cap bss, clean up some padding issues and clean up sign section

docs/Stevia Notes.md

@@ -207,24 +207,45 @@ Each GDT entry is 8 bytes:
 
 ## **5. Memory Layout Example**
 
-### **Low Memory (First MiB)**
+### **Low Memory/Upper Memory map (<= 1MiB)**
 
-| Start       | End         | Size            | Type                  | Description                      |
+| Start       | End         | Size            | Type                 | Description                    |
-|-------------|-------------|-----------------|-----------------------|----------------------------------|
+|-------------|-------------|-----------------|----------------------|--------------------------------|
-| 0x00000000  | 0x000003FF  | 1 KiB           | RAM (partially unusable) | Real Mode IVT (Interrupt Vector Table) |
+| 0x00000000  | 0x000003FF  | 1 KiB           | RAM reclaimable~1~   | Real Mode IVT                  |
-| 0x00000400  | 0x000004FF  | 256 bytes       | RAM (partially unusable) | BDA (BIOS data area)             |
+| 0x00000400  | 0x000004FF  | 256 bytes       | RAM reclaimable~1~   | BDA                            |
-| 0x00000500  | 0x00007BFF  | almost 30 KiB   | RAM - free for use     | Conventional memory              |
+| 0x00000500  | 0x00007BFF  | 29 KiB + 767b   | RAM - free           | Conventional memory            |
-| 0x00007C00  | 0x00007DFF  | 512 bytes       | RAM (partially unusable) | OS BootSector                    |
+| 0x00007C00  | 0x00007DFF  | 512 bytes       | RAM reclaimable~2~   | OS BootSector                  |
-| 0x00007E00  | 0x0007FFFF  | 480.5 KiB       | RAM - free for use     | Conventional memory              |
+| 0x00007E00  | 0x0007FFFF  | 480.5 KiB       | RAM - free           | Conventional memory            |
-| 0x00080000  | 0x0009FFFF  | 128 KiB         | RAM (partially unusable) | EBDA (Extended BIOS Data Area)   |
+| 0x00080000  | 0x0009FFFF  | 128 KiB         | RAM (unusable)~1~    | EBDA (Extended BIOS Data Area) |
-| 0x000A0000  | 0x000FFFFF  | 384 KiB         | various (unusable)     | Video memory, ROM Area           |
+| 0x000A0000  | 0x000FFFFF  | 384 KiB         | Upper RAM (unusable) | Video memory, ROM Area         |
 
-### **Extended Memory (Above 1 MiB)**
+1. Reclaimable in the event that you *never* need the BIOS again & once the CPU is in protected mode.
+2. Reclaimable after you are done with with the MBR/VBR stages.
 
-| Start       | End         | Size            | Description            |
+### **Extended Memory (> 1 MiB)**
-|-------------|-------------|-----------------|------------------------|
+
-| 0x00100000  | 0x00EFFFFF  | 14 MiB          | RAM - free for use     |
+This is only an example, you should always check the memory map.
+
+| Start       | End         | Size            | Description                           |
+|-------------|-------------|-----------------|---------------------------------------|
+| 0x00100000  | 0x00EFFFFF  | 14 MiB          | RAM(?) - free for use                    |
 | 0x00F00000  | 0x00FFFFFF  | 1 MiB           | Possible memory-mapped hardware (ISA) |
-| 0x01000000  | ?           | ?               | More extended memory   |
+| 0x01000000  | ?           | ?               | More extended memory                  |
 | 0xC0000000  | 0xFFFFFFFF  | 1 GiB           | Memory mapped PCI devices, BIOS, etc. |
-| 0x0000000100000000 | ?     | ?               | RAM - usable in PAE/64-bit mode |
+| 0x0000000100000000 | ?    | ?               | RAM(?) - usable in PAE/64-bit mode      |
+
+
+## **6. Stage2 Memory Layout  **
+
+Overall, Tiny (64 KiB page) Code/Data, Flat 4GiB mapping in gs/fs after unreal switch
+
+| Start       | End         | Size (Bytes) | Type               | Description                |
+|-------------|-------------|--------------|--------------------|----------------------------|
+| 0x00000000  | 0x000003FF  | 0x400        | RAM - (BIOS)       | Real Mode IVT              |
+| 0x00000400  | 0x000004FF  | 0x100        | RAM - (BIOS)       | BDA                        |
+| 0x00000500  | 0x000042FF  | 0x3E00       | RAM - .text/.data  | Code and constants/strings |
+| 0x00004300  | 0x000044FF  | 0x100        | RAM - .sign        | EOF marker/signature       |
+| 0x00004500  | 0x000074FF  | 0x3000       | RAM - bss          | Runtime data/stack         |
+| 0x00007500  | 0x00007FFF  | 0xB00        | RAM - reserved     | Reserved                   |
+| 0x00008000  | 0x0000DFFF  | 0x6000       | RAM - heap         | Conventional memory        |
+| 0x0000F000  | 0x0000FFFF  | 0x1000       | RAM - reserved     | Reserved                   |

include/config.inc

@@ -15,7 +15,7 @@
 
 %ifndef __INC_STEVIA_CONFIG
 
-%define SECTOR_SIZE             512
+%define SECTOR_SIZE            0x200
 %define STAGE2_SECTOR_COUNT    0x20
 ; 16 KiB
 %define MAX_STAGE2_BYTES      (SECTOR_SIZE * STAGE2_SECTOR_COUNT)

src/stage2/stage2.nasm

@@ -36,7 +36,7 @@
 section .text
 begin_text:
 ; dl = byte boot_drive
-ALIGN 4, db 0x90
+ALIGN 16, db 0x90
 init:
     cli                               ; We do not want to be interrupted
     mov [boot_drive], dl              ; copy boot_drive to globals
@@ -375,7 +375,8 @@ EnterUnrealMode:
 end_text:
 
 section .data follows=.text
-align 512
+align 16, db 0
+
 begin_data:
 ; #############
 ;
@@ -410,19 +411,15 @@ define_info MaybeFound_Boot, "Maybe found a file...checking..."
 
 define_cstr BootTarget, "BOOT    BIN"
 
-align 16, db 0
-BootTarget:
-    db 'BOOT    BIN'
-
-;
-; pre-bss init globals
-;
-
 ; set to boot_drive passed from BIOS almost first thing in init
 align 4, db 0
 boot_drive:
     db 0x00
 
+align 16, db 0
+BootTarget:
+    db 'BOOT    BIN'
+
 align 16, db 0
 IntToHex_table:
     db '0123456789ABCDEF'
@@ -504,15 +501,20 @@ BUILD_GIT_HASH:
     db __GIT_HASH__, 00h
 end_data:
 
-%assign bytes_remaining ((MAX_STAGE2_BYTES - 512) - (($ - $$) + (end_text - begin_text)))
+%define SIG_BYTES 0x4
-%warning STAGE2 has bytes_remaining bytes remaining for code/data (MAX: MAX_STAGE2_BYTES)
+
+; Optional: fail fast if we overflowed
+%if ((MAX_STAGE2_BYTES - 512) - (($ - $$) + (end_text - begin_text))) < 0
+    %error "Stage2 overflow: code+data exceed MAX_STAGE2_BYTES - SIG_BYTES"
+%endif
 
 ; section start location needs to be a 'critical expression'
 ; i.e resolvable at build time, we are setting 0x0500 as the offset since
 section .sign start=((MAX_STAGE2_BYTES - 512) + 0x0500)
 times ((512 - 4) - ($ -$$) ) db 0x90     ; nop
 STAGE2_SIG: dd 0xDEADBEEF                ; Signature to mark the end of the stage2
-
+; !!! END Stage2 .text/.data !!!
+align 16, resb 1
 section .bss follows=.sign
 begin_bss:
 
@@ -596,3 +598,11 @@ stack_bottom:
     resb 1024
 stack_top:
 end_bss:
+
+; Pad to the cap (emits nothing in the file; only increases .bss virtual size).
+; If BSS_SIZE > BSS_MAX_BYTES, this becomes negative and NASM errors out.
+%define BSS_MAX_BYTES 0x3000
+resb (BSS_MAX_BYTES - (end_bss - begin_bss))
+
+; Optional: keep a label for later math:
+bss_cap_end: