2021-09-03 13:52:58

by Jason Gunthorpe

Subject: [PATCH] IB/qib: Fix null pointer subtraction compiler warning

>> drivers/infiniband/hw/qib/qib_sysfs.c:411:1: warning: performing pointer subtraction with a null pointer has undefined behavior
+[-Wnull-pointer-subtraction]
QIB_DIAGC_ATTR(rc_resends);
^~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/infiniband/hw/qib/qib_sysfs.c:408:51: note: expanded from macro 'QIB_DIAGC_ATTR'
.counter = &((struct qib_ibport *)0)->rvp.n_##N - (u64 *)0, \

Use offsetof and accomplish the type check using static_assert.

Fixes: 4a7aaf88c89f ("RDMA/qib: Use attributes for the port sysfs")
Reported-by: kernel test robot <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>
---
drivers/infiniband/hw/qib/qib_sysfs.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/hw/qib/qib_sysfs.c b/drivers/infiniband/hw/qib/qib_sysfs.c
index d57e49de6650be..452e2355d24eeb 100644
--- a/drivers/infiniband/hw/qib/qib_sysfs.c
+++ b/drivers/infiniband/hw/qib/qib_sysfs.c
@@ -403,9 +403,11 @@ static ssize_t diagc_attr_store(struct ib_device *ibdev, u32 port_num,
}

#define QIB_DIAGC_ATTR(N) \
+ static_assert(&((struct qib_ibport *)0)->rvp.n_##N != (u64 *)NULL); \
static struct qib_diagc_attr qib_diagc_attr_##N = { \
.attr = __ATTR(N, 0664, diagc_attr_show, diagc_attr_store), \
- .counter = &((struct qib_ibport *)0)->rvp.n_##N - (u64 *)0, \
+ .counter = \
+ offsetof(struct qib_ibport, rvp.n_##N) / sizeof(u64) \
}

QIB_DIAGC_ATTR(rc_resends);

base-commit: 6a217437f9f5482a3f6f2dc5fcd27cf0f62409ac
--
2.33.0

2021-09-03 17:27:41

by Dennis Dalessandro

Subject: Re: [PATCH] IB/qib: Fix null pointer subtraction compiler warning

On 9/3/21 9:07 AM, Jason Gunthorpe wrote:
>>> drivers/infiniband/hw/qib/qib_sysfs.c:411:1: warning: performing pointer subtraction with a null pointer has undefined behavior
> +[-Wnull-pointer-subtraction]
> QIB_DIAGC_ATTR(rc_resends);
> ^~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/infiniband/hw/qib/qib_sysfs.c:408:51: note: expanded from macro 'QIB_DIAGC_ATTR'
> .counter = &((struct qib_ibport *)0)->rvp.n_##N - (u64 *)0, \
>
> Use offsetof and accomplish the type check using static_assert.
>
> Fixes: 4a7aaf88c89f ("RDMA/qib: Use attributes for the port sysfs")
> Reported-by: kernel test robot <[email protected]>
> Signed-off-by: Jason Gunthorpe <[email protected]>
> ---
> drivers/infiniband/hw/qib/qib_sysfs.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/infiniband/hw/qib/qib_sysfs.c b/drivers/infiniband/hw/qib/qib_sysfs.c
> index d57e49de6650be..452e2355d24eeb 100644
> --- a/drivers/infiniband/hw/qib/qib_sysfs.c
> +++ b/drivers/infiniband/hw/qib/qib_sysfs.c
> @@ -403,9 +403,11 @@ static ssize_t diagc_attr_store(struct ib_device *ibdev, u32 port_num,
> }
>
> #define QIB_DIAGC_ATTR(N) \
> + static_assert(&((struct qib_ibport *)0)->rvp.n_##N != (u64 *)NULL); \
> static struct qib_diagc_attr qib_diagc_attr_##N = { \
> .attr = __ATTR(N, 0664, diagc_attr_show, diagc_attr_store), \
> - .counter = &((struct qib_ibport *)0)->rvp.n_##N - (u64 *)0, \
> + .counter = \
> + offsetof(struct qib_ibport, rvp.n_##N) / sizeof(u64) \
> }
>
> QIB_DIAGC_ATTR(rc_resends);
>
> base-commit: 6a217437f9f5482a3f6f2dc5fcd27cf0f62409ac
>

Looks fine.

Acked-by: Dennis Dalessandro <[email protected]>

2021-09-08 12:53:56

by Jason Gunthorpe

Subject: Re: [PATCH] IB/qib: Fix null pointer subtraction compiler warning

On Fri, Sep 03, 2021 at 10:07:28AM -0300, Jason Gunthorpe wrote:
> >> drivers/infiniband/hw/qib/qib_sysfs.c:411:1: warning: performing pointer subtraction with a null pointer has undefined behavior
> +[-Wnull-pointer-subtraction]
> QIB_DIAGC_ATTR(rc_resends);
> ^~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/infiniband/hw/qib/qib_sysfs.c:408:51: note: expanded from macro 'QIB_DIAGC_ATTR'
> .counter = &((struct qib_ibport *)0)->rvp.n_##N - (u64 *)0, \
>
> Use offsetof and accomplish the type check using static_assert.
>
> Fixes: 4a7aaf88c89f ("RDMA/qib: Use attributes for the port sysfs")
> Reported-by: kernel test robot <[email protected]>
> Signed-off-by: Jason Gunthorpe <[email protected]>
> Acked-by: Dennis Dalessandro <[email protected]>
> ---
> drivers/infiniband/hw/qib/qib_sysfs.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)

Applied to for-rc

Jason