duskos

commit a680f1ecf8953f05f92d55ff0b508fb79dd03c5b
parent ee0beaf1bbed9779c107ea59d4ca605400dd4e56
Author: Virgil Dupras <hsoft@hardcoded.net>
Date:   Thu, 21 Jul 2022 19:51:42 -0400

asm/i386: improve modrm handling in 16bit mode

Also add LGDT and LIDT.

Diffstat:
M
fs/asm/i386.fs
 | 
23
+++++++++++++++++------

1 file changed, 17 insertions(+), 6 deletions(-)
diff --git a/fs/asm/i386.fs b/fs/asm/i386.fs
@@ -7,7 +7,6 @@
 4 const SP         5 const BP          6 const SI          7 const DI
 0 const AL         1 const CL          2 const DL          3 const BL
 4 const AH         5 const CH          6 const DH          7 const BH
-5 const MEM \ mod 0 + r/m 5 == abs memory
 4 const SIB \ mod 0/1/2 + r/m 4 == SIB
 
 0 value op8b    \ is current op in 8bit mode?
@@ -23,11 +22,13 @@
 
 \ Utilities
 : asm$ 0 to op8b 1 to opdirec 3 to opmod -1 to opreg -1 to oprm 0 to imm? ;
-: _err abort" argument error" ;
+: _err asm$ abort" argument error" ;
 : _assert not if _err then ;
 : w, here w! 2 allot ;
 : isbyte? ( n -- f ) $100 < ;
 : is16bit? realmode ;
+\ in 16bit, abs mem = mod0 + rm 6, in 32-bit, it's rm 5
+: memoprm 5 is16bit? + ;
 : dw, is16bit? if w, else , then ;
 : dwc, op8b if c, else dw, then ;
 
@@ -57,7 +58,7 @@
 
 : disp, ( -- ) \ write down displacement if needed.
   opmod case
-    0 of = oprm MEM = if disp dw, then endof
+    0 of = oprm memoprm = if disp dw, then endof
     1 of = disp c, endof
     2 of = disp dw, endof
   endcase ;
@@ -107,15 +108,24 @@ AL _ al   BL _ bl   CL _ cl   DL _ dl   AH _ ah   BH _ bh   CH _ ch   DH _ dh
 
 : i) ( imm -- ) 1 to imm? to imm ;
 
+: 16breg>[oprm] ( reg ) case
+    SI of = 4 endof
+    DI of = 5 endof
+    BP of = 6 endof
+    BX of = 7 endof
+    _err
+  endcase ;
+
 : d) ( disp -- ) to disp
   oprm 0< if \ first argument. we need to move it to oprm and change direction
     opreg to oprm
     -1 to opreg
     0 to opdirec
   then
+  is16bit? if oprm 16breg>[oprm] to oprm then
   oprm SP = if $24 to sib then \ special case for ESP
   disp case
-    of not oprm MEM = to opmod endof \ mod = 0 except if rm==MEM
+    of not oprm memoprm = to opmod endof \ mod = 0 except if rm==MEM
     of isbyte? 1 to opmod endof
     2 to opmod
   endcase ;
@@ -124,7 +134,7 @@ AL _ al   BL _ bl   CL _ cl   DL _ dl   AH _ ah   BH _ bh   CH _ ch   DH _ dh
   oprm 0< _assert \ can't have m) with second argument
   opreg 0< if \ first argument, we invert direction
     0 to opdirec then
-  0 to opmod MEM to oprm ;
+  0 to opmod memoprm to oprm ;
 
 \ Operations
 
@@ -161,7 +171,7 @@ $840f op jz,        $850f op jnz,
 $04e9 op jmp,      $02e8 op call,
 
 \ Single operand
-\ opcode format 00000000 00000rrr mmmmmmmm mmmmmm00
+\ opcode format 00000000 00000rrr mmmmmmmm mmmmmmmm
 \ r = opreg override
 \ m = modrm opcode
 : op ( reg opcode -- ) doer , does> @ ( opcode -- )
@@ -169,6 +179,7 @@ $04e9 op jmp,      $02e8 op call,
 $0400f7 op mul,    $0300f7 op neg,     $0200f7 op not,
 $0100ff op dec,    $0000ff op inc,
 $009f0f op setg,   $009c0f op setl,    $00940f op setz,    $00950f op setnz,
+$02010f op lgdt,   $03010f op lidt,
 
 \ Two operands
 \ opcode format 00000000 ssssssss iiiiirrr mmmmmm00