netdev - [PATCH] [v2] ethtool: reduce stack usage with clang

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Date:   Thu,  7 Mar 2019 16:58:35 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jiri Pirko <jiri@...lanox.com>, Wenwen Wang <wang6495@....edu>,
        Michal Kubecek <mkubecek@...e.cz>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] [v2] ethtool: reduce stack usage with clang

clang inlines the dev_ethtool() more aggressively than gcc does, leading
to a larger amount of used stack space:

net/core/ethtool.c:2536:24: error: stack frame size of 1216 bytes in function 'dev_ethtool' [-Werror,-Wframe-larger-than=]

Marking the sub-functions that require the most stack space as
noinline_for_stack gives us reasonable behavior on all compilers.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
v2: don't annotate dev_ethtool itself, as pointed out by Michal Kubecek
---
 net/core/ethtool.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/net/core/ethtool.c b/net/core/ethtool.c
index d4918ffddda8..b1eb32419732 100644
--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c
@@ -2319,9 +2319,10 @@ static int ethtool_set_tunable(struct net_device *dev, void __user *useraddr)
 	return ret;
 }
 
-static int ethtool_get_per_queue_coalesce(struct net_device *dev,
-					  void __user *useraddr,
-					  struct ethtool_per_queue_op *per_queue_opt)
+static noinline_for_stack int
+ethtool_get_per_queue_coalesce(struct net_device *dev,
+			       void __user *useraddr,
+			       struct ethtool_per_queue_op *per_queue_opt)
 {
 	u32 bit;
 	int ret;
@@ -2349,9 +2350,10 @@ static int ethtool_get_per_queue_coalesce(struct net_device *dev,
 	return 0;
 }
 
-static int ethtool_set_per_queue_coalesce(struct net_device *dev,
-					  void __user *useraddr,
-					  struct ethtool_per_queue_op *per_queue_opt)
+static noinline_for_stack int
+ethtool_set_per_queue_coalesce(struct net_device *dev,
+			       void __user *useraddr,
+			       struct ethtool_per_queue_op *per_queue_opt)
 {
 	u32 bit;
 	int i, ret = 0;
@@ -2405,7 +2407,7 @@ static int ethtool_set_per_queue_coalesce(struct net_device *dev,
 	return ret;
 }
 
-static int ethtool_set_per_queue(struct net_device *dev,
+static int noinline_for_stack ethtool_set_per_queue(struct net_device *dev,
 				 void __user *useraddr, u32 sub_cmd)
 {
 	struct ethtool_per_queue_op per_queue_opt;
-- 
2.20.0