analyze: tracking issue for simple_buffer

[spernsteiner]

simple_buffer is a simplified buffer implementation (similar to Vec<u8>) designed to mimic lighttpd's buffer module.

• [x] borrowck panic: Missing origin params on Rvalue::Cast output. This is triggered by malloc(...) as *mut buffer. buffer has one origin param for its internal data pointer, but the borrowck::LTy computed for the cast has no origin params.
• [ ] unlower panic: Missing entry for Rvalue::Ref arising from let ref mut fresh = ...;.
• [x] borrowck: return malloc(...) removes UNIQUE from the output pointer because Polonius reports an error.
• [ ] borrowck: Drops UNIQUE due to overlapping borrows around realloc:

  buf->data = realloc(buf->data, ...);

  let fresh = &mut (*buf).data;
  *fresh = realloc((*buf).data, ...);

  • Even ignoring the Polonius error, this results in a rustc borrowck error after rewriting
• [ ] borrowck: Drops UNIQUE due to two-phase-like behavior in buffer_realloc(buf, (*buf).cap * 2).
  • [ ] Check whether lighttpd buffer actually uses this pattern
• [x] mir_op: Investigate malloc/realloc calls not being recognized as rewritable via SafeMalloc/SafeRealloc.
  • Caused by missing pointee and missing zero-init support
• [ ] derive(Copy) is left on struct buffer even after rewriting the data pointer to use Box.
• [x] rewrite: Many bad interactions between Option (NULL) and Result (DynOwned/FREE) rewrites.
  • [x] Develop test cases for individual issues
• [x] pointee: Missing pointee type for data due to lack of interprocedural inference variable handling. The pointee analysis creates an inference variable for each malloc call; currently, this must be unified with a concrete type (e.g. u8) within the current function, or else the result will be marked incomplete.
• [x] mir_op: Zero-initializing pointers is currently unsupported.

[spernsteiner]

We can now analyze, rewrite, compile, and run simple_buffer after patching it with workarounds for various c2rust-analyze issues. As we fix the issues tracked here, we can remove the workarounds until simple_buffer works unmodified.

[spernsteiner]

I've implemented fully interprocedural pointee type analysis (on a dev branch - no PR yet), and it now produces correct pointee types for the data field and for all malloc/free/realloc calls. Next I'm planning to look at the borrowck Rvalue::Cast issue.