asm startup incomplete, but can boot a tiny example.

.cargo/config.toml

@@ -3,12 +3,10 @@ target = "thumbv4t-none-eabi"
 
 [unstable]
 build-std = ["core"]
-build-std-features = ["compiler-builtins-weak-intrinsics"]
 
 [target.thumbv4t-none-eabi]
 runner = "mgba-qt"
 rustflags = [
   "-Clinker=arm-none-eabi-ld",
   "-Clink-arg=-Tlinker_scripts/mono_boot.ld",
-  "--emit=mir",
 ]

.github/workflows/ci-builds.yml

@@ -34,3 +34,6 @@ jobs:
 
       - name: Build The Examples (Link With LLD, strong compiler intrinsics)
         run: cargo build --examples --target=thumbv4t-none-eabi -Zbuild-std=core -Clink-arg=-Tlinker_scripts/mono_boot.ld
+
+      - name: Build The Crate With No Default Features (build script usage simulation)
+        run: cargo build --no-default-features

Cargo.toml

@@ -7,19 +7,35 @@ edition = "2021"
 license = "Zlib OR Apache-2.0 OR MIT"
 
 [features]
-default = ["on_gba", "critical-section", "doc_cfg"]
+default = ["on_gba"]
 # SEE THE CRATE DOCS FOR SAFETY RELATED INFO REGARDING THIS FEATURE.
 on_gba = []
-# utilize `doc_cfg` where appropriate. requires nightly.
+# utilize `doc_cfg` where appropriate. requires nightly. intended mostly for use
+# during docs.rs documentation generation.
 doc_cfg = []
+# Activates the `track_caller` attribute on various functions. Use of the
+# `track_caller` attribute on a function adds a "secret" extra argument for the
+# `Location` of the caller, which can reduce performance if the function is not
+# inlined (meaning  `Location` is passed via the stack). This is only needed for
+# debugging, and so it's off by default.
 track_caller = []
+# The assembly runtime's irq handler will take extra steps to allow nested
+# interrupts during calls to the Rust interrupt handler, and also the Rust
+# interrupt handler will be called with the CPU in System mode, allowing for
+# full stack usage. If you do not use this feature then the Rust IRQ handler
+# will be called with the CPU in IRQ mode with nested interrupts disabled at the
+# CPU level. IRQ mode still has enough stack space to do any *reasonable* IRQ
+# handling, so you do NOT normally need to use this unless you need nested
+# interrupt support or extremely large stack usage during the handler.
+robust_irq_handler = []
 
 [dependencies]
 voladdress = "1.3.0"
 bitfrob = "1"
 critical-section = { version = "1.1.2", features = [
   "restore-state-bool",
 ], optional = true }
+bytemuck = { version = "1.16.0", optional = true }
 
 [profile.dev]
 opt-level = 3
@@ -38,3 +54,4 @@ incremental = false
 # on the GBA. This is the closest target that docs.rs supports by default and
 # which *also* supports the `instruction_set` attribute to avoid build errors.
 targets = ["armv5te-unknown-linux-gnueabi"]
+features = ["doc_cfg"]

dump.bat

@@ -0,0 +1,2 @@
+cargo build --examples
+arm-none-eabi-objdump --headers --disassemble --demangle --architecture=armv4t --no-show-raw-insn -Mreg-names-std target/thumbv4t-none-eabi/debug/examples/do_nothing >target/ex-do_nothing.txt

examples/do_nothing.rs

@@ -0,0 +1,9 @@
+#![no_std]
+#![no_main]
+
+gba::panic_handler!(empty_loop);
+
+#[no_mangle]
+pub extern "C" fn main() -> ! {
+  loop {}
+}

linker_scripts/mono_boot.ld

@@ -1,6 +1,6 @@
 /* THIS LINKER SCRIPT FILE IS RELEASED TO THE PUBLIC DOMAIN (SPDX: CC0-1.0) */
 
-ENTRY(__start)
+ENTRY(_start)
 
 MEMORY {
   ewram (w!x) : ORIGIN = 0x2000000, LENGTH = 256K
@@ -11,7 +11,7 @@ MEMORY {
 SECTIONS {
   .text : {
     /* be sure that the ROM header is the very first */
-    *(.text.gba_rom_header);
+    *(.text._start);
     *(.text .text.*);
     . = ALIGN(4);
   } >rom = 0x00
@@ -22,42 +22,42 @@ SECTIONS {
   } >rom = 0x00
 
   . = ALIGN(4);
-  __iwram_position_in_rom = .;
+  _iwram_position_in_rom = .;
   .data : {
-    __iwram_start = ABSOLUTE(.);
+    _iwram_start = ABSOLUTE(.);
 
     *(.data .data.*);
     *(.iwram .iwram.*);
     . = ALIGN(4);
 
-    __iwram_end = ABSOLUTE(.);
+    _iwram_end = ABSOLUTE(.);
   } >iwram AT>rom = 0x00
 
   . = ALIGN(4);
-  __ewram_position_in_rom = __iwram_position_in_rom + (__iwram_end - __iwram_start);
+  _ewram_position_in_rom = _iwram_position_in_rom + (_iwram_end - _iwram_start);
   .ewram : {
-    __ewram_start = ABSOLUTE(.);
+    _ewram_start = ABSOLUTE(.);
 
     *(.ewram .ewram.*);
     . = ALIGN(4);
 
-    __ewram_end = ABSOLUTE(.);
+    _ewram_end = ABSOLUTE(.);
   } >ewram AT>rom = 0x00
 
   . = ALIGN(4);
-  __bss_position_in_rom = __ewram_position_in_rom + (__ewram_end - __ewram_start);
+  _bss_position_in_rom = _ewram_position_in_rom + (_ewram_end - _ewram_start);
   .bss : {
-    __bss_start = ABSOLUTE(.);
+    _bss_start = ABSOLUTE(.);
 
     *(.bss .bss.*);
     . = ALIGN(4);
 
-    __bss_end = ABSOLUTE(.);
+    _bss_end = ABSOLUTE(.);
   } >iwram
 
-  __iwram_word_copy_count = (__iwram_end - __iwram_start) / 4;
-  __ewram_word_copy_count = (__ewram_end - __ewram_start) / 4;
-  __bss_word_clear_count = (__bss_end - __bss_start) / 4;
+  _iwram_word_copy_count = (_iwram_end - _iwram_start) / 4;
+  _ewram_word_copy_count = (_ewram_end - _ewram_start) / 4;
+  _bss_word_clear_count = (_bss_end - _bss_start) / 4;
 
   /* rust-lld demands we keep the `section header string table` */
   .shstrtab        0 : { *(.shstrtab) }