x86: Handle KCOV __init vs inline mismatches

GCC appears to have kind of fragile inlining heuristics, in the
sense that it can change whether or not it inlines something based on
optimizations. It looks like the kcov instrumentation being added (or in
this case, removed) from a function changes the optimization results,
and some functions marked "inline" are _not_ inlined. In that case,
we end up with __init code calling a function not marked __init, and we
get the build warnings I'm trying to eliminate in the coming patch that
adds __no_sanitize_coverage to __init functions:

WARNING: modpost: vmlinux: section mismatch in reference: xbc_exit+0x8 (section: .text.unlikely) -> _xbc_exit (section: .init.text)
WARNING: modpost: vmlinux: section mismatch in reference: real_mode_size_needed+0x15 (section: .text.unlikely) -> real_mode_blob_end (section: .init.data)
WARNING: modpost: vmlinux: section mismatch in reference: __set_percpu_decrypted+0x16 (section: .text.unlikely) -> early_set_memory_decrypted (section: .init.text)
WARNING: modpost: vmlinux: section mismatch in reference: memblock_alloc_from+0x26 (section: .text.unlikely) -> memblock_alloc_try_nid (section: .init.text)
WARNING: modpost: vmlinux: section mismatch in reference: acpi_arch_set_root_pointer+0xc (section: .text.unlikely) -> x86_init (section: .init.data)
WARNING: modpost: vmlinux: section mismatch in reference: acpi_arch_get_root_pointer+0x8 (section: .text.unlikely) -> x86_init (section: .init.data)
WARNING: modpost: vmlinux: section mismatch in reference: efi_config_table_is_usable+0x16 (section: .text.unlikely) -> xen_efi_config_table_is_usable (section: .init.text)

This problem is somewhat fragile (though using either __always_inline
or __init will deterministically solve it), but we've tripped over
this before with GCC and the solution has usually been to just use
__always_inline and move on.

For x86 this means forcing several functions to be inline with
__always_inline.

Link: https://lore.kernel.org/r/20250724055029.3623499-2-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/smp.h b/include/linux/smp.h
index f1aa0952e8c3..84e948eb1c20 100644
--- a/include/linux/smp.h
+++ b/include/linux/smp.h
@@ -221,7 +221,7 @@ static inline void wake_up_all_idle_cpus(void) {  }
 
 #ifdef CONFIG_UP_LATE_INIT
 extern void __init up_late_init(void);
-static inline void smp_init(void) { up_late_init(); }
+static __always_inline void smp_init(void) { up_late_init(); }
 #else
 static inline void smp_init(void) { }
 #endif