From bebe6dfda0894b0323167a58dd192fea3e45de71 Mon Sep 17 00:00:00 2001
From: hanez <you@hanez.org>
Date: Fri, 10 Apr 2026 22:04:27 +0200
Subject: [PATCH] Made MAX_FRAMES, MAX_FRAME_LOCALS, MAX_GLOBALS, OUTPUT_SIZE
 and STACK_SIZE configurable during build configuration using cmake defines
 (-D). No code changes. (0.40.5)

---
 cmake/Options.cmake |  7 +++++++
 cmake/Targets.cmake |  7 +++++++
 docs/build.md       | 17 +++++++++++++++++
 src/vm.h            | 14 ++++++++++++++
 4 files changed, 45 insertions(+)

diff --git a/cmake/Options.cmake b/cmake/Options.cmake
index 92a5fb8..8ad1fa5 100644
--- a/cmake/Options.cmake
+++ b/cmake/Options.cmake
@@ -33,3 +33,10 @@ endif()
 
 # Debug option to enable verbose parser/VM logging
 option(FUN_DEBUG "Enable extra debug logging in Fun" OFF)
+
+# VM settings (configurable via -D...)
+set(MAX_FRAMES 128 CACHE STRING "Maximum depth of the call stack (frames)")
+set(MAX_FRAME_LOCALS 64 CACHE STRING "Maximum number of local variables per frame")
+set(MAX_GLOBALS 128 CACHE STRING "Maximum number of global variables")
+set(OUTPUT_SIZE 1024 CACHE STRING "Size of the VM output buffer (number of values)")
+set(STACK_SIZE 1024 CACHE STRING "Size of the VM evaluation stack")
diff --git a/cmake/Targets.cmake b/cmake/Targets.cmake
index 0e98eab..9deaeb2 100644
--- a/cmake/Targets.cmake
+++ b/cmake/Targets.cmake
@@ -25,6 +25,13 @@ endif()
 target_compile_definitions(fun_core PUBLIC FUN_VERSION="${PROJECT_VERSION}")
 target_compile_definitions(fun_core PUBLIC DEFAULT_LIB_DIR="${DEFAULT_LIB_DIR}")
 
+# VM configuration
+target_compile_definitions(fun_core PUBLIC MAX_FRAMES=${MAX_FRAMES})
+target_compile_definitions(fun_core PUBLIC MAX_FRAME_LOCALS=${MAX_FRAME_LOCALS})
+target_compile_definitions(fun_core PUBLIC MAX_GLOBALS=${MAX_GLOBALS})
+target_compile_definitions(fun_core PUBLIC OUTPUT_SIZE=${OUTPUT_SIZE})
+target_compile_definitions(fun_core PUBLIC STACK_SIZE=${STACK_SIZE})
+
 # Apply extension include/link variables discovered in cmake/Extensions
 foreach(var_pair
     PCSC
diff --git a/docs/build.md b/docs/build.md
index 9fb92d6..e7b815b 100644
--- a/docs/build.md
+++ b/docs/build.md
@@ -24,6 +24,17 @@ Fun exposes several options you can toggle at configure time:
 - `FUN_WITH_RUST` (ON/OFF) - Build and link Rust staticlib from `src/rust/`
 - `FUN_WITH_OPENSSL` (ON/OFF) - Enable OpenSSL-backed helpers (MD5/SHA-256/SHA-512/RIPEMD-160)
 
+### VM configuration constants
+You can override internal VM limits at compile time by passing `-D<VAR>=<VALUE>` to CMake:
+
+- `MAX_FRAMES` (default: 128) - Maximum depth of the call stack (frames)
+- `MAX_FRAME_LOCALS` (default: 64) - Maximum number of local variables per frame
+- `MAX_GLOBALS` (default: 128) - Maximum number of global variables
+- `OUTPUT_SIZE` (default: 1024) - Size of the VM output buffer (number of values)
+- `STACK_SIZE` (default: 1024) - Size of the VM evaluation stack (number of `Value` slots)
+
+These are defined as `CACHE` variables, so they will persist in your `CMakeCache.txt`.
+
 When configuring, the build prints a summary like:
 
 ```
@@ -59,6 +70,12 @@ cmake -S . -B build_release -DCMAKE_BUILD_TYPE=Release \
 cmake --build build_release --target build
 ```
 
+### Customizing VM limits
+```
+cmake -S . -B build_custom -DSTACK_SIZE=4096 -DMAX_GLOBALS=512
+cmake --build build_custom --target fun
+```
+
 If `FUN_WITH_RUST` is enabled, ensure `cargo` is available in PATH; the build will invoke it and link the produced static library.
 
 If `FUN_WITH_OPENSSL` is enabled, CMake must detect your system OpenSSL (libcrypto).
diff --git a/src/vm.h b/src/vm.h
index 8b47615..ec652b1 100644
--- a/src/vm.h
+++ b/src/vm.h
@@ -13,11 +13,25 @@
 #include "bytecode.h"
 #include <stddef.h>
 
+#ifndef MAX_FRAMES
 #define MAX_FRAMES 128
+#endif
+
+#ifndef MAX_FRAME_LOCALS
 #define MAX_FRAME_LOCALS 64
+#endif
+
+#ifndef MAX_GLOBALS
 #define MAX_GLOBALS 128
+#endif
+
+#ifndef OUTPUT_SIZE
 #define OUTPUT_SIZE 1024
+#endif
+
+#ifndef STACK_SIZE
 #define STACK_SIZE 1024
+#endif
 
 static const char *opcode_names[] = {
   "NOP", "LOAD_CONST", "LOAD_LOCAL", "STORE_LOCAL",