Implement relocation tables in KEXC binaries

Author: Noam Preil

doc/kexc

@@ -35,15 +35,16 @@ good idea.
 
 The following headers are defined in kernel.inc:
 
-    Name                Description
-
-    KEXC_HEADER_END     The end of the header list. Value may be omitted.
-    KEXC_ENTRY_POINT    Pointer to executable entry point.
-    KEXC_STACK_SIZE     Bytes of stack required, divided by two.
-    KEXC_KERNEL_VER     Minimum kernel version supported. Major, minor.
-    KEXC_THREAD_FLAGS   Thread flags. Only the upper 8 bits are considered.
-    KEXC_NAME           Pointer to program name.
-    KEXC_DESCRIPTION    Pointer to program description.
+    Name                  Description
+
+    KEXC_HEADER_END       The end of the header list. Value may be omitted.
+    KEXC_ENTRY_POINT      Pointer to executable entry point.
+    KEXC_STACK_SIZE       Bytes of stack required, divided by two.
+    KEXC_KERNEL_VER       Minimum kernel version supported. Major, minor.
+    KEXC_THREAD_FLAGS     Thread flags. Only the upper 8 bits are considered.
+    KEXC_NAME             Pointer to program name.
+    KEXC_DESCRIPTION      Pointer to program description.
+    KEXC_RELOCATION_TABLE Pointer to the relocation table.
 
 Header keys are numbered from 0x00-0xFF, inclusive. The 0x00-0x7F range is
 reserved for kernel use, and 0x80-0xFF is available for arbitrary use.

include/defines.inc

@@ -42,14 +42,15 @@ panic_failed_init       .equ 4
 
 ; KEXC headers
 ; 0x00-0x7F reserved for kernel use
-; 0x80-0xFF available for arbituary use
+; 0x80-0xFF available for arbitrary use
 KEXC_HEADER_END         .equ 0x00
 KEXC_ENTRY_POINT        .equ 0x01
 KEXC_STACK_SIZE         .equ 0x02
 KEXC_KERNEL_VER         .equ 0x03
 KEXC_THREAD_FLAGS       .equ 0x04
 KEXC_NAME               .equ 0x05
 KEXC_DESCRIPTION        .equ 0x06
+KEXC_RELOCATION_TABLE   .equ 0x07
 
 ; Thread flags
 THREAD_NON_SUSPENDABLE  .equ 2

src/00/thread.asm

@@ -354,6 +354,7 @@ _:  pop af
     cp a
     ret
 
+.echo "lp: 0x{0:X4}" launchProgram
 ;; launchProgram [Threading]
 ;;  Loads the specified file into memory as a program and starts a
 ;;  new thread for it. The file must be a valid KEXC executable.
@@ -426,12 +427,18 @@ launchProgram:
 .unknown_ver:
 ; no minimum version is specified by the executable
 .no_minimum_ver:
+; Check for a relocation table
+        ld b, KEXC_RELOCATION_TABLE
+        push ix \ call _getThreadHeader \ pop ix
+        call z, .relocate
+
         ; Grab header info
         ld b, KEXC_ENTRY_POINT
         push ix \ call _getThreadHeader \ pop ix
         jr nz, .no_entry_point
         push hl
-            ld b, KEXC_STACK_SIZE
+            ; b still has KEXC_ENTRY_POINT, and KEXC_STACK_SIZE is 1 higher
+            inc b
             push ix \ call _getThreadHeader \ pop ix
             ld c, l ; TODO: Error out if H is nonzero?
             jr z, _
@@ -459,14 +466,14 @@ _:  ld a, b
     pop bc
     cp a
     ret
-.kernel_too_low:
-    ld a, errKernelMismatch
+.magic_error:
+    ld a, errNoMagic
     jr .error
 .no_entry_point:
     ld a, errNoEntryPoint
     jr .error
-.magic_error:
-    ld a, errNoMagic
+.kernel_too_low:
+    ld a, errKernelMismatch
     jr .error
 .error_pop2:
     inc sp \ inc sp
@@ -484,6 +491,42 @@ _:  or 1
     ld a, b
     pop bc
     ret
+; thrashes de, bc, and hl
+.relocate:
+; ix = executable address
+; hl = program-relative relocation table address
+    push ix \ pop de
+    add hl, de
+; hl = absolute address of relocation table
+.relocation_loop:
+    ld e, (hl)
+    inc hl
+    ld d, (hl)
+    ; de = first entry in relocation table
+    dec hl
+    ; hl: preserved
+    ld bc, 0
+    call cpBCDE
+    ret z
+    ; de contains the program-relative address of a program-relative pointer to relocate
+    ; need to execute, in effect, `add (ix + de), ix`
+    push ix
+        add ix, de
+        push ix \ pop de
+    pop ix
+    ; de = absolute address of pointer to relocate
+   
+    ; add (de), ix
+    push ix \ pop bc
+    ld a, (de)
+    add a, c
+    ld (de), a
+    inc de
+    ld a, (de)
+    add a, b
+    ld (de), a
+    inc hl \ inc hl
+    jr .relocation_loop
 
 ;; exitThread [Threading]
 ;;  Immediately terminates the running thread.