Summary

Shadow v2.3.0 is a minor release that contains many bug fixes as well as a large push to convert more code from C to Rust; ~54% of our code is now written in Rust compared to just 39% in C. We have incorporated many improvements to Shadow's design as we migrate to Rust, making the code easier to understand, better tested, and easier to maintain. We plan to continue our focus on migrating code to Rust in our next release.

Primary user-facing changes since v2.2.0:

• If running Shadow in Docker, you should use
  --tmpfs /dev/shm:rw,nosuid,nodev,exec,size=1024g rather than
  --shm-size=1024g to mount /dev/shm as executable. This fixes errors when
  the managed process maps executable pages. #2400
• Added latency modeling and potential thread-yield to rdtsc emulation, allowing
  managed code to avoid deadlock in busy-loops that use only the rdtsc
  instruction and no syscalls. #2314
• The build now internally uses pkg-config to locate glib, instead of a custom
  cmake module. This is the recommended way of getting the
  appropriate glib compile flags, and works better in non-standard layouts such
  as in a guix environment.
• The setup script now has a --search option, which can be used to add
  additional directories to search for pkg-config files, C headers, and
  libraries. It obsoletes the options --library and --include.
• Fixed a bug causing mmap to fail when called on a file descriptor that was
  opened with O_NOFOLLOW. #2353
• Bare executable names are now resolved by searching shadow's PATH.
  Previously these were interpreted as relative to the current directory. For
  backwards compatibility, Shadow will currently prefer a binary in that location
  if one is found but log a warning. Such cases should be disambiguated by using
  an absolute path or prefixing with ./.
• Fixed order-of-operations bug in CoDel control law that could lead to an
  unexpected packet drop schedule. We think the bug could have caused Shadow to
  slightly more aggressively drop packets that have already been sitting in the
  CoDel queue for longer than 110 milliseconds. Based on the results of some Tor
  network simulations, the bug didn't appear to affect Tor network performance
  enough to lead us to believe that previous Tor simulations are invalid. #2479
• Changed the default scheduler from thread-per-host to thread-per-core,
  which has better performance on most machines.
• Experimental host heartbeat log messages are enabled by default
  (experimental.host_heartbeat_interval defaults to "1 sec"), but the format
  of these messages is not stable.
• Some of Shadow's emulated syscalls and object allocations are counted and
  written to a shadow.data/sim-stats.json file.
• Improved experimental strace logging for brk, mmap, munmap, mremap,
  mprotect, open, and openat syscalls.
• Several small simulation examples were added to an examples/ directory.
• Fixed the file access mode for stdin in the managed process (changed from
  O_WRONLY to O_RDONLY).
• Fixed support for readv and writev syscalls, and added support for
  preadv and pwritev.
• Fixed a rare crash in Shadow's shim while logging. #2459
• Set the ifa_netmask field in getifaddrs() to improve compatibility with
  Node.js applications. #2456
• Shadow no longer depends on its absolute installed location, allowing the
  installation directory to be safely moved. #2391
• Shadow now emulated PR_SET_DUMPABLE, allowing it to work for programs that
  try to disable memory inspection. #2370
• Added new test cases to check Shadow's simulated network performance. These
  new tests help us verify that Shadow's network stack is capable of
  facilitating high-bandwidth transfers when using a single TCP stream or when
  using many streams in parallel, and across networks with various latency and
  bandwidth characteristics. Since we run the tests as part of our CI, it is now
  much more likely that we will notice when we make changes that significantly
  reduces Shadow's simulated network performance. We plan to expand the cases
  that we test in future releases. #2549

New Contributors

• @Congyu-Liu made their first contribution in #2353
• @zyansheep made their first contribution in #2447
• @valdaarhun made their first contribution in #2474

Thanks also to Shadow devs @sporksmith, @stevenengler, and @robgjansen!

Full Changelog

The full changelog can be viewed here: v2.2.0...v2.3.0