Merge pull request adafruit#8071 from tannewt/cpx_stack_size

Slim down stack frames

Author: tannewt

py/circuitpy_mpconfig.h

@@ -59,8 +59,8 @@ extern void common_hal_mcu_enable_interrupts(void);
 //
 // default is 128; consider raising to reduce fragmentation.
 #define MICROPY_ALLOC_PARSE_CHUNK_INIT   (16)
-// default is 512.
-#define MICROPY_ALLOC_PATH_MAX           (256)
+// default is 512. Longest path in .py bundle as of June 6th, 2023 is 73 characters.
+#define MICROPY_ALLOC_PATH_MAX           (96)
 #define MICROPY_CAN_OVERRIDE_BUILTINS    (1)
 #define MICROPY_COMP_CONST               (1)
 #define MICROPY_COMP_DOUBLE_TUPLE_ASSIGN (1)

py/runtime.c

@@ -201,7 +201,7 @@ mp_obj_t MICROPY_WRAP_MP_LOAD_GLOBAL(mp_load_global)(qstr qst) {
     return elem->value;
 }
 
-mp_obj_t mp_load_build_class(void) {
+mp_obj_t __attribute__((noinline)) mp_load_build_class(void) {
     DEBUG_OP_printf("load_build_class\n");
     #if MICROPY_CAN_OVERRIDE_BUILTINS
     if (MP_STATE_VM(mp_module_builtins_override_dict) != NULL) {
@@ -858,7 +858,7 @@ mp_obj_t mp_call_method_n_kw_var(bool have_self, size_t n_args_n_kw, const mp_ob
 }
 
 // unpacked items are stored in reverse order into the array pointed to by items
-void mp_unpack_sequence(mp_obj_t seq_in, size_t num, mp_obj_t *items) {
+void __attribute__((noinline,)) mp_unpack_sequence(mp_obj_t seq_in, size_t num, mp_obj_t *items) {
     size_t seq_len;
     if (mp_obj_is_type(seq_in, &mp_type_tuple) || mp_obj_is_type(seq_in, &mp_type_list)) {
         mp_obj_t *seq_items;
@@ -905,7 +905,7 @@ void mp_unpack_sequence(mp_obj_t seq_in, size_t num, mp_obj_t *items) {
 }
 
 // unpacked items are stored in reverse order into the array pointed to by items
-void mp_unpack_ex(mp_obj_t seq_in, size_t num_in, mp_obj_t *items) {
+void __attribute__((noinline)) mp_unpack_ex(mp_obj_t seq_in, size_t num_in, mp_obj_t *items) {
     size_t num_left = num_in & 0xff;
     size_t num_right = (num_in >> 8) & 0xff;
     DEBUG_OP_printf("unpack ex " UINT_FMT " " UINT_FMT "\n", num_left, num_right);
@@ -1482,7 +1482,7 @@ mp_obj_t mp_import_name(qstr name, mp_obj_t fromlist, mp_obj_t level) {
     return mp_builtin___import__(5, args);
 }
 
-mp_obj_t mp_import_from(mp_obj_t module, qstr name) {
+mp_obj_t __attribute__((noinline,)) mp_import_from(mp_obj_t module, qstr name) {
     DEBUG_printf("import from %p %s\n", module, qstr_str(name));
 
     mp_obj_t dest[2];
@@ -1528,7 +1528,7 @@ mp_obj_t mp_import_from(mp_obj_t module, qstr name) {
     #endif
 }
 
-void mp_import_all(mp_obj_t module) {
+void __attribute__((noinline)) mp_import_all(mp_obj_t module) {
     DEBUG_printf("import all %p\n", module);
 
     // TODO: Support __all__

tools/gdb-stack-size.py

@@ -0,0 +1,64 @@
+"""Source this file into gdb `source ../../tools/gdb-stack-size.py` then run
+   `stack-size` to print a backtrace with each frame size next to it."""
+
+
+class StackSize(gdb.Command):
+    def __init__(self):
+        super(StackSize, self).__init__("stack-size", gdb.COMMAND_USER)
+
+    def invoke(self, arg, from_tty):
+        frame = gdb.newest_frame()
+        total_size = 0
+        while frame:
+            sp = frame.read_register("sp")
+            frame_up = frame.older()
+            if not frame_up:
+                break
+            f = frame.function()
+            l = frame.level()
+            if l < 10:
+                l = "#" + str(l) + " "
+            else:
+                l = "#" + str(l)
+            size = frame_up.read_register("sp") - sp
+            total_size += size
+            print(l, sp, frame.type(), f, " " * (40 - len(str(f))), size)
+            # print(dir(f))
+            # Tweak this if for more detail for a specific function.
+            if False and f.name == "mp_execute_bytecode":
+                b = frame.block()
+                prev_b = None
+                while not b.is_static:
+                    print("  block", hex(b.start), hex(b.end), b.function)
+                    for sym in b:
+                        if not sym.needs_frame:
+                            continue
+                        v = sym.value(frame)
+                        print("   ", sym.addr_class, v.address, sym.type.sizeof, sym, sym.type, v)
+                    prev_b = b
+                    b = b.superblock
+
+                    if b.function == f:
+                        break
+                b = prev_b
+                print("pc scan", hex(b.start), hex(b.end))
+                seen = set()
+                for pc in range(b.start, b.end, 2):
+                    b = gdb.block_for_pc(pc)
+                    r = (b.start, b.end)
+                    if r in seen:
+                        continue
+                    seen.add(r)
+                    print(" ", hex(pc), hex(b.start), hex(b.end), b.function)
+                    for sym in b:
+                        if not sym.needs_frame:
+                            continue
+                        # if sym.type.sizeof <= 4:
+                        #     continue
+                        v = sym.value(frame)
+                        print("   ", sym.addr_class, v.address, sym.type.sizeof, sym, sym.type, v)
+            frame = frame_up
+        print("total size:", total_size)
+
+
+StackSize()

tools/stack-loc-to-pc.py

@@ -0,0 +1,28 @@
+"""Prints the pcs that access each stack location in a function. Useful for finding
+   infrequently used stack space.
+
+   Pipe in disassembly like so:
+
+   arm-none-eabi-objdump --disassemble=mp_execute_bytecode build-metro_m0_express/firmware.elf | python ../../tools/stack-loc-to-pc.py
+   """
+
+import sys
+import re
+
+offset = re.compile(r"sp, #(\d+)")
+
+offsets = {}
+for line in sys.stdin:
+    if "sp" in line:
+        m = offset.search(line)
+        o = int(m.groups()[0])
+        pc = line.split(":")[0]
+        if o not in offsets:
+            offsets[o] = []
+        offsets[o].append(pc.strip())
+
+print("Offset", "Size", "PCs", sep="\t")
+last_o = 0
+for o in sorted(offsets):
+    print(o, o - last_o, offsets[o], sep="\t")
+    last_o = o