[tor-bugs] #24794 [Core Tor/Tor]: smartlist.rs: do not use i8 interchangeably with libc::c_char

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#24794: smartlist.rs: do not use i8 interchangeably with libc::c_char
------------------------------+--------------------------------
     Reporter:  nickm         |      Owner:  nickm
         Type:  defect        |     Status:  assigned
     Priority:  Medium        |  Milestone:  Tor: 0.3.3.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  rust
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
------------------------------+--------------------------------
 I tried to look at why our arm rust builds are failing, and found these
 warnings:
 {{{
 20:53:59   --> /srv/jenkins-workspace/workspace/tor-ci-linux-master-rust-
 arm/ARCHITECTURE/armhf/SUITE/sid/tor/src/rust/smartlist/smartlist.rs:37:44
 20:53:59    |
 20:53:59 37 |             unsafe { slice::from_raw_parts(self.list,
 self.num_used as usize) };
 20:53:59    |                                            ^^^^^^^^^
 expected i8, found u8
 20:53:59    |
 20:53:59    = note: expected type `*const *const i8`
 20:53:59               found type `*const *const u8`
 20:53:59
 20:53:59 error[E0308]: mismatched types
 20:53:59   --> /srv/jenkins-workspace/workspace/tor-ci-linux-master-rust-
 arm/ARCHITECTURE/armhf/SUITE/sid/tor/src/rust/smartlist/smartlist.rs:46:52
 20:53:59    |
 20:53:59 46 |             let c_string = unsafe { CStr::from_ptr(*elem) };
 20:53:59    |                                                    ^^^^^
 expected u8, found i8
 20:53:59    |
 20:53:59    = note: expected type `*const u8`
 20:53:59               found type `*const i8`
 20:53:59
 }}}

 They happen because we're declaring Stringlist::list as `c_char`, but
 we're declaring elems as `i8`.  That's fine on platforms where C's `char`
 is signed, but on other platforms, `char` is unsigned, and libc::c_char is
 `u8`.

 I believe we can fix this by changing `i8` to `c_char` on this line:
 {{{
         let elems: &[*const i8] =
             unsafe { slice::from_raw_parts(self.list, self.num_used as
 usize) };
 }}}

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24794>
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