[PATCH net-next 1/2] net: add EXPORT_INDIRECT_CALLABLE wrapper

When a static function is annotated with INDIRECT_CALLABLE_SCOPE and
CONFIG_RETPOLINE is set, the static keyword is removed. Sometimes the
function needs to be exported but EXPORT_SYMBOL can't be used because if
CONFIG_RETPOLINE is not set, we will attempt to export a static symbol.

This patch introduces a new indirect call wrapper:
EXPORT_INDIRECT_CALLABLE. This basically does EXPORT_SYMBOL when
CONFIG_RETPOLINE is set, but does nothing when it's not.

Reported-by: Stephen Rothwell <redacted>
Signed-off-by: Brian Vazquez <redacted>
---
 include/linux/indirect_call_wrapper.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/indirect_call_wrapper.h b/include/linux/indirect_call_wrapper.h
index 54c02c84906a..a8345c8a613d 100644
--- a/include/linux/indirect_call_wrapper.h
+++ b/include/linux/indirect_call_wrapper.h

@@ -36,6 +36,7 @@
 
 #define INDIRECT_CALLABLE_DECLARE(f)	f
 #define INDIRECT_CALLABLE_SCOPE
+#define EXPORT_INDIRECT_CALLABLE(f)	EXPORT_SYMBOL(f)
 
 #else
 #define INDIRECT_CALL_1(f, f1, ...) f(__VA_ARGS__)

@@ -44,6 +45,7 @@
 #define INDIRECT_CALL_4(f, f4, f3, f2, f1, ...) f(__VA_ARGS__)
 #define INDIRECT_CALLABLE_DECLARE(f)
 #define INDIRECT_CALLABLE_SCOPE		static
+#define EXPORT_INDIRECT_CALLABLE(f)
 #endif
 
 /*

-- 
2.30.0.365.g02bc693789-goog

This commit fixes the errores reported when building for powerpc:

 ERROR: modpost: "ip6_dst_check" [vmlinux] is a static EXPORT_SYMBOL
 ERROR: modpost: "ipv4_dst_check" [vmlinux] is a static EXPORT_SYMBOL
 ERROR: modpost: "ipv4_mtu" [vmlinux] is a static EXPORT_SYMBOL
 ERROR: modpost: "ip6_mtu" [vmlinux] is a static EXPORT_SYMBOL

Fixes: f67fbeaebdc0 ("net: use indirect call helpers for dst_mtu")
Fixes: bbd807dfbf20 ("net: indirect call helpers for ipv4/ipv6 dst_check functions")
Reported-by: Stephen Rothwell <redacted>
Signed-off-by: Brian Vazquez <redacted>
---
 net/ipv4/route.c | 4 ++--
 net/ipv6/route.c | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 9e6537709794..be31e2446470 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c

@@ -1206,7 +1206,7 @@ INDIRECT_CALLABLE_SCOPE struct dst_entry *ipv4_dst_check(struct dst_entry *dst,
 		return NULL;
 	return dst;
 }
-EXPORT_SYMBOL(ipv4_dst_check);
+EXPORT_INDIRECT_CALLABLE(ipv4_dst_check);
 
 static void ipv4_send_dest_unreach(struct sk_buff *skb)
 {

@@ -1337,7 +1337,7 @@ INDIRECT_CALLABLE_SCOPE unsigned int ipv4_mtu(const struct dst_entry *dst)
 
 	return mtu - lwtunnel_headroom(dst->lwtstate, mtu);
 }
-EXPORT_SYMBOL(ipv4_mtu);
+EXPORT_INDIRECT_CALLABLE(ipv4_mtu);
 
 static void ip_del_fnhe(struct fib_nh_common *nhc, __be32 daddr)
 {

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 8d9e053dc071..0d1784b0d65d 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c

@@ -2644,7 +2644,7 @@ INDIRECT_CALLABLE_SCOPE struct dst_entry *ip6_dst_check(struct dst_entry *dst,
 
 	return dst_ret;
 }
-EXPORT_SYMBOL(ip6_dst_check);
+EXPORT_INDIRECT_CALLABLE(ip6_dst_check);
 
 static struct dst_entry *ip6_negative_advice(struct dst_entry *dst)
 {

@@ -3115,7 +3115,7 @@ INDIRECT_CALLABLE_SCOPE unsigned int ip6_mtu(const struct dst_entry *dst)
 
 	return mtu - lwtunnel_headroom(dst->lwtstate, mtu);
 }
-EXPORT_SYMBOL(ip6_mtu);
+EXPORT_INDIRECT_CALLABLE(ip6_mtu);
 
 /* MTU selection:
  * 1. mtu on route is locked - use it

-- 
2.30.0.365.g02bc693789-goog

Hello:

This series was applied to netdev/net-next.git (refs/heads/master):

On Thu,  4 Feb 2021 18:18:38 +0000 you wrote:

When a static function is annotated with INDIRECT_CALLABLE_SCOPE and
CONFIG_RETPOLINE is set, the static keyword is removed. Sometimes the
function needs to be exported but EXPORT_SYMBOL can't be used because if
CONFIG_RETPOLINE is not set, we will attempt to export a static symbol.

This patch introduces a new indirect call wrapper:
EXPORT_INDIRECT_CALLABLE. This basically does EXPORT_SYMBOL when
CONFIG_RETPOLINE is set, but does nothing when it's not.

[...]

Here is the summary with links:
  - [net-next,1/2] net: add EXPORT_INDIRECT_CALLABLE wrapper
    https://git.kernel.org/netdev/net-next/c/0053859496ba
  - [net-next,2/2] net: fix building errors on powerpc when CONFIG_RETPOLINE is not set
    https://git.kernel.org/netdev/net-next/c/9c97921a51a0

You are awesome, thank you!
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