[feat] Enforce semantics for write once memory (wom)#1834
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Signed-off-by: Olivier Bégassat <olivier.begassat.cours@gmail.com>
Signed-off-by: Olivier Bégassat <olivier.begassat.cours@gmail.com>
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Pull request overview
This PR aims to introduce/enforce semantics for write-once memory (WOM) by adding specification docs (RAM/ROM/WOM) and beginning an implementation of memory-related MIR constraints in the ZkC constraints translator, along with a small unit-test fixture.
Changes:
- Added markdown specifications for RAM/ROM/WOM constraint semantics and lookup interactions.
- Refactored memory translation in
pkg/zkc/constraints/translator.goto route ROM/WOM/RAM through a sharedtranslateMemoryCommon()and added initial (partial) constraints. - Added a new unit test fixture and a test entry for it.
Reviewed changes
Copilot reviewed 15 out of 15 changed files in this pull request and generated 13 comments.
Show a summary per file
| File | Description |
|---|---|
| wom.md | New WOM constraint specification (docs) including bus interaction pseudocode and lookup mapping. |
| rom.md | New ROM constraint specification (docs). |
| ram.md | New RAM constraint specification (docs) and discussion of finalization. |
| pkg/zkc/constraints/translator.go | Implements shared memory translation and adds initial flag/timestamp constraints for memories. |
| pkg/ir/mir/constraint.go | Adds placeholder constructors for send/receive constraints. |
| pkg/test/zkc_unit_test.go | Adds a new unit test invoking the new _example fixture. |
| testdata/zkc/unit/_example.zkc | New unit test program fixture. |
| testdata/zkc/unit/_example.accepts | New expected I/O JSON for the _example fixture. |
| testdata/zkc/unit/_example_0.zkc | Additional example fixture (not referenced by the new test entry). |
| pkg/zkc/compiler/parser/environment.go | Receiver renaming cleanup for Environment methods. |
| pkg/zkc/compiler/codegen/statement.go | Comment example formatting tweak (documentation-only). |
| pkg/zkc/compiler/ast/decl/decl.go | Expanded Declaration doc comment. |
| pkg/schema/constraint/vanishing/constraint.go | Comment punctuation tweak. |
| pkg/schema/constraint/ranged/constraint.go | Comment punctuation tweak. |
| pkg/ir/hir/constraint.go | Comment punctuation tweak. |
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| memoryModule.AddRegisters(register.NewComputed("timestamp_read", timestampWidth, padding)) | ||
| memoryModule.AddRegisters(register.NewComputed("timestamp_write", timestampWidth, padding)) | ||
| memoryModule.AddRegisters(register.NewComputed("timestamp_delta", timestampWidth, padding)) |
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| // Write once memory and read only memory are equivalent on the constraints level | ||
| func translateWriteOnceMemory[F field.Element[F]]( | ||
| ctx schema.ModuleId, fm vm.InputOutputMemory[F]) mir.Module[F] { | ||
| var name = trace.ModuleName{Name: fm.Name(), Multiplier: 1} | ||
| return translateMemoryCommon(ctx, fm, name) | ||
| } |
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| func NewSendConstraint[F field.Element[F]](handle string, sources []register.Id) Constraint[F] { | ||
| // TODO | ||
| return Constraint[F]{} | ||
| } |
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| func NewReceiveConstraint[F field.Element[F]](handle string, sources []register.Id) Constraint[F] { | ||
| // TODO | ||
| return Constraint[F]{} | ||
| } |
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| // > var t tmp | ||
| // > tmp = f(...) |
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| // bus interactions | ||
| if WAS_ALREADY_WRITTEN_TO = true then | ||
| // address of ROM was written to at some point | ||
| snd( ADDRESS, 0, VALUE ) // initialization | ||
| rcv( ADDRESS, TIMESTAMP_READ, VALUE ) // finalization |
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| ```rust | ||
| rcv( address, timestamp, is_written, value ) | ||
| snd( address, timestamp, is_written, value ) | ||
| ``` |
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| ### Triggering the finalization phase | ||
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| To avoid ROM, WOM, and RAM all share the same issue wrt the logUpBus: if initialization/finalization isn't tightly constrained a memory cell can end up living many parallel lives. One constraint that removes this issue is to impose that these memory-types perform a single initialiazation/finalization event per address. Here's one way of doing this in our RISCV zkVM/zkc interpreter: |
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| // executed at program end | ||
| if pc == MAX_UINT_64 { | ||
| // finaliztion of ROM's |
| snd( address, timestamp, value ) | ||
| ``` | ||
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| Any zkc module `MOD` that allows one to touch the WOM requires the following columns |
8 tasks
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