| Message ID | 20200220062243.68809-1-keescook@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | fcntl: Distribute switch variables for initialization | expand |
On Wed, Feb 19, 2020 at 10:22:43PM -0800, Kees Cook wrote: > Variables declared in a switch statement before any case statements > cannot be automatically initialized with compiler instrumentation (as > they are not part of any execution flow). With GCC's proposed automatic > stack variable initialization feature, this triggers a warning (and they > don't get initialized). Clang's automatic stack variable initialization > (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also > doesn't initialize such variables[1]. Note that these warnings (or silent > skipping) happen before the dead-store elimination optimization phase, > so even when the automatic initializations are later elided in favor of > direct initializations, the warnings remain. > > To avoid these problems, move such variables into the "case" where > they're used or lift them up into the main function body. > > fs/fcntl.c: In function ‘send_sigio_to_task’: > fs/fcntl.c:738:20: warning: statement will never be executed [-Wswitch-unreachable] > 738 | kernel_siginfo_t si; > | ^~ > > [1] https://bugs.llvm.org/show_bug.cgi?id=44916 > > Signed-off-by: Kees Cook <keescook@chromium.org> Ping. Can someone pick this up, please? Thanks! -Kees > --- > fs/fcntl.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/fs/fcntl.c b/fs/fcntl.c > index 9bc167562ee8..2e4c0fa2074b 100644 > --- a/fs/fcntl.c > +++ b/fs/fcntl.c > @@ -735,8 +735,9 @@ static void send_sigio_to_task(struct task_struct *p, > return; > > switch (signum) { > - kernel_siginfo_t si; > - default: > + default: { > + kernel_siginfo_t si; > + > /* Queue a rt signal with the appropriate fd as its > value. We use SI_SIGIO as the source, not > SI_KERNEL, since kernel signals always get > @@ -769,6 +770,7 @@ static void send_sigio_to_task(struct task_struct *p, > si.si_fd = fd; > if (!do_send_sig_info(signum, &si, p, type)) > break; > + } > /* fall-through - fall back on the old plain SIGIO signal */ > case 0: > do_send_sig_info(SIGIO, SEND_SIG_PRIV, p, type); >
On Mon, 2020-03-02 at 20:41 -0800, Kees Cook wrote: > On Wed, Feb 19, 2020 at 10:22:43PM -0800, Kees Cook wrote: > > Variables declared in a switch statement before any case statements > > cannot be automatically initialized with compiler instrumentation (as > > they are not part of any execution flow). With GCC's proposed automatic > > stack variable initialization feature, this triggers a warning (and they > > don't get initialized). Clang's automatic stack variable initialization > > (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also > > doesn't initialize such variables[1]. Note that these warnings (or silent > > skipping) happen before the dead-store elimination optimization phase, > > so even when the automatic initializations are later elided in favor of > > direct initializations, the warnings remain. > > > > To avoid these problems, move such variables into the "case" where > > they're used or lift them up into the main function body. > > > > fs/fcntl.c: In function ‘send_sigio_to_task’: > > fs/fcntl.c:738:20: warning: statement will never be executed [-Wswitch-unreachable] > > 738 | kernel_siginfo_t si; > > | ^~ > > > > [1] https://bugs.llvm.org/show_bug.cgi?id=44916 > > > > Signed-off-by: Kees Cook <keescook@chromium.org> > > Ping. Can someone pick this up, please? > > Thanks! > > -Kees > > > --- > > fs/fcntl.c | 6 ++++-- > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > diff --git a/fs/fcntl.c b/fs/fcntl.c > > index 9bc167562ee8..2e4c0fa2074b 100644 > > --- a/fs/fcntl.c > > +++ b/fs/fcntl.c > > @@ -735,8 +735,9 @@ static void send_sigio_to_task(struct task_struct *p, > > return; > > > > switch (signum) { > > - kernel_siginfo_t si; > > - default: > > + default: { > > + kernel_siginfo_t si; > > + > > /* Queue a rt signal with the appropriate fd as its > > value. We use SI_SIGIO as the source, not > > SI_KERNEL, since kernel signals always get > > @@ -769,6 +770,7 @@ static void send_sigio_to_task(struct task_struct *p, > > si.si_fd = fd; > > if (!do_send_sig_info(signum, &si, p, type)) > > break; > > + } > > /* fall-through - fall back on the old plain SIGIO signal */ > > case 0: > > do_send_sig_info(SIGIO, SEND_SIG_PRIV, p, type); > > Sure, looks straightforward enough. I'll pick it up for v5.7. Thanks,
On Tue, Mar 03, 2020 at 10:55:22AM -0500, Jeff Layton wrote: > On Mon, 2020-03-02 at 20:41 -0800, Kees Cook wrote: > > On Wed, Feb 19, 2020 at 10:22:43PM -0800, Kees Cook wrote: > > > Variables declared in a switch statement before any case statements > > > cannot be automatically initialized with compiler instrumentation (as > > > they are not part of any execution flow). With GCC's proposed automatic > > > stack variable initialization feature, this triggers a warning (and they > > > don't get initialized). Clang's automatic stack variable initialization > > > (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also > > > doesn't initialize such variables[1]. Note that these warnings (or silent > > > skipping) happen before the dead-store elimination optimization phase, > > > so even when the automatic initializations are later elided in favor of > > > direct initializations, the warnings remain. > > > > > > To avoid these problems, move such variables into the "case" where > > > they're used or lift them up into the main function body. > > > > > > fs/fcntl.c: In function ‘send_sigio_to_task’: > > > fs/fcntl.c:738:20: warning: statement will never be executed [-Wswitch-unreachable] > > > 738 | kernel_siginfo_t si; > > > | ^~ > > > > > > [1] https://bugs.llvm.org/show_bug.cgi?id=44916 > > > > > > Signed-off-by: Kees Cook <keescook@chromium.org> > > > > Ping. Can someone pick this up, please? > > > > Thanks! > > > > -Kees > > > > > --- > > > fs/fcntl.c | 6 ++++-- > > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > > > diff --git a/fs/fcntl.c b/fs/fcntl.c > > > index 9bc167562ee8..2e4c0fa2074b 100644 > > > --- a/fs/fcntl.c > > > +++ b/fs/fcntl.c > > > @@ -735,8 +735,9 @@ static void send_sigio_to_task(struct task_struct *p, > > > return; > > > > > > switch (signum) { > > > - kernel_siginfo_t si; > > > - default: > > > + default: { > > > + kernel_siginfo_t si; > > > + > > > /* Queue a rt signal with the appropriate fd as its > > > value. We use SI_SIGIO as the source, not > > > SI_KERNEL, since kernel signals always get > > > @@ -769,6 +770,7 @@ static void send_sigio_to_task(struct task_struct *p, > > > si.si_fd = fd; > > > if (!do_send_sig_info(signum, &si, p, type)) > > > break; > > > + } > > > /* fall-through - fall back on the old plain SIGIO signal */ > > > case 0: > > > do_send_sig_info(SIGIO, SEND_SIG_PRIV, p, type); > > > > > Sure, looks straightforward enough. I'll pick it up for v5.7. Awesome; thank you! -Kees > > Thanks, > -- > Jeff Layton <jlayton@kernel.org> >
diff --git a/fs/fcntl.c b/fs/fcntl.c index 9bc167562ee8..2e4c0fa2074b 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -735,8 +735,9 @@ static void send_sigio_to_task(struct task_struct *p, return; switch (signum) { - kernel_siginfo_t si; - default: + default: { + kernel_siginfo_t si; + /* Queue a rt signal with the appropriate fd as its value. We use SI_SIGIO as the source, not SI_KERNEL, since kernel signals always get @@ -769,6 +770,7 @@ static void send_sigio_to_task(struct task_struct *p, si.si_fd = fd; if (!do_send_sig_info(signum, &si, p, type)) break; + } /* fall-through - fall back on the old plain SIGIO signal */ case 0: do_send_sig_info(SIGIO, SEND_SIG_PRIV, p, type);
Variables declared in a switch statement before any case statements cannot be automatically initialized with compiler instrumentation (as they are not part of any execution flow). With GCC's proposed automatic stack variable initialization feature, this triggers a warning (and they don't get initialized). Clang's automatic stack variable initialization (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also doesn't initialize such variables[1]. Note that these warnings (or silent skipping) happen before the dead-store elimination optimization phase, so even when the automatic initializations are later elided in favor of direct initializations, the warnings remain. To avoid these problems, move such variables into the "case" where they're used or lift them up into the main function body. fs/fcntl.c: In function ‘send_sigio_to_task’: fs/fcntl.c:738:20: warning: statement will never be executed [-Wswitch-unreachable] 738 | kernel_siginfo_t si; | ^~ [1] https://bugs.llvm.org/show_bug.cgi?id=44916 Signed-off-by: Kees Cook <keescook@chromium.org> --- fs/fcntl.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)