Hi Olivier,
On 8/1/2021 11:06 AM, Eli Britstein wrote:
On 7/30/2021 2:10 PM, Olivier Matz wrote:
External email: Use caution opening links or attachments
Hi Eli,
On Thu, Jul 29, 2021 at 10:13:45AM +0300, Eli Britstein wrote:
On 7/28/2021 6:28 PM, Olivier Matz wrote:
External email: Use caution opening links or attachments
On Tue, Jul 13, 2021 at 09:49:09AM +0300, Eli Britstein wrote:
In rte_pktmbuf_mtod_offset macro, there is a casting from char *
to type
't', which may cause cast-align warning when using gcc flags
'-Werror -Wcast-align':
.../include/rte_mbuf_core.h:723:3: error: cast increases required
alignment
of target type [-Werror=cast-align]
723 | ((t)((char *)(m)->buf_addr + (m)->data_off + (o)))
| ^
As the code assumes correct alignment, add first a (void *)
casting, to
avoid the warning.
Fixes: af75078fece3 ("first public release")
Cc: sta...@dpdk.org
Signed-off-by: Eli Britstein <el...@nvidia.com>
My initial thinking was that it's the problem of the application: if
-Werror=cast-align is used, it is up to the application to cast the
return value of rte_pktmbuf_mtod_offset() to (void *) before
casting it
to the network type.
But, if I understand correctly, the problem is not about the
application
code itself, but about inlined code in the header files of dpdk
(i.e. compiling an empty C file that just includes the dpdk headers
with
-Werror=cast-align). Is it correct? If yes I think it should be
highlighted in the commit log.
I think yes, though in this specific patch it is not even an inline
function, but a macro.
However, I don't have a synthetic application example to show those
warnings, thus didn't put such in the commit msg.
For this patch, I think it would be useful to have a way to reproduce
the issue first, so we can check whether it is the proper place to fix
the problem.
--- a/examples/l2fwd/Makefile
+++ b/examples/l2fwd/Makefile
@@ -22,6 +22,7 @@ static: build/$(APP)-static
ln -sf $(APP)-static build/$(APP)
PC_FILE := $(shell $(PKGCONF) --path libdpdk 2>/dev/null)
+CFLAGS += -Wcast-align=strict
CFLAGS += -O3 $(shell $(PKGCONF) --cflags libdpdk)
gcc (Ubuntu 9.3.0-10ubuntu2) 9.3.0
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE.
make -C examples/l2fwd clean static
To reproduce locally with DPDK only, no need to change any file. Only run:
CFLAGS="-Wcast-align=strict" make V=1 -C examples/l2fwd clean static
How would you like to proceed?
Thanks,
Eli
To me, it is assumed in the DPDK project that we can mmap a network
structure on mbuf data (maybe I'm wrong?). If an external application
like OVS wants to use -Werror=cast-align, it has to cast the result of
calls to rte_pktmbuf_mtod() family.
The only corner cases are DPDK header files which have static inline
functions or macro that forces the use of rte_pktmbuf_mtod() family
without a cast (like for your patch 1/3), because it cannot be fixed in
the external project.
I think we have to make our header files compliant to projects that want
to use -Werror=cast-align, like we do to make our header files compliant
to C++.
What you suggest in this patch forces the cast to (void *) for all users
of rte_pktmbuf_mtod() family. This could be a problem for projects that
want to see these warnings.
Would it be possible instead to add a cast in DPDK headers, in inline
functions that make use of these mtod functions?
Regards,
Olivier
Out of curiosity, how did you find the errors? I mean, is it possible
that some casts are missing some other headers, or is this patchset
exhaustive?
Currently OVS-DPDK is compiled only with -Wno-cast-align.
Following complaint that a recent commit introduced a degradation in
OVS
[1], I compiled OVS without this warning deprecation.
The fixes in OVS are [2] and [3] (already merged). The fixes in DPDK
are in
this patch-set.
[1]
https://mail.openvswitch.org/pipermail/ovs-dev/2021-July/385084.html
[2]
https://mail.openvswitch.org/pipermail/ovs-dev/2021-July/386278.html
e8cccd3a3589 ("netdev-offload-dpdk: Fix IPv6 rewrite cast-align
warning.")
[3]
https://mail.openvswitch.org/pipermail/ovs-dev/2021-July/386279.html
1f7f557603a5 ("netdev-offload-dpdk: Fix vxlan vni cast-align
warnings.")
Thanks,
Olivier
---
lib/mbuf/rte_mbuf_core.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/lib/mbuf/rte_mbuf_core.h b/lib/mbuf/rte_mbuf_core.h
index bb38d7f581..dabdeee604 100644
--- a/lib/mbuf/rte_mbuf_core.h
+++ b/lib/mbuf/rte_mbuf_core.h
@@ -720,7 +720,7 @@ struct rte_mbuf_ext_shared_info {
* The type to cast the result into.
*/
#define rte_pktmbuf_mtod_offset(m, t, o) \
- ((t)((char *)(m)->buf_addr + (m)->data_off + (o)))
+ ((t)(void *)((char *)(m)->buf_addr + (m)->data_off + (o)))
/**
* A macro that points to the start of the data in the mbuf.
--
2.28.0.2311.g225365fb51
