Fix some compiled errors(mismatched types)

[poppycompass]

Building the hello-world module according to README.md results in errors.

Environment

generic/ubuntu1810 box in Vagrant with Virtualbox

vagrant@ubuntu1810/: uname -a
Linux ubuntu1810.localdomain 4.18.0-25-generic #26-Ubuntu SMP Mon Jun 24 09:32:08 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

vagrant@ubuntu1810:/$ clang -v
clang version 7.0.0-3 (tags/RELEASE_700/final)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/8
Candidate multilib: .;@m64
Selected multilib: .;@m64
 
vagrant@ubuntu1810:/$ rustup -v
rustup 1.21.1 (7832b2ebe 2019-12-20)

error messages

$ cd linux-kernel-module-rust/hello-world
$ make
...(snip)...
error[E0308]: mismatched types
  --> /vagrant_data/linux-kernel-module-rust/src/allocator.rs:13:41
   |
13 |         bindings::krealloc(ptr::null(), layout.size(), bindings::GFP_KERNEL) as *mut u8
   |                                         ^^^^^^^^^^^^^ expected `u64`, found `usize`
   |
help: you can convert an `usize` to `u64` and panic if the converted value wouldn't fit
   |
13 |         bindings::krealloc(ptr::null(), layout.size().try_into().unwrap(), bindings::GFP_KERNEL) as *mut u8
   |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0308]: mismatched types
   --> /vagrant_data/linux-kernel-module-rust/src/file_operations.rs:193:28
    |
193 |         self.0.read = Some(read_callback::<T>);
    |                            ^^^^^^^^^^^^^^^^^^ expected `u64`, found `usize`
    |
    = note: expected fn pointer `unsafe extern "C" fn(_, _, u64, _) -> i64`
                  found fn item `unsafe extern "C" fn(_, _, usize, _) -> isize {file_operations::read_callback::<T>}`

error[E0308]: mismatched types
   --> /vagrant_data/linux-kernel-module-rust/src/file_operations.rs:200:29
    |
200 |         self.0.write = Some(write_callback::<T>);
    |                             ^^^^^^^^^^^^^^^^^^^ expected `u64`, found `usize`
    |
    = note: expected fn pointer `unsafe extern "C" fn(_, _, u64, _) -> i64`
                  found fn item `unsafe extern "C" fn(_, _, usize, _) -> isize {file_operations::write_callback::<T>}`

error[E0308]: mismatched types
   --> /vagrant_data/linux-kernel-module-rust/src/sysctl.rs:136:36
    |
136 |                 proc_handler: Some(proc_handler::<T>),
    |                                    ^^^^^^^^^^^^^^^^^ expected `u64`, found `usize`
    |
    = note: expected fn pointer `unsafe extern "C" fn(_, _, _, *mut u64, _) -> _`
                  found fn item `unsafe extern "C" fn(_, _, _, *mut usize, _) -> _ {sysctl::proc_handler::<T>}`

error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0308`.
The following warnings were emitted during compilation:
error: could not compile `linux-kernel-module`.
...(snip)...

I fixed these errors with type cast and change variable type.

[alex]

Thanks for the PR! I'm a bit surprised this would happen on a 4 series kernel.

[emilio]

This seems more likely to be due to the wildcard dependency on bindgen, which recently made the size_t -> usize conversion opt-in, see rust-lang/rust-bindgen#1671

[poppycompass]

Thank you for your comment!
I changed the bindgen version in Cargo.toml as follow.
[-] bindgen = "*"
[+] bindgen = "0.51.0"
Compile successful.

[vext01]

Hi,

Edit: Though I was commenting on the bindgen repo, sorry :P

I think I'm experiencing something similar.

// Callback for `dl_iterate_phdr(3)`.                                                              
unsafe extern "C" fn collect_objs(                                                                 
    info: *mut p_ffi::dl_phdr_info,                                                                
    _sz: size_t,                                                                                   
    data: *mut c_void,                                                                             
) -> c_int {                                                                                       
    ...                                                                                          
};                                                                                                 
                                                                                                       
...                                   
unsafe { p_ffi::dl_iterate_phdr(Some(collect_objs), ret_void_p) };                                 

error[E0308]: mismatched types
   --> src/lib.rs:299:42
    |
299 |     unsafe { p_ffi::dl_iterate_phdr(Some(collect_objs), ret_void_p) };
    |                                          ^^^^^^^^^^^^ expected `u64`, found `usize`
    |
    = note: expected fn pointer `unsafe extern "C" fn(_, u64, _) -> _`
                  found fn item `unsafe extern "C" fn(_, usize, _) -> _ {objects::collect_objs}`

error: aborting due to previous error

Here's the signature of dl_iterate_phdr():

int dl_iterate_phdr(int (*callback)(struct dl_phdr_info *, size_t, void*), void *data);

The second arg to the callback should be size_t not u64. It will probably work on amd64, but not i386.

This arose when i updated bindgen from version 0.41 to 0.53.

Thanks

[emilio]

See rust-lang/rust-bindgen#1671. You can do size_t_is_usize(true) to roll back to the previous behavior.

[poppycompass]

Thank you for your comments.
Fix this error with little change is add bindgen version in linux-kernel-module-rust/Cargo.toml.
bindgen version: "*" -> "0.51"
How about this idea?

[geofft]

Added size_t_is_usize(true) in #235, thanks for the hint!