[ovs-dev] [PATCH 1/5] datapath: hide clang frame-overflow warnings

Greg Rose gvrose8192 at gmail.com
Wed Oct 9 21:22:10 UTC 2019


From: Arnd Bergmann <arnd at arndb.de>

Upstream commit:
    commit 260637903f47f20c5918bb5c1eea52b2a28ea863
    Author: Arnd Bergmann <arnd at arndb.de>
    Date:   Mon Jul 22 17:00:01 2019 +0200

    ovs: datapath: hide clang frame-overflow warnings

    Some functions in the datapath code are factored out so that each
    one has a stack frame smaller than 1024 bytes with gcc. However,
    when compiling with clang, the functions are inlined more aggressively
    and combined again so we get

    net/openvswitch/datapath.c:1124:12: error: stack frame size of 1528 bytes in function 'ovs_flow_cmd_set' [-Werror,-Wframe-larger-than=]

    Marking both get_flow_actions() and ovs_nla_init_match_and_action()
    as 'noinline_for_stack' gives us the same behavior that we see with
    gcc, and no warning. Note that this does not mean we actually use
    less stack, as the functions call each other, and we still get
    three copies of the large 'struct sw_flow_key' type on the stack.

    The comment tells us that this was previously considered safe,
    presumably since the netlink parsing functions are called with
    a known backchain that does not also use a lot of stack space.

    Fixes: 9cc9a5cb176c ("datapath: Avoid using stack larger than 1024.")
    Signed-off-by: Arnd Bergmann <arnd at arndb.de>
    Signed-off-by: David S. Miller <davem at davemloft.net>

Cc: Arnd Bergmann <arnd at arndb.de>
Signed-off-by: Greg Rose <gvrose8192 at gmail.com>
---
 datapath/datapath.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/datapath/datapath.c b/datapath/datapath.c
index 94e4f6f..15af156 100644
--- a/datapath/datapath.c
+++ b/datapath/datapath.c
@@ -1069,7 +1069,7 @@ error:
 }
 
 /* Factor out action copy to avoid "Wframe-larger-than=1024" warning. */
-static struct sw_flow_actions *get_flow_actions(struct net *net,
+static noinline_for_stack struct sw_flow_actions *get_flow_actions(struct net *net,
 						const struct nlattr *a,
 						const struct sw_flow_key *key,
 						const struct sw_flow_mask *mask,
@@ -1103,12 +1103,13 @@ static struct sw_flow_actions *get_flow_actions(struct net *net,
  * we should not to return match object with dangling reference
  * to mask.
  * */
-static int ovs_nla_init_match_and_action(struct net *net,
-					 struct sw_flow_match *match,
-					 struct sw_flow_key *key,
-					 struct nlattr **a,
-					 struct sw_flow_actions **acts,
-					 bool log)
+static noinline_for_stack int
+ovs_nla_init_match_and_action(struct net *net,
+			      struct sw_flow_match *match,
+			      struct sw_flow_key *key,
+			      struct nlattr **a,
+			      struct sw_flow_actions **acts,
+			      bool log)
 {
 	struct sw_flow_mask mask;
 	int error = 0;
-- 
1.8.3.1



More information about the dev mailing list