[PATCH v3 2/2] net: add noinline __init __no_profile to skb_extensions_init() for GCOV compatibility

[Konstantin Khorenko]

With -fprofile-update=atomic in global CFLAGS_GCOV, GCC still cannot
constant-fold the skb_ext_total_length() loop when it is inlined into a
profiled caller.  The existing __no_profile on skb_ext_total_length()
itself is insufficient because after __always_inline expansion the code
resides in the caller's body, which still carries GCOV instrumentation.

Mark skb_extensions_init() with __no_profile so the BUILD_BUG_ON checks
can be evaluated at compile time.  Also mark it noinline to prevent the
compiler from inlining it into skb_init() (which lacks __no_profile),
which would re-expose the function body to GCOV instrumentation.

Add __init since skb_extensions_init() is only called from __init
skb_init().  Previously it was implicitly inlined into the .init.text
section; with noinline it would otherwise remain in permanent .text,
wasting memory after boot.

Build-tested with both CONFIG_GCOV_PROFILE_ALL=y and
CONFIG_KCOV_INSTRUMENT_ALL=y.

Signed-off-by: Konstantin Khorenko <khorenko@xxxxxxxxxxxxx>
---
 net/core/skbuff.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 59fb4b2bb821..0978f526acf4 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -5153,7 +5153,7 @@ static __always_inline __no_profile unsigned int skb_ext_total_length(void)
 	return l;
 }
 
-static void skb_extensions_init(void)
+static noinline void __init __no_profile skb_extensions_init(void)
 {
 	BUILD_BUG_ON(SKB_EXT_NUM > 8);
 	BUILD_BUG_ON(skb_ext_total_length() > 255);
-- 
2.43.5