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References: <20230112103147.382416-1-glider@google.com>
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From:   Marco Elver <elver@google.com>
Date:   Thu, 12 Jan 2023 12:34:37 +0100
Message-ID: <CANpmjNMznQsC6ftzy7MCa7uQVCFv=MFg6JW28QdnGPyzFEZn5A@mail.gmail.com>
Subject: Re: [PATCH] kmsan: silence -Wmissing-prototypes warnings
To:     Alexander Potapenko <glider@google.com>
Cc:     linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
        peterz@infradead.org, mingo@redhat.com, dvyukov@google.com,
        linux-mm@kvack.org, kasan-dev@googlegroups.com,
        kernel test robot <lkp@intel.com>,
        Vlastimil Babka <vbabka@suse.cz>
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On Thu, 12 Jan 2023 at 11:31, Alexander Potapenko <glider@google.com> wrote:
>
> When building the kernel with W=1, the compiler reports numerous
> warnings about the missing prototypes for KMSAN instrumentation hooks.
>
> Because these functions are not supposed to be called explicitly by the
> kernel code (calls to them are emitted by the compiler), they do not
> have to be declared in the headers. Instead, we add forward declarations
> right before the definitions to silence the warnings produced by
> -Wmissing-prototypes.
>
> Reported-by: kernel test robot <lkp@intel.com>
> Link: https://lore.kernel.org/lkml/202301020356.dFruA4I5-lkp@intel.com/T/
> Reported-by: Vlastimil Babka <vbabka@suse.cz>
> Suggested-by: Marco Elver <elver@google.com>
> Signed-off-by: Alexander Potapenko <glider@google.com>

Reviewed-by: Marco Elver <elver@google.com>

> ---
>  mm/kmsan/instrumentation.c | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
>
> diff --git a/mm/kmsan/instrumentation.c b/mm/kmsan/instrumentation.c
> index 770fe02904f36..cf12e9616b243 100644
> --- a/mm/kmsan/instrumentation.c
> +++ b/mm/kmsan/instrumentation.c
> @@ -38,7 +38,15 @@ get_shadow_origin_ptr(void *addr, u64 size, bool store)
>         return ret;
>  }
>
> +/*
> + * KMSAN instrumentation functions follow. They are not declared elsewhere in
> + * the kernel code, so they are preceded by prototypes, to silence
> + * -Wmissing-prototypes warnings.
> + */
> +
>  /* Get shadow and origin pointers for a memory load with non-standard size. */
> +struct shadow_origin_ptr __msan_metadata_ptr_for_load_n(void *addr,
> +                                                       uintptr_t size);
>  struct shadow_origin_ptr __msan_metadata_ptr_for_load_n(void *addr,
>                                                         uintptr_t size)
>  {
> @@ -47,6 +55,8 @@ struct shadow_origin_ptr __msan_metadata_ptr_for_load_n(void *addr,
>  EXPORT_SYMBOL(__msan_metadata_ptr_for_load_n);
>
>  /* Get shadow and origin pointers for a memory store with non-standard size. */
> +struct shadow_origin_ptr __msan_metadata_ptr_for_store_n(void *addr,
> +                                                        uintptr_t size);
>  struct shadow_origin_ptr __msan_metadata_ptr_for_store_n(void *addr,
>                                                          uintptr_t size)
>  {
> @@ -59,12 +69,16 @@ EXPORT_SYMBOL(__msan_metadata_ptr_for_store_n);
>   * with fixed size.
>   */
>  #define DECLARE_METADATA_PTR_GETTER(size)                                  \
> +       struct shadow_origin_ptr __msan_metadata_ptr_for_load_##size(      \
> +               void *addr);                                               \
>         struct shadow_origin_ptr __msan_metadata_ptr_for_load_##size(      \
>                 void *addr)                                                \
>         {                                                                  \
>                 return get_shadow_origin_ptr(addr, size, /*store*/ false); \
>         }                                                                  \
>         EXPORT_SYMBOL(__msan_metadata_ptr_for_load_##size);                \
> +       struct shadow_origin_ptr __msan_metadata_ptr_for_store_##size(     \
> +               void *addr);                                               \
>         struct shadow_origin_ptr __msan_metadata_ptr_for_store_##size(     \
>                 void *addr)                                                \
>         {                                                                  \
> @@ -86,6 +100,7 @@ DECLARE_METADATA_PTR_GETTER(8);
>   * entering or leaving IRQ. We omit the check for kmsan_in_runtime() to ensure
>   * the memory written to in these cases is also marked as initialized.
>   */
> +void __msan_instrument_asm_store(void *addr, uintptr_t size);
>  void __msan_instrument_asm_store(void *addr, uintptr_t size)
>  {
>         unsigned long ua_flags;
> @@ -138,6 +153,7 @@ static inline void set_retval_metadata(u64 shadow, depot_stack_handle_t origin)
>  }
>
>  /* Handle llvm.memmove intrinsic. */
> +void *__msan_memmove(void *dst, const void *src, uintptr_t n);
>  void *__msan_memmove(void *dst, const void *src, uintptr_t n)
>  {
>         depot_stack_handle_t origin;
> @@ -162,6 +178,7 @@ void *__msan_memmove(void *dst, const void *src, uintptr_t n)
>  EXPORT_SYMBOL(__msan_memmove);
>
>  /* Handle llvm.memcpy intrinsic. */
> +void *__msan_memcpy(void *dst, const void *src, uintptr_t n);
>  void *__msan_memcpy(void *dst, const void *src, uintptr_t n)
>  {
>         depot_stack_handle_t origin;
> @@ -188,6 +205,7 @@ void *__msan_memcpy(void *dst, const void *src, uintptr_t n)
>  EXPORT_SYMBOL(__msan_memcpy);
>
>  /* Handle llvm.memset intrinsic. */
> +void *__msan_memset(void *dst, int c, uintptr_t n);
>  void *__msan_memset(void *dst, int c, uintptr_t n)
>  {
>         depot_stack_handle_t origin;
> @@ -217,6 +235,7 @@ EXPORT_SYMBOL(__msan_memset);
>   * uninitialized value to memory. When reporting an error, KMSAN unrolls and
>   * prints the whole chain of stores that preceded the use of this value.
>   */
> +depot_stack_handle_t __msan_chain_origin(depot_stack_handle_t origin);
>  depot_stack_handle_t __msan_chain_origin(depot_stack_handle_t origin)
>  {
>         depot_stack_handle_t ret = 0;
> @@ -237,6 +256,7 @@ depot_stack_handle_t __msan_chain_origin(depot_stack_handle_t origin)
>  EXPORT_SYMBOL(__msan_chain_origin);
>
>  /* Poison a local variable when entering a function. */
> +void __msan_poison_alloca(void *address, uintptr_t size, char *descr);
>  void __msan_poison_alloca(void *address, uintptr_t size, char *descr)
>  {
>         depot_stack_handle_t handle;
> @@ -272,6 +292,7 @@ void __msan_poison_alloca(void *address, uintptr_t size, char *descr)
>  EXPORT_SYMBOL(__msan_poison_alloca);
>
>  /* Unpoison a local variable. */
> +void __msan_unpoison_alloca(void *address, uintptr_t size);
>  void __msan_unpoison_alloca(void *address, uintptr_t size)
>  {
>         if (!kmsan_enabled || kmsan_in_runtime())
> @@ -287,6 +308,7 @@ EXPORT_SYMBOL(__msan_unpoison_alloca);
>   * Report that an uninitialized value with the given origin was used in a way
>   * that constituted undefined behavior.
>   */
> +void __msan_warning(u32 origin);
>  void __msan_warning(u32 origin)
>  {
>         if (!kmsan_enabled || kmsan_in_runtime())
> @@ -303,6 +325,7 @@ EXPORT_SYMBOL(__msan_warning);
>   * At the beginning of an instrumented function, obtain the pointer to
>   * `struct kmsan_context_state` holding the metadata for function parameters.
>   */
> +struct kmsan_context_state *__msan_get_context_state(void);
>  struct kmsan_context_state *__msan_get_context_state(void)
>  {
>         return &kmsan_get_context()->cstate;
> --
> 2.39.0.314.g84b9a713c41-goog
>