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

[Alice Ryhl <aliceryhl@google.com>]

On Fri, Oct 3, 2025 at 12:28 AM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Thu, 2 Oct 2025 23:42:59 +0200 Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> 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.
> >
> > ...
> >
> > --- 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;
>
> Sorry, this is rather annoying.  Rust is breaking the build for a very
> simple patch.  Many developers aren't rust-enabled and probably aren't
> even able to test a fix - my attempt to get a rust build setup working
> didn't end happily.
>
> Jakub's patch fixes a kernel crash and needs to be merged into mainline
> and -stable reasonably soon.  But that is now blocked until someone who
> knows how to fix this error and how to test it gets down and does those
> things.
>
> Jakub's patch is present in current linux-next.  Can someone please
> send us a fix?

I don't have my git-send-mail-capable laptop with me right now, but
the diff Miguel shared that adds one line to
rust/bindings/bindings_helper.h will fix this build error.

Alice