Changeset 43 for trunk/INCLUDE/ASM.INC

Timestamp:

Apr 11, 2014, 11:48:01 PM (11 years ago)

Author:

Ben Rietbroek

Message:

BSS Corruption Problem located (auxdebug on) [2012-02-21]

WARNING!!

All commits upto and including the commit of [2012-05-13] contain
a severe bug!! Building from these sources and then disabling
the 'force LBA' feature while also using the drive-letter feature or
editing the label can DESTROY THE MBR on ALL ATTACHED DISKS!!
DO NOT DISABLE 'FORCE LBA USAGE' WHEN BUILT FROM THE THESE COMMITS!!

Problem

o Function with Xrefs goes out-of-bounds because hideparttable is too small

Has only 30 entries and should be 45.
Lost partition checker initializes out-of-bounds.

Info

o About the hideparttable

For each partition it can be specified which other partitions need to
be hidden when that partition is booted. This is useful for legacy DOS
but also braindead Windows that presents HPFS/JFS partitions as
unformatted and tries to persuade the user to format them.
With v1.07 the numer of partitions that can be handled was expanded from
30 to 45, but the size of the hideparttable was overseen.

o The need to compress the hideparttable

The old size was 30x30=900 bytes while the required size is 45x45=2045 bytes.
This amount of space is not available in the image.
Since 6 bits are enough to identify the partition number to be hidden,
the solution is to devide the table into bitfields. This will result
in a table of (45*45*6)/8=1519 bytes, which can be fitted.

Changes

Revamped the sources quite a bit and moved the history to a separate
file. (AIR-BOOT.HIS)

New

o FIXCODE script for Linux

Just until the C version is ready...

File:

• trunk/INCLUDE/ASM.INC (modified) (1 diff)

trunk/INCLUDE/ASM.INC

@@ -35 +35 @@
 EndM
 
+
+;
+; An ORG directive resets the location counter where code and data is
+; generated. If the location counter is reset back to a point where
+; code or data already has been generated, this will be overwritten
+; without warning.
+; This macro can be used with every ORG directive to check for this condition,
+; and when it occurs further assembly is terminated.
+
+; NOTE:  Overlapchecking in JWasm is not as reliable as in Tasm.
+;        Because it's a single pass assembler, the current location can be
+;        incorrect. Tasm with multiple passes works correct.
+; FIXME: Get JWasm and Tasm use some common ECHO/%OUT method.
+;        (Tasm only pases first word of non-quoted string to a macro)
+check_overlap   MACRO   loc
+
+    ; Exit macro immediately if no overlap.
+    ; We don't want to assign values to z_last_... if there is no
+    ; overlap because they would then hold the values the last time this
+    ; macro was called and not those of the last overlap.
+    IF (loc - $) LE 0
+    ;~ IF ($ - loc) GE 0
+        EXITM
+    ENDIF
+
+    ; Calculate the overlap.
+    z_last_overlap_size = (loc - $)
+    z_last_overlap_location = loc - z_last_overlap_size
+
+    IFDEF   JWASM
+        ; Output message.
+        ECHO
+        ECHO ** ERROR: LOCATION OVERLAP DETECTED [JWASM] ! **
+        ECHO .         THIS IS MOST LIKELY CAUSED BY CODE / DATA
+        ECHO .         EXPANSION TOWARDS AN 'ORG' DIRECTIVE.
+        ECHO .         LOOK AT 'z_last_overlap_location' TO SEE WHERE.
+        ECHO .         LOOK AT 'z_last_overlap_size' TO SEE SIZE.
+        ECHO .         FORCING ERROR...
+        ECHO
+    ENDIF
+    IFDEF   TASM
+        IF2
+            ; Output message (only on pass2).
+            %OUT
+            %OUT ** ERROR: LOCATION OVERLAP DETECTED [TASM] ! **
+            %OUT .         THIS IS MOST LIKELY CAUSED BY CODE / DATA
+            %OUT .         EXPANSION TOWARDS AN 'ORG' DIRECTIVE.
+            %OUT .         LOOK AT 'z_last_overlap_location' TO WHERE.
+            %OUT .         LOOK AT 'z_last_overlap_size' TO SEE SIZE.
+            %OUT .         FORCING ERROR...
+            %OUT
+        ENDIF
+    ENDIF
+
+    ; Terminate assembly by forcing an error.
+    .ERR
+
+ENDM
+
+
 ; Shortcuts for pointer-types
 bptr                             equ   byte ptr