add custom post-build script

Rust doesn't support those natively.

scripts/build.py

@@ -0,0 +1,53 @@
+#!/usr/bin/env python3
+
+# DISCLAIMER: I don't know python.  And i don't like python.
+# This is only written in python because pretty much everyone already has it
+# installed and rust doesn't support post-build scripts for some reason.
+
+import sys
+from utils import crc32, run_sync
+
+if len(sys.argv) >= 2:
+    PROFILE = sys.argv[1]
+else:
+    PROFILE = "debug"
+
+
+def finalize_stage1(filename: str):
+    run_sync(
+        "objcopy", "-O", "binary",
+        "target/x86-pc-none/" + PROFILE + "/bussy-stage1",
+        filename
+    )
+
+    with open(filename, "r+b") as file:
+        data = bytearray(file.read())
+
+        size = len(data)
+        if size > 0x8000:
+            print("stage1 is too big (greater than 32 K)")
+            exit(1)
+        data[2] = size & 0xff
+        data[3] = size >> 8
+
+        csum = crc32(data)
+        print("CRC32 checksum of stage1 is " + hex(csum))
+        data[4] = csum & 0xff
+        data[5] = (csum >> 8) & 0xff
+        data[6] = (csum >> 16) & 0xff
+        data[7] = csum >> 24
+
+        file.seek(2)
+        file.write(data[2:8])
+
+
+print("Running cargo")
+if PROFILE == "debug":
+    run_sync("cargo", "build", "--workspace")
+elif PROFILE == "release":
+    run_sync("cargo", "build", "--workspace", "--release")
+else:
+    run_sync("cargo", "build", "--workspace", "--profile", PROFILE)
+
+print("Finalizing stage1")
+finalize_stage1("target/x86-pc-none/" + PROFILE + "/stage1.bin")

scripts/utils.py

@@ -0,0 +1,49 @@
+# Miscellaneous utilities, meant to be included from build.py
+
+import os
+
+
+# Do a fork/execl because that way all children get the same stdout,
+# i.e. if it's a tty the executed program should behave appropriately.
+# Python probably has an idiomatic way to do this, but frankly idc.
+def run_sync(program: str, *args):
+    path = os.popen("which " + program).read().strip()
+    child = os.fork()
+    if child == 0:
+        os.execl(path, program, *args)
+        print("execl() failed")
+        exit(1)
+    elif child == -1:
+        print("fork() failed")
+        exit(1)
+    status = os.waitpid(child, 0)
+    if status[1] != 0:
+        print(program + " exited with status code " + str(status[1]))
+        exit(1)
+
+
+def generate_crc_tab(poly_reverse: int):
+    tab = []
+    for crc in range(256):
+        for _ in range(8):
+            lsb = crc % 2
+            crc >>= 1
+            if lsb == 1:
+                crc ^= poly_reverse
+        tab.append(crc)
+    return tab
+
+
+def do_crc(data, table):
+    crc = 0xffffffff
+    for byte in data:
+        crc = (crc >> 8) ^ table[(crc ^ byte) & 0xff]
+    return ~crc & 0xffffffff
+
+
+CCITT32_TAB = generate_crc_tab(0xedb88320)
+
+
+def crc32(data: bytes):
+    global CCITT32_TAB
+    return do_crc(data, CCITT32_TAB)