better startup: all zig, bss and data init'd

build.zig

@@ -10,14 +10,13 @@ pub fn build(b: *std.Build) void {
 
     const exe = b.addExecutable(.{
         .name = "stm32",
-        .root_source_file = b.path("src/main.zig"),
+        .root_source_file = b.path("src/startup.zig"),
         .target = target,
         //.optimize = .Debug,
         .optimize = .ReleaseSafe,
         .linkage = .static,
     });
 
-    exe.addAssemblyFile(b.path("src/bootstrap.s"));
     exe.setLinkerScriptPath(b.path("link.ld"));
 
     b.installArtifact(exe);

link.ld

@@ -23,24 +23,24 @@ SECTIONS {
 	} > FLASH
 
 	/* initialized data */
-	_sidata = LOADADDR(.data);
+	__data_flash = LOADADDR(.data);
 	.data : {
 		. = ALIGN(8);
-		_sdata = .;
+		__data = .;
 		*(.data)
 		*(.data*)
 		. = ALIGN(8);
-		_edata = .;
+		__data_size = . - __data;
 	} > RAM AT > FLASH
 
 	/* uninitialized data */
 	.bss : {
 		. = ALIGN(8);
-		_sbss = .;
+		__bss = .;
 		*(.bss)
 		*(.bss*)
 		. = ALIGN(8);
-		_ebss = .;
+		__bss_size = . - __bss;
 	} > RAM
 
 	.stack : {

src/bootstrap.s

@@ -1,13 +0,0 @@
-.cpu cortex-m4
-.thumb
-
-.extern _start
-.extern _tstack
-
-.section .vector_table
-.global init_vector_table
-init_vector_table:
-    .word _tstack
-    .word _start
-    .skip 4 * 14
-

src/main.zig

@@ -8,7 +8,7 @@ const gpioa = gpio.gpioa;
 const gpioc = gpio.gpioc;
 const tick = timer.systick;
 
-export fn _start() callconv(.C) noreturn {
+pub fn main() void {
     cpu.interrupt_disable();
     interrupt.initialize();
     interrupt.register(.SVCall, svcall);

src/startup.zig

@@ -0,0 +1,41 @@
+const main = @import("main.zig");
+
+extern const __data_flash: u32;
+extern const __data: u32;
+extern const __data_size: u32;
+extern const __bss: u32;
+extern const __bss_size: u32;
+
+comptime {
+    asm (
+        \\.extern _start
+        \\.extern _tstack
+        \\
+        \\.section .vector_table
+        \\.global init_vector_table
+        \\init_vector_table:
+        \\    .word _tstack
+        \\    .word _start
+        \\    .skip 4 * 14
+    );
+}
+
+inline fn zero_bss() void {
+    const bss: [*]volatile u8 = @ptrFromInt(@intFromPtr(&__bss));
+    @memset(bss[0..@intFromPtr(&__bss_size)], 0);
+}
+
+inline fn copy_data() void {
+    const data_flash: [*]volatile u8 = @ptrFromInt(@intFromPtr(&__data_flash));
+    const data: [*]volatile u8 = @ptrFromInt(@intFromPtr(&__data));
+    const data_size = @intFromPtr(&__data_size);
+    @memcpy(data[0..data_size], data_flash[0..data_size]);
+}
+
+export fn _start() callconv(.C) noreturn {
+    zero_bss();
+    copy_data();
+    main.main();
+    while (true) {}
+}
+