feat: enable recursion

- Introduces smoke test with verification of empty program
- Implements `get_random_custom_v03` to avoid panics when accessing
  hashmaps

Author: Oppen

Cargo.lock

@@ -1,5 +1,6 @@
 .PHONY: deps deps-linux deps-macos compile-programs-asm compile-programs-rust compile-bench \
-compile-programs clean-asm clean-rust clean-bench clean-shared clean test test-asm \
+compile-programs compile-recursion-elfs clean-asm clean-rust clean-bench clean-shared \
+clean-recursion-elfs clean test test-asm \
 test-rust test-executor test-flamegraph flamegraph-prover \
 test-fast test-prover test-prover-all test-disk-spill test-math-cuda test-cuda-integration \
 bench-math-cuda bench-prover bench-prover-cuda build check clippy fmt lint regen-ethrex-fixtures \
@@ -46,6 +47,13 @@ BENCH_PROGRAM_DIRS := $(dir $(wildcard $(BENCH_PROGRAMS_DIR)/*/Cargo.toml))
 BENCH_PROGRAMS := $(notdir $(basename $(BENCH_PROGRAM_DIRS:%/=%)))
 BENCH_ARTIFACTS := $(addprefix $(BENCH_ARTIFACTS_DIR)/, $(addsuffix .elf, $(BENCH_PROGRAMS)))
 
+# Recursion smoke-test guests, in bench_vs/lambda/ (shared with bench_vs/run.sh)
+# rather than executor/programs/. The recursion guest is the in-VM STARK verifier.
+RECURSION_GUESTS_DIR=./bench_vs/lambda
+RECURSION_ARTIFACTS_DIR=./executor/program_artifacts/recursion
+RECURSION_GUESTS := empty fibonacci recursion
+RECURSION_ARTIFACTS := $(addprefix $(RECURSION_ARTIFACTS_DIR)/, $(addsuffix .elf, $(RECURSION_GUESTS)))
+
 # Override with: make ... SYSROOT_DIR=$HOME/.lambda-vm-sysroot
 # to install the sysroot in a user-writable location and avoid sudo.
 SYSROOT_DIR ?= /opt/lambda-vm-sysroot
@@ -133,7 +141,12 @@ compile-programs-rust: prepare-sysroot $(RUST_ARTIFACTS)
 
 compile-bench: prepare-sysroot $(BENCH_ARTIFACTS)
 
-compile-programs: compile-programs-asm compile-programs-rust compile-bench
+compile-programs: compile-programs-asm compile-programs-rust compile-bench compile-recursion-elfs
+
+compile-recursion-elfs: prepare-sysroot $(RECURSION_ARTIFACTS)
+
+$(RECURSION_ARTIFACTS_DIR):
+	mkdir -p $@
 
 
 $(RUST_ARTIFACTS_DIR):
@@ -142,13 +155,19 @@ $(RUST_ARTIFACTS_DIR):
 $(BENCH_ARTIFACTS_DIR):
 	mkdir -p $@
 
+# The guest .elf rules depend on FORCE so their recipe always runs: cargo already
+# tracks the full dependency graph, so we let it decide what to rebuild (a fast
+# no-op when nothing changed) rather than re-encode that in Make prereqs.
+.PHONY: FORCE
+FORCE:
+
 # Compile rust (64-bit)
 # Order-only `| prepare-sysroot` so a direct `make .../foo.elf` provisions the sysroot
 # first (the aggregate compile-programs-rust/compile-bench targets already do, but a
 # bare pattern-rule invocation like `make -B .../ethrex.elf` would otherwise skip it
 # and fail to compile guest C dependencies). Order-only because prepare-sysroot is
 # .PHONY — a normal prereq would force a rebuild every time; its recipe is idempotent.
-$(RUST_ARTIFACTS_DIR)/%.elf: $(RUST_PROGRAMS_DIR)/%/Cargo.toml | prepare-sysroot $(RUST_ARTIFACTS_DIR)
+$(RUST_ARTIFACTS_DIR)/%.elf: FORCE | prepare-sysroot $(RUST_ARTIFACTS_DIR)
 	cd $(RUST_PROGRAMS_DIR)/$* && \
 		CARGO_TARGET_DIR=$(abspath $(SHARED_TARGET_DIR)) \
 		CFLAGS_riscv64im_lambda_vm_elf="$(SYSROOT_CFLAGS)" \
@@ -160,7 +179,7 @@ $(RUST_ARTIFACTS_DIR)/%.elf: $(RUST_PROGRAMS_DIR)/%/Cargo.toml | prepare-sysroot
 	cp $(SHARED_TARGET_DIR)/riscv64im-lambda-vm-elf/release/$* $@
 
 # Compile rust benches (64-bit)
-$(BENCH_ARTIFACTS_DIR)/%.elf: $(BENCH_PROGRAMS_DIR)/%/Cargo.toml | prepare-sysroot $(BENCH_ARTIFACTS_DIR)
+$(BENCH_ARTIFACTS_DIR)/%.elf: FORCE | prepare-sysroot $(BENCH_ARTIFACTS_DIR)
 	cd $(BENCH_PROGRAMS_DIR)/$* && \
 		CARGO_TARGET_DIR=$(abspath $(SHARED_TARGET_DIR)) \
 		CFLAGS_riscv64im_lambda_vm_elf="$(SYSROOT_CFLAGS)" \
@@ -171,6 +190,22 @@ $(BENCH_ARTIFACTS_DIR)/%.elf: $(BENCH_PROGRAMS_DIR)/%/Cargo.toml | prepare-sysro
 			-Z json-target-spec
 	cp $(SHARED_TARGET_DIR)/riscv64im-lambda-vm-elf/release/$* $@
 
+# Recursion-suite guests: same standard guest flags as compile-bench (std-inclusive
+# build-std works for both the no_std inner guests and the std recursion verifier).
+# The crate's binary is <name>-bench; copy it to <name>.elf so prover tests read
+# prebuilt artifacts like every other program (see
+# prover/src/tests/recursion_smoke_test.rs), instead of shelling out.
+$(RECURSION_ARTIFACTS_DIR)/%.elf: FORCE | prepare-sysroot $(RECURSION_ARTIFACTS_DIR)
+	cd $(RECURSION_GUESTS_DIR)/$* && \
+		CARGO_TARGET_DIR=$(abspath $(SHARED_TARGET_DIR)) \
+		CFLAGS_riscv64im_lambda_vm_elf="$(SYSROOT_CFLAGS)" \
+		rustup run nightly-2026-02-01 cargo build --release \
+			--target $(RV64_TARGET_SPEC) \
+			-Z build-std=core,alloc,std,compiler_builtins,panic_abort \
+			-Z build-std-features=compiler-builtins-mem \
+			-Z json-target-spec
+	cp $(SHARED_TARGET_DIR)/riscv64im-lambda-vm-elf/release/$*-bench $@
+
 clean-asm:
 	-rm -rf $(ASM_ARTIFACTS_DIR)
 
@@ -183,7 +218,10 @@ clean-bench:
 clean-shared:
 	-rm -rf $(SHARED_TARGET_DIR)
 
-clean: clean-asm clean-rust clean-bench clean-shared
+clean-recursion-elfs:
+	-rm -rf $(RECURSION_ARTIFACTS_DIR)
+
+clean: clean-asm clean-rust clean-bench clean-shared clean-recursion-elfs
 
 test-executor: compile-programs
 	cargo test -p executor
@@ -225,8 +263,9 @@ test-fast:
 test-prover:
 	cargo test -p lambda-vm-prover
 
-# Prover tests including slow ones
-test-prover-all:
+# Prover tests including slow ones. The recursion smoke tests (#[ignore]d) read
+# prebuilt guest ELFs from executor/program_artifacts/recursion/, so build them first.
+test-prover-all: compile-recursion-elfs
 	cargo test -p lambda-vm-prover -- --include-ignored
 
 # Prover tests with debug-checks (shows bus balance report)

Makefile

@@ -0,0 +1,6 @@
+[target.riscv64im-lambda-vm-elf]
+rustflags = [
+  "-C", "link-arg=-e",
+  "-C", "link-arg=main",
+  "-C", "passes=lower-atomic"
+]

bench_vs/lambda/empty/.cargo/config.toml

@@ -0,0 +1,8 @@
+[workspace]
+
+[package]
+name = "empty-bench"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

bench_vs/lambda/empty/Cargo.lock

@@ -0,0 +1,28 @@
+#![no_std]
+#![no_main]
+
+use core::arch::asm;
+use core::panic::PanicInfo;
+
+const SYSCALL_HALT: u64 = 93;
+
+#[panic_handler]
+fn panic(_info: &PanicInfo) -> ! {
+    loop {}
+}
+
+fn halt() -> ! {
+    unsafe {
+        asm!(
+            "ecall",
+            in("a0") 0u64,
+            in("a7") SYSCALL_HALT,
+            options(noreturn),
+        );
+    }
+}
+
+#[unsafe(no_mangle)]
+pub fn main() -> ! {
+    halt()
+}

bench_vs/lambda/empty/Cargo.toml

@@ -0,0 +1,7 @@
+[target.riscv64im-lambda-vm-elf]
+rustflags = [
+  "-C", "link-arg=-e",
+  "-C", "link-arg=main",
+  "--cfg", "getrandom_backend=\"custom\"",
+  "-C", "passes=lower-atomic"
+]