Re: [linux-next:master 13069/13300] error[E0425]: cannot find value `VM_MERGEABLE` in crate `bindings`

[John Hubbard <jhubbard@nvidia.com>]

On 10/2/25 2:42 PM, Miguel Ojeda wrote:
> On Thu, Oct 2, 2025 at 11:19 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>>
>> No idea.  Let me cc rust-for-linux.
>>
>> It's a one-line patch:
>>
>> --- a/include/linux/mm.h~mm-ksm-fix-flag-dropping-behavior-in-ksm_madvise
>> +++ a/include/linux/mm.h
>> @@ -296,7 +296,7 @@ extern unsigned int kobjsize(const void
>>  #define VM_MIXEDMAP    0x10000000      /* Can contain "struct page" and pure PFN pages */
>>  #define VM_HUGEPAGE    0x20000000      /* MADV_HUGEPAGE marked this vma */
>>  #define VM_NOHUGEPAGE  0x40000000      /* MADV_NOHUGEPAGE marked this vma */
>> -#define VM_MERGEABLE   0x80000000      /* KSM may merge identical pages */
>> +#define VM_MERGEABLE   BIT(31)         /* KSM may merge identical pages */
>>
>>  #ifdef CONFIG_ARCH_USES_HIGH_VMA_FLAGS
>>  #define VM_HIGH_ARCH_BIT_0     32      /* bit only usable on 64-bit architectures */
> 
> Yeah, non-trivial macros confuse `bindgen`.
> 
> For the moment, you can do e.g. [1].
> 
> Other times, we have changed `#define`s into `enum`s -- that also works.

It seems like bindgen's --clang-macro-fallback argument can avoid the
entire class of problems, is there some reason Rust for Linux has avoided
that option?

Although, in order to make it work with fixdep, additional somewhat complex
build system changes are required. I've got it to almost work locally just
now... :)

thanks,
John Hubbard

> 
> I hope that helps.
> 
> Cheers,
> Miguel
> 
> [1]
> 
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index 5128e2f12038..918f4c74067b 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -106,3 +106,5 @@ const xa_mark_t RUST_CONST_HELPER_XA_PRESENT = XA_PRESENT;
> 
>  const gfp_t RUST_CONST_HELPER_XA_FLAGS_ALLOC = XA_FLAGS_ALLOC;
>  const gfp_t RUST_CONST_HELPER_XA_FLAGS_ALLOC1 = XA_FLAGS_ALLOC1;
> +
> +const vm_flags_t RUST_CONST_HELPER_VM_MERGEABLE = VM_MERGEABLE;
>