[FREELDR] Adapt some assembly code for i386 position independent code (reactos#7530)

iLauncherDev · iLauncherDev · commit 1fcc18c8b37a · 2025-02-25T19:56:33.000-03:00
CORE-19882
diff --git a/boot/freeldr/freeldr/arch/realmode/fathelp.inc b/boot/freeldr/freeldr/arch/realmode/fathelp.inc
@@ -14,9 +14,13 @@
 #define BiosCHSDriveSizeHigh    6
 #define BiosCHSDriveSizeLow     8
 #define BiosCHSDriveSize        8
-#define ReadSectorsOffset       10
-#define ReadClusterOffset       12
-#define PutCharsOffset          14
+#define ReadSectorsOffset       12
+#define ReadClusterOffset       16
+#define PutCharsOffset          20
+
+#define ReadSectors far ptr ss:[bp-ReadSectorsOffset]
+#define ReadCluster far ptr ss:[bp-ReadClusterOffset]
+#define PutChars far ptr ss:[bp-PutCharsOffset]
 
 #define OEMName                 3
 #define BytesPerSector          11
@@ -65,8 +69,8 @@ FatHelperEntryPoint:
     push ax
 
     /* Display "Loading FreeLoader..." message */
-    mov si, offset msgLoading
-    call word ptr [bp-PutCharsOffset]
+    mov si, offset msgLoading 
+    call CS_PutChars
 
     call ReadFatIntoMemory
 
@@ -92,7 +96,7 @@ LoadFile3:
     push ax
     xor  bx,bx              // Load ROSLDR starting at 0000:8000h
     push es
-    call word ptr [bp-ReadClusterOffset]
+    call ReadCluster
     pop  es
 
     xor  bx,bx
@@ -133,7 +137,7 @@ ReadFatIntoMemory:
     mov bx, HEX(7000)
     mov es,bx
     xor bx,bx
-    call word ptr [bp-ReadSectorsOffset]
+    call ReadSectors
     ret
 
 
@@ -216,6 +220,22 @@ IsFat12_2:
 IsFat12_Done:
     ret
 
+CS_PutChars:
+    /* Save necessary registers */
+    push ax
+    push ds
+
+    /* Prepare ds before PutChars call */
+    mov ax, cs
+    mov ds, ax
+
+    /* Display the message */
+    call PutChars
+
+    /* Restore necessary registers and return */
+    pop ds
+    pop ax
+    ret
 
 msgLoading:
     .ascii "Loading FreeLoader...", CR, LF, NUL
diff --git a/boot/freeldr/freeldr/arch/realmode/helpers.inc b/boot/freeldr/freeldr/arch/realmode/helpers.inc
@@ -144,7 +144,7 @@ Relocator16Boot:
     and cx, not (EFLAGS_CF or EFLAGS_ZF or EFLAGS_SF)
 
     /* Get flags CF, ZF and SF from the REGS structure */
-    mov ax, word ptr cs:[BSS_RegisterSet + REGS_EFLAGS]
+    mov ax, word ptr ss:[BSS_RegisterSet + REGS_EFLAGS]
     and ax, (EFLAGS_CF or EFLAGS_ZF or EFLAGS_SF)
 
     /* Combine flags and set them */
@@ -153,36 +153,47 @@ Relocator16Boot:
     popf
 
     /* Setup the segment registers */
-    mov ax, word ptr cs:[BSS_RegisterSet + REGS_DS]
+    mov ax, word ptr ss:[BSS_RegisterSet + REGS_DS]
     mov ds, ax
-    mov ax, word ptr cs:[BSS_RegisterSet + REGS_ES]
+    mov ax, word ptr ss:[BSS_RegisterSet + REGS_ES]
     mov es, ax
-    mov ax, word ptr cs:[BSS_RegisterSet + REGS_FS]
+    mov ax, word ptr ss:[BSS_RegisterSet + REGS_FS]
     mov fs, ax
-    mov ax, word ptr cs:[BSS_RegisterSet + REGS_GS]
+    mov ax, word ptr ss:[BSS_RegisterSet + REGS_GS]
     mov gs, ax
 
     /* Patch the jump address (segment:offset) */
-    mov eax, dword ptr cs:[BSS_RealModeEntry]
+    mov eax, dword ptr ss:[BSS_RealModeEntry]
     mov dword ptr cs:[Relocator16Address], eax
 
-    /* Switch the stack (segment:offset) */
+    /* Store the stack (segment:offset) */
     mov eax, dword ptr cs:[BSS_CallbackReturn]
     shr eax, 16
-    mov ss, ax
+    mov word ptr cs:[Relocator16SS], ax
     mov eax, dword ptr cs:[BSS_CallbackReturn]
     and eax, HEX(0FFFF)
-    mov esp, eax
+    mov dword ptr cs:[Relocator16ESP], eax
 
     /* Setup the registers */
-    mov eax, dword ptr cs:[BSS_RegisterSet + REGS_EAX]
-    mov ebx, dword ptr cs:[BSS_RegisterSet + REGS_EBX]
-    mov ecx, dword ptr cs:[BSS_RegisterSet + REGS_ECX]
-    mov edx, dword ptr cs:[BSS_RegisterSet + REGS_EDX]
-    mov esi, dword ptr cs:[BSS_RegisterSet + REGS_ESI]
-    mov edi, dword ptr cs:[BSS_RegisterSet + REGS_EDI]
+    mov eax, dword ptr ss:[BSS_RegisterSet + REGS_EAX]
+    mov ebx, dword ptr ss:[BSS_RegisterSet + REGS_EBX]
+    mov ecx, dword ptr ss:[BSS_RegisterSet + REGS_ECX]
+    mov edx, dword ptr ss:[BSS_RegisterSet + REGS_EDX]
+    mov esi, dword ptr ss:[BSS_RegisterSet + REGS_ESI]
+    mov edi, dword ptr ss:[BSS_RegisterSet + REGS_EDI]
     // Don't setup ebp, we only use it as output! <-- FIXME!
 
+    /* Save eax */
+    mov dword ptr cs:[Relocator16EAX], eax
+
+    /* Switch the stack (segment:offset) */
+    mov esp, dword ptr cs:[Relocator16ESP]
+    mov ax, word ptr cs:[Relocator16SS]
+    mov ss, ax
+
+    /* Restore eax */
+    mov eax, dword ptr cs:[Relocator16EAX]
+
     /* Jump to the new CS:IP (e.g. jump to bootsector code...) */
     .byte HEX(0EA) // ljmp16 segment:offset
 Relocator16Address:
diff --git a/boot/freeldr/freeldr/arch/realmode/helpers_pc98.inc b/boot/freeldr/freeldr/arch/realmode/helpers_pc98.inc
@@ -207,35 +207,46 @@ Relocator16Boot:
     popf
 
     /* Setup the segment registers */
-    mov ax, word ptr cs:[BSS_RegisterSet + REGS_DS]
+    mov ax, word ptr ss:[BSS_RegisterSet + REGS_DS]
     mov ds, ax
-    mov ax, word ptr cs:[BSS_RegisterSet + REGS_ES]
+    mov ax, word ptr ss:[BSS_RegisterSet + REGS_ES]
     mov es, ax
-    mov ax, word ptr cs:[BSS_RegisterSet + REGS_FS]
+    mov ax, word ptr ss:[BSS_RegisterSet + REGS_FS]
     mov fs, ax
-    mov ax, word ptr cs:[BSS_RegisterSet + REGS_GS]
+    mov ax, word ptr ss:[BSS_RegisterSet + REGS_GS]
     mov gs, ax
 
     /* Patch the jump address (segment:offset) */
-    mov eax, dword ptr cs:[BSS_RealModeEntry]
+    mov eax, dword ptr ss:[BSS_RealModeEntry]
     mov dword ptr cs:[Relocator16Address], eax
 
-    /* Switch the stack (segment:offset) */
+    /* Store the stack (segment:offset) */
     mov eax, dword ptr cs:[BSS_CallbackReturn]
     shr eax, 16
-    mov ss, ax
+    mov word ptr cs:[Relocator16SS], ax
     mov eax, dword ptr cs:[BSS_CallbackReturn]
     and eax, HEX(0FFFF)
-    mov esp, eax
+    mov dword ptr cs:[Relocator16ESP], eax
 
     /* Setup the registers */
-    mov eax, dword ptr cs:[BSS_RegisterSet + REGS_EAX]
-    mov ebx, dword ptr cs:[BSS_RegisterSet + REGS_EBX]
-    mov ecx, dword ptr cs:[BSS_RegisterSet + REGS_ECX]
-    mov edx, dword ptr cs:[BSS_RegisterSet + REGS_EDX]
-    mov esi, dword ptr cs:[BSS_RegisterSet + REGS_ESI]
-    mov edi, dword ptr cs:[BSS_RegisterSet + REGS_EDI]
-    mov ebp, dword ptr cs:[BSS_RegisterSet + REGS_EBP]
+    mov eax, dword ptr ss:[BSS_RegisterSet + REGS_EAX]
+    mov ebx, dword ptr ss:[BSS_RegisterSet + REGS_EBX]
+    mov ecx, dword ptr ss:[BSS_RegisterSet + REGS_ECX]
+    mov edx, dword ptr ss:[BSS_RegisterSet + REGS_EDX]
+    mov esi, dword ptr ss:[BSS_RegisterSet + REGS_ESI]
+    mov edi, dword ptr ss:[BSS_RegisterSet + REGS_EDI]
+    mov ebp, dword ptr ss:[BSS_RegisterSet + REGS_EBP]
+
+    /* Save eax */
+    mov dword ptr cs:[Relocator16EAX], eax
+
+    /* Switch the stack (segment:offset) */
+    mov esp, dword ptr cs:[Relocator16ESP]
+    mov ax, word ptr cs:[Relocator16SS]
+    mov ss, ax
+
+    /* Restore eax */
+    mov eax, dword ptr cs:[Relocator16EAX]
 
     /* Jump to the new CS:IP */
     .byte HEX(0EA) /* ljmp16 segment:offset */
diff --git a/boot/freeldr/freeldr/arch/realmode/i386.S b/boot/freeldr/freeldr/arch/realmode/i386.S
@@ -25,54 +25,55 @@ RealModeEntryPoint:
     mov ss, ax
 
     /* Setup the stack */
-    mov sp, word ptr ds:[stack16]
+    mov sp, STACK16ADDR
 
     /* Enable A20 address line */
     call EnableA20
 
+    /* Update BSS_CurrentBaseAddress, instruction pointer and code segment */
+    call UpdateCurrentCodeSegment
+
+    /* Output first status */
+    mov si, offset Msg_Starting
+    call cs_writestr
+
     /* Save real mode entry point in shared memory */
-    mov dword ptr ds:[BSS_RealModeEntry], offset switch_to_real16
+    mov dword ptr ds:[BSS_RealModeEntry], offset switch_to_real16 + FREELDR_BASE
 
     /* Address the image with es segment */
-    mov ax, FREELDR_PE_BASE / 16
+    mov ax, cs
+    add ax, (FREELDR_PE_BASE - FREELDR_BASE) / 16
     mov es, ax
 
     /* Get address of optional header */
     mov eax, dword ptr es:[IMAGE_DOS_HEADER_e_lfanew]
     add eax, 4 + IMAGE_FILE_HEADER_SIZE
 
-    /* Get address of entry point */
+    /* Get offset of entry point */
     mov eax, dword ptr es:[eax + IMAGE_OPTIONAL_HEADER_AddressOfEntryPoint]
-    add eax, FREELDR_PE_BASE
 
     /* Save entry point */
-    mov dword ptr ds:[pm_entrypoint], eax
+    mov dword ptr cs:[pm_entrypoint], eax
 
     /* Restore es */
     xor ax, ax
     mov es, ax
 
     jmp exit_to_protected
 
+Msg_Starting:
+    .ascii "Starting FreeLoader...", CR, LF, NUL
 
 /* This is the entry point from protected mode */
 switch_to_real16:
 
-    /* Restore segment registers to correct limit */
-    mov ax, RMODE_DS
-    mov ds, ax
-    mov es, ax
-    mov fs, ax
-    mov gs, ax
-    mov ss, ax
-
     /* Disable Protected Mode */
     mov eax, cr0
     and eax, CR0_PE_CLR
     mov cr0, eax
 
     /* Clear prefetch queue & correct CS */
-    ljmp16 0, inrmode
+    ljmp16 FREELDR_BASE / 16, inrmode
 
 inrmode:
     /* Set real mode segments */
@@ -92,20 +93,16 @@ inrmode:
     xor esp, esp
 
     /* Restore real mode stack */
-    mov sp, word ptr ds:[stack16]
+    mov sp, word ptr cs:[stack16]
 
     /* Load IDTR with real mode value */
-#ifdef _USE_ML
-    lidt fword ptr rmode_idtptr
-#else
-    lidt rmode_idtptr
-#endif
+    lidt lXdtPrefix cs:[rmode_idtptr]
 
     sti /* These are ok now */
 
     /* Do the callback, specified by bx */
     shl bx, 1
-    call word ptr ds:CallbackTable[bx]
+    call word ptr cs:CallbackTable[bx]
 
 
 /*
@@ -117,28 +114,54 @@ exit_to_protected:
     cli
 
     /* Save current stack pointer */
-    mov word ptr ds:[stack16], sp
+    mov word ptr cs:[stack16], sp
+
+    /* Set ds to cs segment register */
+    mov ax, cs
+    mov ds, ax
+
+    /* Copy the gdt entries to GDTDATA_BASE */
+    mov cx, offset gdt_end - gdt
+    mov si, offset gdt
+    mov di, GDTDATA_BASE
+    rep movsb
+
+    /* Copy the protected mode code to TEMPCODE16_BASE */
+    mov cx, offset pm_entrypoint_end - inpmode
+    mov si, offset inpmode
+    mov di, TEMPCODE16_BASE
+    rep movsb
+
+    /* Convert the entry point offset to absolute address */
+    mov eax, dword ptr ss:[BSS_CurrentBaseAddress]
+    add eax, FREELDR_PE_BASE - FREELDR_BASE
+    add dword ptr ss:[(pm_entrypoint - inpmode) + TEMPCODE16_BASE], eax
+
+    /* Reset ds */
+    xor ax, ax
+    mov ds, ax
 
     /* Load the GDT */
-#ifdef _USE_ML
-    lgdt fword ptr gdtptr
-#else
-    lgdt gdtptr
-#endif
+    lgdt lXdtPrefix cs:[gdtptr]
 
     /* Enable Protected Mode */
     mov eax, cr0
     or eax, CR0_PE_SET
     mov cr0, eax
 
     /* Clear prefetch queue & correct CS */
-    ljmp16 PMODE_CS, inpmode
+    ljmp16 PMODE_CS, TEMPCODE16_BASE
 inpmode:
     .byte HEX(0ff), HEX(25) // opcode of indirect jump
-    .word pm_entrypoint, 0
+#ifdef _USE_ML
+    .long (offset pm_entrypoint - inpmode) + TEMPCODE16_BASE
+#else
+    .long (pm_entrypoint - inpmode) + TEMPCODE16_BASE
+#endif
 pm_entrypoint:
     .long 0 // receives address of PE entry point
     nop
+pm_entrypoint_end:
 
 /* FNID_* functions */
 CallbackTable:
@@ -176,22 +199,23 @@ gdt:
     .word HEX(9200)
     .word HEX(00CF)
 
-    /* 16-bit real mode CS */
+    /* 16-bit flat CS (!) */
     .word HEX(FFFF)
     .word HEX(0000)
-    .word HEX(9E00)
-    .word HEX(0000)
+    .word HEX(9B00)
+    .word HEX(008F)
 
     /* 16-bit real mode DS */
     .word HEX(FFFF)
     .word HEX(0000)
     .word HEX(9200)
     .word HEX(0000)
+gdt_end:
 
 /* GDT table pointer */
 gdtptr:
     .word HEX(27)       /* Limit */
-    .word gdt, 0        /* Base Address */
+    .long GDTDATA_BASE  /* Base Address */
 
 /* Real-mode IDT pointer */
 rmode_idtptr:
diff --git a/boot/freeldr/freeldr/arch/realmode/int386.inc b/boot/freeldr/freeldr/arch/realmode/int386.inc
