duskos

commit 42f38fc09b312c97c826d7706efceb4fae41263a
parent e12386d710b006bed11b9d221a3d21eb45a765f9
Author: Virgil Dupras <hsoft@hardcoded.net>
Date:   Tue,  6 Dec 2022 20:21:24 -0500

asm/i386: fix mis-assembling of some imm8 ops

Diffstat:
M
fs/asm/i386.fs
 | 
5
++++-
M
fs/tests/asm/i386.fs
 | 
7
+++++++

2 files changed, 11 insertions(+), 1 deletion(-)
diff --git a/fs/asm/i386.fs b/fs/asm/i386.fs
@@ -81,7 +81,10 @@
 
 : opimm, ( opcode opreg -- ) \ write the operation in "immediate" mode
   opreg! op8b not if
-    1 or imm isbyte? if ( sign-extended imm8 ) 8b! 2 or then then
+    \ TODO: for now, we stay on the safe side for the 8b optimization because
+    \ some ops have a sign-extended imm8 and some ops don't, but we could do
+    \ better.
+    1 or imm $80 < if ( sign-extended imm8 ) 8b! 2 or then then
   op, msd, imm, asm$ ;
 
 \ Setting arguments
diff --git a/fs/tests/asm/i386.fs b/fs/tests/asm/i386.fs
@@ -105,4 +105,11 @@ code foo9 ( n -- n )
 12 foo9 12 #eq
 42 foo9 43 #eq
 54 foo9 55 #eq
+
+\ the assembler used to mis-assemble ops with imm > $80 but < $100.
+code foo10 ( n -- n )
+    bp 0 d) $80 i) add,
+    ret,
+
+1 foo10 $81 #eq
 testend