Re: [PATCH v4 2/4] x86: Handle KCOV __init vs inline mismatches

[Mike Rapoport <rppt@kernel.org>]

On Wed, Jul 23, 2025 at 10:50:26PM -0700, Kees Cook wrote:
> 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.
> 
> Signed-off-by: Kees Cook <kees@kernel.org>

For memblock bit:

Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

-- 
Sincerely yours,
Mike.