Felipe Contreras <felipe.contreras(a)gmail.com> >> >> --- >> >> ipc/msg.c | 2 +- >> >> 1 files changed, 1 insertions(+), 1 deletions(-) >> >> >> >> diff --git a/ipc/msg.c b/ipc/msg.c >> >> index 2ceab7f..085bd58 100644 >> >> --- a/ipc/msg.c >> >> +++ b/ipc/msg.c >> >> @@ -412,7 +412,7 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd, >> >> struct msqid_ds __user *buf, int version) >> >> { >> >> struct kern_ipc_perm *ipcp; >> >> - struct msqid64_ds msqid64; >> >> + struct msqid64_ds uninitialized_var(msqid64); >> >> struct msg_queue *msq; >> >> int err; >> > >> > What gcc are you using? I am not getting any warning at least with gcc >> > "(SUSE Linux) 4.3.1 20080507 (prerelease) [gcc-4_3-branch revision >> > 135036]" >> >> gcc (GCC) 4.4.1 20090725 (Red Hat 4.4.1-2) >> >> Since I moved to Fedora 11 I get more warnings than other people, >> possibly because gcc 4.4. > > Wouldn't it be better just to report this to gcc developers as a bug > instead? If it's a gcc bug, yes. > I have verified both with 4.1 and 4.3, and it doesn't emit this > false-positive warning, so there have been gcc versions getting this > right. Ergo gcc developers should rather fix this "regression" and revert > to the old behavior, methinks. The other possibility is that the bug was in gcc 4.1/4.3, and now 4.4 finds an actual problem in the code. I will try to dig deeper to see what's actually happening... at first glance I don't see who is initializing msqid64. -- Felipe Contreras -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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