Several `-Z` flags are relevant for Miri:
-* `-Zmir-opt-level` controls how many MIR optimizations are performed. miri
+* `-Zmiri-seed=<hex>` is a custom `-Z` flag added by Miri. It enables the
+ interpreted program to seed an RNG with system entropy. Miri will keep an RNG
+ on its own that is seeded with the given seed, and use that to generate the
+ "system entropy" that seeds the RNG(s) in the interpreted program.
+ **NOTE**: This entropy is not good enough for cryptographic use! Do not
+ generate secret keys in Miri or perform other kinds of cryptographic
+ operations that rely on proper random numbers.
+* `-Zmiri-disable-validation` disables enforcing the validity invariant, which
+ is enforced by default. This is mostly useful for debugging; it means Miri
+ will miss bugs in your program. However, this can also help to make Miri run
+ faster.
+* `-Zmir-opt-level` controls how many MIR optimizations are performed. Miri
overrides the default to be `0`; be advised that using any higher level can
- make miri miss bugs in your program because they got optimized away.
+ make Miri miss bugs in your program because they got optimized away.
* `-Zalways-encode-mir` makes rustc dump MIR even for completely monomorphic
- functions. This is needed so that miri can execute such functions, so miri
+ functions. This is needed so that Miri can execute such functions, so Miri
sets this flag per default.
-* `-Zmiri-disable-validation` is a custom `-Z` flag added by miri. It disables
- enforcing the validity invariant, which is enforced by default. This is
- mostly useful for debugging; it means miri will miss bugs in your program.
Moreover, Miri recognizes some environment variables: