fix: memory leak (#48)

* Fix memory leak

* Add destructor patch

* Avoid double free

.github/actions/compile-witness-generator/action.yml

@@ -104,6 +104,16 @@ runs:
         if [ "$OS" = "macos" ]; then SED_I="sed -i ''"; fi
         $SED_I ':a;N;$!ba;s/\n}\n\n*$/\n  return 0;\n}/' "${CIRCUIT_CPP_PATH}/main.cpp"
 
+    # circom's --c backend emits an empty ~Circom_CalcWit destructor (the binary
+    # exits after one witness); linked as a library it leaks the signal buffer on
+    # every call. Patch the destructor to free the per-call allocations.
+    - name: Patch ${{ inputs.circuit-name-display }} CalcWit Leak
+      shell: bash
+      env:
+        WITNESS_GENERATOR_RESOURCES_PATH: ${{ steps.parse-circuit-path.outputs.WITNESS_GENERATOR_RESOURCES_PATH }}
+        CIRCUIT_CPP_PATH: ${{ steps.parse-circuit-path.outputs.CIRCUIT_CPP_PATH }}
+      run: sh "${WITNESS_GENERATOR_RESOURCES_PATH}/fix_calcwit_leak.sh" "${CIRCUIT_CPP_PATH}"
+
     - name: Install llvm-objcopy (macOS)
       if: ${{ inputs.os == 'macos' }}
       shell: bash

.github/resources/witness-generator/fix_calcwit_leak.sh

@@ -0,0 +1,50 @@
+#!/bin/sh
+# Patch the circom-generated `Circom_CalcWit` destructor to free the per-call
+# allocations made in its constructor.
+#
+# circom's `--c` backend emits an EMPTY `~Circom_CalcWit()` destructor on
+# purpose: the generated witness-generator *binary* computes a single witness
+# and then exits, so the OS reclaims everything. We link the generated code as
+# an in-process *library* and call it once per proof, so that empty destructor
+# leaks the entire signal buffer (`signalValues`, ~total_signals * sizeof(Fr) =
+# megabytes), plus `componentMemory` (and its per-component sub-buffers) and
+# `inputSignalAssigned`, on EVERY call.
+#
+# This rewrites the destructor to free those allocations. The per-component
+# frees mirror circom's own `release_memory_component` (guarded `if(ptr)
+# delete[]`), so they are safe even if the generated run already released some
+# components.
+#
+# Usage: fix_calcwit_leak.sh <dir-containing-generated-calcwit.cpp>
+set -eu
+
+DIR="${1:?usage: fix_calcwit_leak.sh <generated-cpp-dir>}"
+CALCWIT="$DIR/calcwit.cpp"
+
+[ -f "$CALCWIT" ] || { echo "fix_calcwit_leak: $CALCWIT not found" >&2; exit 1; }
+
+if grep -q "logos: free per-call allocations" "$CALCWIT"; then
+    echo "fix_calcwit_leak: $CALCWIT already patched, skipping"
+    exit 0
+fi
+
+perl -0777 -i -pe '
+    my $body = q{Circom_CalcWit::~Circom_CalcWit() {
+  // logos: free per-call allocations. circom leaves this destructor empty
+  // because the generated binary exits after one witness; we call the
+  // generated code in-process as a library, so without these frees every
+  // witness-generation call leaks signalValues (megabytes), componentMemory
+  // and inputSignalAssigned. These three are allocated once in the constructor
+  // and freed nowhere else. NOTE: the per-component sub-buffers
+  // (subcomponents/outputIsSet/mutexes/...) are already released during the
+  // witness computation by circoms own release_memory_component, so they must
+  // NOT be freed here -- doing so double-frees.
+  delete[] signalValues;
+  delete[] inputSignalAssigned;
+  delete[] componentMemory;
+}};
+    my $n = (s/Circom_CalcWit::~Circom_CalcWit\s*\(\s*\)\s*\{.*?\n\}/$body/s);
+    die "fix_calcwit_leak: could not locate ~Circom_CalcWit() destructor\n" unless $n == 1;
+' "$CALCWIT"
+
+echo "fix_calcwit_leak: patched $CALCWIT"

justfile

@@ -1,6 +1,7 @@
 cargo_root      := justfile_directory() + "/rust"
 src             := justfile_directory() + "/src"
 ci_makefile     := justfile_directory() + "/.github/resources/witness-generator/Makefile"
+calcwit_fix     := justfile_directory() + "/.github/resources/witness-generator/fix_calcwit_leak.sh"
 circom_version  := "2.2.2" # This version must match the version used in the CI
 
 os := `uname -s`
@@ -34,6 +35,8 @@ poq: check-circom
     circom blend/poq.circom --c --r1cs --no_asm --O2 --output blend
     # circom-generated main() has no return on the success path; patch it before -O3 turns it into an infinite loop
     {{sed_i}} ':a;N;$!ba;s/\n}\n\n*$/\n  return 0;\n}/' blend/poq_cpp/main.cpp
+    # circom's empty ~Circom_CalcWit destructor leaks per call when linked as a library; free the per-call allocations
+    sh {{calcwit_fix}} blend/poq_cpp
     cp -r {{src}}/poq blend/poq_cpp/poq
     cp {{src}}/circom_adapter.cpp {{src}}/circom_adapter.hpp {{src}}/circom_fwd.hpp {{src}}/types.hpp {{src}}/assert.h blend/poq_cpp/
     cp {{ci_makefile}} blend/poq_cpp/Makefile
@@ -50,6 +53,8 @@ pol: check-circom
     circom mantle/pol.circom --c --r1cs --no_asm --O2 --output mantle
     # circom-generated main() has no return on the success path; patch it before -O3 turns it into an infinite loop
     {{sed_i}} ':a;N;$!ba;s/\n}\n\n*$/\n  return 0;\n}/' mantle/pol_cpp/main.cpp
+    # circom's empty ~Circom_CalcWit destructor leaks per call when linked as a library; free the per-call allocations
+    sh {{calcwit_fix}} mantle/pol_cpp
     cp -r {{src}}/pol mantle/pol_cpp/pol
     cp {{src}}/circom_adapter.cpp {{src}}/circom_adapter.hpp {{src}}/circom_fwd.hpp {{src}}/types.hpp {{src}}/assert.h mantle/pol_cpp/
     cp {{ci_makefile}} mantle/pol_cpp/Makefile
@@ -66,6 +71,8 @@ poc: check-circom
     circom mantle/poc.circom --c --r1cs --no_asm --O2 --output mantle
     # circom-generated main() has no return on the success path; patch it before -O3 turns it into an infinite loop
     {{sed_i}} ':a;N;$!ba;s/\n}\n\n*$/\n  return 0;\n}/' mantle/poc_cpp/main.cpp
+    # circom's empty ~Circom_CalcWit destructor leaks per call when linked as a library; free the per-call allocations
+    sh {{calcwit_fix}} mantle/poc_cpp
     cp -r {{src}}/poc mantle/poc_cpp/poc
     cp {{src}}/circom_adapter.cpp {{src}}/circom_adapter.hpp {{src}}/circom_fwd.hpp {{src}}/types.hpp {{src}}/assert.h mantle/poc_cpp/
     cp {{ci_makefile}} mantle/poc_cpp/Makefile
@@ -82,6 +89,8 @@ signature: check-circom
     circom mantle/signature.circom --c --r1cs --no_asm --O2 --output mantle
     # circom-generated main() has no return on the success path; patch it before -O3 turns it into an infinite loop
     {{sed_i}} ':a;N;$!ba;s/\n}\n\n*$/\n  return 0;\n}/' mantle/signature_cpp/main.cpp
+    # circom's empty ~Circom_CalcWit destructor leaks per call when linked as a library; free the per-call allocations
+    sh {{calcwit_fix}} mantle/signature_cpp
     cp -r {{src}}/signature mantle/signature_cpp/signature
     cp {{src}}/circom_adapter.cpp {{src}}/circom_adapter.hpp {{src}}/circom_fwd.hpp {{src}}/types.hpp {{src}}/assert.h mantle/signature_cpp/
     cp {{ci_makefile}} mantle/signature_cpp/Makefile

src/circom_adapter.cpp

@@ -4,6 +4,17 @@
 #include <vector>
 #include <sstream>
 #include <stdexcept>
+#include <mutex>
+
+Circom_Circuit* getCachedCircuit(const ConstBytes& circuit_bytes) {
+    // The circuit is immutable, compiled-in data and has no destructor that
+    // frees its internal buffers, so load it once and keep it for the process
+    // lifetime instead of allocating (and leaking) it on every call.
+    static Circom_Circuit* cached = nullptr;
+    static std::once_flag once;
+    std::call_once(once, [&]() { cached = loadCircuit(circuit_bytes); });
+    return cached;
+}
 
 Circom_Circuit* loadCircuit(const ConstBytes& circuit_bytes) {
     Circom_Circuit* circuit = new Circom_Circuit;

src/circom_adapter.hpp

@@ -7,6 +7,16 @@
 
 // Return value
 Circom_Circuit* loadCircuit(const ConstBytes& circuit);
+
+// Returns a process-wide, lazily-loaded circuit for this library.
+//
+// `loadCircuit` allocates the circuit's internal buffers (input hash map,
+// witness->signal list, constants, IO field defs) but `Circom_Circuit` has no
+// destructor, so `delete circuit` leaks all of them. The circuit is immutable
+// data derived from the compiled-in `.dat`, so we load it exactly once and
+// reuse it for every (including concurrent) witness-generation call.
+Circom_Circuit* getCachedCircuit(const ConstBytes& circuit);
+
 void loadJson(Circom_CalcWit *ctx, const char* inputs_json);
 void writeBinWitness(Circom_CalcWit *ctx, Bytes* output_witness);
 

src/poc/ffi.cpp

@@ -89,26 +89,23 @@ static Status validate_witness_arguments(const WitnessInput* input, const Bytes*
 static Status generate_witness_impl(const WitnessInput* input, Bytes* output) {
     const ConstBytes& circuit_bytes = input->dat;
 
-    Circom_Circuit* circuit = loadCircuit(circuit_bytes);
+    Circom_Circuit* circuit = getCachedCircuit(circuit_bytes);
     Circom_CalcWit* ctx = new Circom_CalcWit(circuit);
 
     try {
         loadJson(ctx, input->inputs_json);
     } catch (...) {
         delete ctx;
-        delete circuit;
         throw;
     }
     if (ctx->getRemaingInputsToBeSet()!=0) {
         const std::string message = "Not all inputs have been set. Only " + std::to_string(get_main_input_signal_no()-ctx->getRemaingInputsToBeSet()) + " out of " + std::to_string(get_main_input_signal_no()) + ".";
         delete ctx;
-        delete circuit;
         return status_new(StatusCode_InvalidInput, message.c_str());
     }
 
     writeBinWitness(ctx, output);
     delete ctx;
-    delete circuit;
 
     return status_ok();
 }

src/pol/ffi.cpp

@@ -89,26 +89,23 @@ static Status validate_witness_arguments(const WitnessInput* input, const Bytes*
 static Status generate_witness_impl(const WitnessInput* input, Bytes* output) {
     const ConstBytes& circuit_bytes = input->dat;
 
-    Circom_Circuit* circuit = loadCircuit(circuit_bytes);
+    Circom_Circuit* circuit = getCachedCircuit(circuit_bytes);
     Circom_CalcWit* ctx = new Circom_CalcWit(circuit);
 
     try {
         loadJson(ctx, input->inputs_json);
     } catch (...) {
         delete ctx;
-        delete circuit;
         throw;
     }
     if (ctx->getRemaingInputsToBeSet()!=0) {
         const std::string message = "Not all inputs have been set. Only " + std::to_string(get_main_input_signal_no()-ctx->getRemaingInputsToBeSet()) + " out of " + std::to_string(get_main_input_signal_no()) + ".";
         delete ctx;
-        delete circuit;
         return status_new(StatusCode_InvalidInput, message.c_str());
     }
 
     writeBinWitness(ctx, output);
     delete ctx;
-    delete circuit;
 
     return status_ok();
 }

src/poq/ffi.cpp

@@ -89,26 +89,23 @@ static Status validate_witness_arguments(const WitnessInput* input, const Bytes*
 static Status generate_witness_impl(const WitnessInput* input, Bytes* output) {
     const ConstBytes& circuit_bytes = input->dat;
 
-    Circom_Circuit* circuit = loadCircuit(circuit_bytes);
+    Circom_Circuit* circuit = getCachedCircuit(circuit_bytes);
     Circom_CalcWit* ctx = new Circom_CalcWit(circuit);
 
     try {
         loadJson(ctx, input->inputs_json);
     } catch (...) {
         delete ctx;
-        delete circuit;
         throw;
     }
     if (ctx->getRemaingInputsToBeSet()!=0) {
         const std::string message = "Not all inputs have been set. Only " + std::to_string(get_main_input_signal_no()-ctx->getRemaingInputsToBeSet()) + " out of " + std::to_string(get_main_input_signal_no()) + ".";
         delete ctx;
-        delete circuit;
         return status_new(StatusCode_InvalidInput, message.c_str());
     }
 
     writeBinWitness(ctx, output);
     delete ctx;
-    delete circuit;
 
     return status_ok();
 }

src/signature/ffi.cpp

@@ -89,26 +89,23 @@ static Status validate_witness_arguments(const WitnessInput* input, const Bytes*
 static Status generate_witness_impl(const WitnessInput* input, Bytes* output) {
     const ConstBytes& circuit_bytes = input->dat;
 
-    Circom_Circuit* circuit = loadCircuit(circuit_bytes);
+    Circom_Circuit* circuit = getCachedCircuit(circuit_bytes);
     Circom_CalcWit* ctx = new Circom_CalcWit(circuit);
 
     try {
         loadJson(ctx, input->inputs_json);
     } catch (...) {
         delete ctx;
-        delete circuit;
         throw;
     }
     if (ctx->getRemaingInputsToBeSet()!=0) {
         const std::string message = "Not all inputs have been set. Only " + std::to_string(get_main_input_signal_no()-ctx->getRemaingInputsToBeSet()) + " out of " + std::to_string(get_main_input_signal_no()) + ".";
         delete ctx;
-        delete circuit;
         return status_new(StatusCode_InvalidInput, message.c_str());
     }
 
     writeBinWitness(ctx, output);
     delete ctx;
-    delete circuit;
 
     return status_ok();
 }