Fix usage of live in opcodes and no longer preserve registers by default

Many opcodes have a live parameter which is the number of registers that should be preserved by GC operations. Take this into account and conversely stop preserving registers by default. This affects significantly the safety of `memory_ensure_free` when writing nifs. Indeed, arguments (which come from registers) are no longer preserved. However, no platform-specific nif was found that needed to be fixed. If required, calls to `memory_ensure_free` or `memory_ensure_free_opt` should be replaced with calls to `memory_ensure_free_with_roots`. Signed-off-by: Paul Guyot <[email protected]>
pguyot · Oct 16, 2023 · 73eda50 · 73eda50
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Fixed a bug where guards would raise exceptions instead of just being false
+- Fixed interpretation of live for opcodes, thus altering GC semantics for nifs. See also [UPDATING](UPDATING.md).
 
 ## [0.6.0-alpha.1] - 2023-10-09
 

diff --git a/UPDATING.md b/UPDATING.md
@@ -6,6 +6,13 @@
 
 # AtomVM Update Instructions
 
+## v0.6.0-alpha.1 -> v0.6.0-alpha.2
+
+- Registers are no longer preserved by GC by default when invoking nifs, as part of the fix
+of interpretation of the emulator of the live parameter of many opcodes. NIFs may need
+to call `memory_ensure_free_with_roots` and pass their arguments are roots, instead of
+`memory_ensure_free` or `memory_ensure_free_opt`.
+
 ## v0.6.0-alpha.0 -> v0.6.0-alpha.1
 
 - **Libraries (or boot .avm file) from latest version must be used**. Standard library from