When CONFIG_GCOV_PROFILE_ALL=y is enabled, the kernel fails to build: In file included from : In function 'skb_extensions_init', inlined from 'skb_init' at net/core/skbuff.c:5214:2: ././include/linux/compiler_types.h:706:45: error: call to '__compiletime_assert_1490' declared with attribute error: BUILD_BUG_ON failed: skb_ext_total_length() > 255 CONFIG_GCOV_PROFILE_ALL adds -fprofile-arcs -ftest-coverage -fno-tree-loop-im to CFLAGS globally. GCC inserts branch profiling counters into the skb_ext_total_length() loop and, combined with -fno-tree-loop-im (which disables loop invariant motion), cannot constant-fold the result. BUILD_BUG_ON requires a compile-time constant and fails. The issue manifests in kernels with 5+ SKB extension types enabled (e.g., after addition of SKB_EXT_CAN, SKB_EXT_PSP). With 4 extensions GCC can still unroll and fold the loop despite GCOV instrumentation; with 5+ it gives up. Mark skb_ext_total_length() with __no_profile to prevent GCOV from inserting counters into this function. Without counters the loop is "clean" and GCC can constant-fold it even with -fno-tree-loop-im active. This allows BUILD_BUG_ON to work correctly while keeping GCOV profiling for the rest of the kernel. This also removes the CONFIG_KCOV_INSTRUMENT_ALL preprocessor guard introduced by d6e5794b06c0, as __no_profile handles both GCOV and KCOV instrumentation at the root cause level rather than just disabling the check. Fixes: 5d21d0a65b57 ("net: generalize calculation of skb extensions length") Fixes: d6e5794b06c0 ("net: avoid build bug in skb extension length calculation") Signed-off-by: Konstantin Khorenko Reviewed-by: Thomas Weißschuh --- net/core/skbuff.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 0e217041958a..47c7f0ab6e84 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -5145,7 +5145,7 @@ static const u8 skb_ext_type_len[] = { #endif }; -static __always_inline unsigned int skb_ext_total_length(void) +static __always_inline __no_profile unsigned int skb_ext_total_length(void) { unsigned int l = SKB_EXT_CHUNKSIZEOF(struct skb_ext); int i; @@ -5159,9 +5159,7 @@ static __always_inline unsigned int skb_ext_total_length(void) static void skb_extensions_init(void) { BUILD_BUG_ON(SKB_EXT_NUM > 8); -#if !IS_ENABLED(CONFIG_KCOV_INSTRUMENT_ALL) BUILD_BUG_ON(skb_ext_total_length() > 255); -#endif skbuff_ext_cache = kmem_cache_create("skbuff_ext_cache", SKB_EXT_ALIGN_VALUE * skb_ext_total_length(), -- 2.43.5