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const bios = @import("bios.zig");
// -- ENTRY POINT ---------------------------------------------------------------
export fn _entry() linksection(".boot") callconv(.Naked) noreturn {
asm volatile (
// Disable interrupts.
\\cli
// Clear segment selectors.
\\xor %%ax, %%ax
\\mov %%ax, %%ds
\\mov %%ax, %%es
\\mov %%ax, %%ss
\\mov %%ax, %%fs
\\mov %%ax, %%gs
\\mov $0x7c00, %sp
// Long jump to set cs to 0x0000, as some BIOSes load the MBR
// to either 07c0:0000 or 0000:7c000.
\\ljmp $0x0, $main
);
}
// -- MAIN ----------------------------------------------------------------------
// main should be "callconv(.naked)", once issue is fixed.
// https://github.com/ziglang/zig/issues/18183
export fn main() noreturn {
dump_memmap();
while (true) {
asm volatile ("hlt");
}
}
// -- UTILS ---------------------------------------------------------------------
fn dump_memmap() void {
// Keep track of continuatation code.
var off: u32 = 0;
// Accumulated free/usable memory.
var mem: u64 = 0;
// Iterate over E820 entries.
while (bios.e820(off)) |entry| : (off = entry.ebx) {
puts_hex(entry.e820.base);
bios.putc('-');
puts_hex(entry.e820.size);
bios.putc('-');
puts_hex(entry.e820.kind);
bios.putc('-');
puts_hex(entry.e820.attr);
bios.putc('\n');
// Accumulate free, useable memory.
if (entry.e820.kind == 1 and entry.e820.attr == 1) {
mem += entry.e820.size;
}
// All E820 entries retrieved, continuing would start from the beginning.
if (entry.ebx == 0) {
break;
}
}
// Report total free memory in MBs.
bios.putc('m');
bios.putc('=');
puts_hex(mem / 1024 / 1024);
}
fn puts(str: []const u8) void {
for (str) |c| {
bios.putc(c);
}
}
fn puts_hex(init_val: u64) void {
if (init_val == 0) {
bios.putc('0');
return;
}
var val = init_val;
var buf: [32]u8 = undefined;
var idx = buf.len;
while (val > 0 and idx != 0) : (val /= 16) {
idx -= 1;
const digit = switch (@as(u8, @truncate(val % 16))) {
0...9 => |d| '0' + d,
10...15 => |d| 'a' + d - 10,
else => '?',
};
buf[idx] = digit;
}
puts(buf[idx..]);
}
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