| Message ID | 20190718141652.3323402-1-arnd@arndb.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | media: vivid: work around high stack usage with clang | expand |
On Thu, Jul 18, 2019 at 7:16 AM Arnd Bergmann <arnd@arndb.de> wrote: > > Building a KASAN-enabled kernel with clang ends up in a case where too > much is inlined into vivid_thread_vid_cap() and the stack usage grows > a lot, possibly when the register allocation fails to produce efficient > code and spills a lot of temporaries to the stack. This uses more > than twice the amount of stack than the sum of the individual functions > when they are not inlined: > > drivers/media/platform/vivid/vivid-kthread-cap.c:766:12: error: stack frame size of 2208 bytes in function 'vivid_thread_vid_cap' [-Werror,-Wframe-larger-than=] > > Marking two of the key functions in here as 'noinline_for_stack' avoids > the pathological case in clang without any apparent downside for gcc. Thanks for the patch, should be one less warning for CI. Acked-by: Nick Desaulniers <ndesaulniers@google.com> > > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > --- > Not sure how much effort we want to put into fixing clang to not > get into this case. I could open an llvm bug report if something > thinks this has a chance of getting fixed there. > --- > drivers/media/platform/vivid/vivid-kthread-cap.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/drivers/media/platform/vivid/vivid-kthread-cap.c b/drivers/media/platform/vivid/vivid-kthread-cap.c > index 6cf495a7d5cc..4f94897e6303 100644 > --- a/drivers/media/platform/vivid/vivid-kthread-cap.c > +++ b/drivers/media/platform/vivid/vivid-kthread-cap.c > @@ -232,8 +232,8 @@ static void *plane_vaddr(struct tpg_data *tpg, struct vivid_buffer *buf, > return vbuf; > } > > -static int vivid_copy_buffer(struct vivid_dev *dev, unsigned p, u8 *vcapbuf, > - struct vivid_buffer *vid_cap_buf) > +static noinline_for_stack int vivid_copy_buffer(struct vivid_dev *dev, unsigned p, > + u8 *vcapbuf, struct vivid_buffer *vid_cap_buf) > { > bool blank = dev->must_blank[vid_cap_buf->vb.vb2_buf.index]; > struct tpg_data *tpg = &dev->tpg; > @@ -670,7 +670,8 @@ static void vivid_cap_update_frame_period(struct vivid_dev *dev) > dev->cap_frame_period = f_period; > } > > -static void vivid_thread_vid_cap_tick(struct vivid_dev *dev, int dropped_bufs) > +static noinline_for_stack void vivid_thread_vid_cap_tick(struct vivid_dev *dev, > + int dropped_bufs) > { > struct vivid_buffer *vid_cap_buf = NULL; > struct vivid_buffer *vbi_cap_buf = NULL; > -- > 2.20.0 > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20190718141652.3323402-1-arnd%40arndb.de.
diff --git a/drivers/media/platform/vivid/vivid-kthread-cap.c b/drivers/media/platform/vivid/vivid-kthread-cap.c index 6cf495a7d5cc..4f94897e6303 100644 --- a/drivers/media/platform/vivid/vivid-kthread-cap.c +++ b/drivers/media/platform/vivid/vivid-kthread-cap.c @@ -232,8 +232,8 @@ static void *plane_vaddr(struct tpg_data *tpg, struct vivid_buffer *buf, return vbuf; } -static int vivid_copy_buffer(struct vivid_dev *dev, unsigned p, u8 *vcapbuf, - struct vivid_buffer *vid_cap_buf) +static noinline_for_stack int vivid_copy_buffer(struct vivid_dev *dev, unsigned p, + u8 *vcapbuf, struct vivid_buffer *vid_cap_buf) { bool blank = dev->must_blank[vid_cap_buf->vb.vb2_buf.index]; struct tpg_data *tpg = &dev->tpg; @@ -670,7 +670,8 @@ static void vivid_cap_update_frame_period(struct vivid_dev *dev) dev->cap_frame_period = f_period; } -static void vivid_thread_vid_cap_tick(struct vivid_dev *dev, int dropped_bufs) +static noinline_for_stack void vivid_thread_vid_cap_tick(struct vivid_dev *dev, + int dropped_bufs) { struct vivid_buffer *vid_cap_buf = NULL; struct vivid_buffer *vbi_cap_buf = NULL;
Building a KASAN-enabled kernel with clang ends up in a case where too much is inlined into vivid_thread_vid_cap() and the stack usage grows a lot, possibly when the register allocation fails to produce efficient code and spills a lot of temporaries to the stack. This uses more than twice the amount of stack than the sum of the individual functions when they are not inlined: drivers/media/platform/vivid/vivid-kthread-cap.c:766:12: error: stack frame size of 2208 bytes in function 'vivid_thread_vid_cap' [-Werror,-Wframe-larger-than=] Marking two of the key functions in here as 'noinline_for_stack' avoids the pathological case in clang without any apparent downside for gcc. Signed-off-by: Arnd Bergmann <arnd@arndb.de> --- Not sure how much effort we want to put into fixing clang to not get into this case. I could open an llvm bug report if something thinks this has a chance of getting fixed there. --- drivers/media/platform/vivid/vivid-kthread-cap.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)