[vlc-devel] [RFC Patch v2 1/2] libvlc: Add Rust API for writing modules in rust

[Kartik Ohri]

On Thu, Sep 17, 2020 at 1:16 AM Romain Vimont <rom1v at videolabs.io> wrote:

> On Tue, Sep 15, 2020 at 08:04:09PM +0530, Kartik Ohri wrote:
> > On Tue, Sep 15, 2020 at 1:54 PM Alexandre Janniaux <ajanni at videolabs.io>
> > wrote:
> > > > +    pub fn vlc_stream_vaControl(s: *mut stream_t, query: c_int,
> ...) ->
> > > c_int;
> > >
> > > After checking [1], you probably need the following code instead:
> > >
> > >     extern "C" {
> > >         pub unsafe fn vlc_stream_vaControl(s: *mut stream_t, query:
> c_int,
> > > ap: VaList) -> c_int;
> > >     }
> > >     pub unsafe fn vlc_stream_Control(s: *mut stream_t, query: c_int,
> mut
> > > args: ...) -> c_int {
> > >         vlc_stream_vaControl(s, query, args)
> > >     }
> > >
> > > Otherwise, as far as I understand this document, va_start/va_end might
> not
> > > be called correctly.
>
> I confirm (by calling stream.len() for example):
>
>     ==1868204==ERROR: AddressSanitizer: SEGV on unknown address (pc
> 0x7f6b314acd28 bp 0x7f6b1e058710 sp 0x7f6b1e0585a0 T18)
>     ==1868204==The signal is caused by a READ memory access.
>     ==1868204==Hint: this fault was caused by a dereference of a high
> value address (see register values below).  Dissassemble the provided pc to
> learn which register was used.
>         #0 0x7f6b314acd28 in FileControl ../../modules/access/file.c:328
>         #1 0x7f6b4c5a4c3a in vlc_stream_vaControl
> ../../src/input/stream.c:703
>         #2 0x7f6b4c4fc775 in AStreamControl ../../src/input/access.c:281
>         #3 0x7f6b4c5a4c3a in vlc_stream_vaControl
> ../../src/input/stream.c:703
>         #4 0x7f6b314703a9 in AStreamControl
> ../../modules/stream_filter/cache_read.c:470
>         #5 0x7f6b4c5a4c3a in vlc_stream_vaControl
> ../../src/input/stream.c:703
>         #6 0x7f6b3078b635 in
> vlccore_rs::stream::Stream::len::h283ec41cb769dee5
> (/home/rom/projects/vlc-rust/buildasan/modules/.libs/libcuesheet_plugin.so+0x10635)
>         #7 ...
>
> > > I haven't checked in details though, and it needs the
> > > #![feature(c_variadic)] attribute.
> > >
> > > [1]
> > >
> https://github.com/rust-lang/rfcs/blob/26197104b7bb9a5a35db243d639aee6e46d35d75/text/2137-variadic.md
> > >
> > >
> > You are probably right. In that case, the RFC is not yet stabilized so
> > should we drop this part till then from the patch ?
>
> With this patch to expose the variadic vlc_stream_Control():
> https://mailman.videolan.org/pipermail/vlc-devel/2020-September/137598.html
>
> And calling it from Rust instead of the va_list version, it works:
>
> --------8<-------------------------------------------------------------
> diff --git a/src/vlccore-rs/src/stream.rs b/src/vlccore-rs/src/stream.rs
> index 0725a8fe6e..8d1b8c297e 100644
> --- a/src/vlccore-rs/src/stream.rs
> +++ b/src/vlccore-rs/src/stream.rs
> @@ -71,7 +71,7 @@ impl Stream {
>      pub fn len(&self) -> std::result::Result<u64, Error> {
>          let size: u64 = 0;
>          const STREAM_GET_SIZE: i32 = 6;
> -        let result = unsafe { ffi::vlc_stream_vaControl(self.stream,
> STREAM_GET_SIZE, &size) };
> +        let result = unsafe { ffi::vlc_stream_Control(self.stream,
> STREAM_GET_SIZE, &size) };
>          if result != 0 {
>              return Err(Error::new(
>                  ErrorKind::Other,
> @@ -102,7 +102,7 @@ impl Stream {
>          const STREAM_GET_CONTENT_TYPE: i32 = 0;
>          let result: *mut c_char = null_mut();
>          unsafe {
> -            if ffi::vlc_stream_vaControl(self.stream,
> STREAM_GET_CONTENT_TYPE, result) != 0 {
> +            if ffi::vlc_stream_Control(self.stream,
> STREAM_GET_CONTENT_TYPE, result) != 0 {
>                  return None;
>              } else if result.is_null() {
>                  return None;
> diff --git a/src/vlccore-sys/src/stream.rs b/src/vlccore-sys/src/stream.rs
> index c9e8d5f0b3..331b6c81b6 100644
> --- a/src/vlccore-sys/src/stream.rs
> +++ b/src/vlccore-sys/src/stream.rs
> @@ -16,7 +16,7 @@ extern "C" {
>
>      pub fn vlc_stream_Seek(s: *mut stream_t, offset: u64) -> c_int;
>
> -    pub fn vlc_stream_vaControl(s: *mut stream_t, query: c_int, ...) ->
> c_int;
> +    pub fn vlc_stream_Control(s: *mut stream_t, query: c_int, ...) ->
> c_int;
>
>      pub fn vlc_stream_Delete(s: *mut stream_t);
>
> --------8<-------------------------------------------------------------
>
> I noticed a problem during testing: src/vlccore-rs and src/vlccore-sys
> are not rebuilt when sources are modified. Cargo should probably be
> called everytime to check if it must rebuild things.
>
> Yes, this can be done. I can add a Rust Sources variable in the common.am
makefile. It might also be fixed using a cargo workspace. I have been
exploring how to run rustfmt on all rust crates and execute all rust tests.
The best solution seems to be a cargo workspace. I'll try it out and report
my findings.

> Regards
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