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]>
atomvm · Oct 26, 2023 · b623659 · b623659
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fixed support for big endian CPUs (such as some MIPS CPUs).
 - Fixed STM32 not aborting when `AVM_ABORT()` is used
 - Fixed a bug that would leave the STM32 trapped in a loop on hard faults, rather than aborting
+- Fixed interpretation of live for opcodes, thus altering GC semantics for nifs. See also [UPDATING](UPDATING.md).
 
 ### Added
 

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