DOS 3.30 source code leak
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DOCUMENTATION FOR MS-DOS 3.30 BUGFIX DISKETTE
This diskette contains code for bugfixes in the MS-DOS 3.30 Release thatare corrected in the Microsoft MS-DOS 3.30 Packaged Product. These may alsobe corrected in an OEM's 3.30 product by utilizing the code on this diskette.To to this, just copy the files on this disk over the corresponding files inthe DISTRIBUTION DISKETTE tree before doing the builds and making up yourOEM product.
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Problem: FDISK: logical drive creation doesn't show on fdisk.
Run FDISK. Create a primary partition and then an extended partition. While creating the extended partition the menu sequence to create logical drives in the extended partition should turn up, but it doesn't.
Solution: Difference in versions of the C compiler (we used C 4.0 instead of C 3.0) exposed a bug in the forcing of a constant to a long unsigned number. The two compilers treat this differently.
Changes made were: a) FDISK.H : line 14 DOS_MAX = 64*1024 ....old DOS_MAX = 65536L ....new b) INT13.C : (not related to problem, was just something noticed along the way) line 148 max_head[0] ...old max_head[i] ...new
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MS-DOS 3.30 Beta FORMAT d: /S on very small partitions problem
Description: Attempting to do a FORMAT d: /S on a hard disk partition that is smaller than the space required for the system files resulted in the system files overwritting other partitions and format reporting approximately 4 GB of free space.
Problem: The problem is simply that a check is never done to see if enough free space exists to load the system files after the formatting is done. This problem also occurs on PC-DOS 3.30.
Solution: The solution is to add a check to make sure that there is enough free space for the system files before we attempt to copy them. This was done by adding a routine called CHKSPACE which is called just before WRITEDOS in the module FORMAT.ASM. CHKSPACE uses DOS interrupt Get Disk Free Space and compares the number of available clusters with the number required for the system files. If the amount of free space is greater than or equal to the amount of space required by the system files, CHKSPACE returns with the carry flag clear. Otherwise, it returns withe the carry flag set. Following the call to CHKSPACE is a check for carry. If carry is set, the message "No room for system on destination disk" is printed and the system files are not copied. If carry is not set, control continues on to WRITEDOS.
Modules: Fixing this bug required changing FORMAT.ASM, MESSAGES.ASM, and MESSAGES.INC.
Documentation: The entry for "No room for system on destination disk" in the messages section of the DOS manual states that this error message is the result of a SYS command. This should be changed to read SYS or FORMAT. In addition, the entry assumes that the destination disk is always a diskette and suggests that the appropriate action is to format a blank diskette with the /S option. This will do you no good if you are trying to add the system files to a hard disk partition. The recommended action should include using FDISK to make the partition larger and retrying the command if the error occured while attempting to format a hard disk partition with the /S option.
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Problem: Volumes in abundance cause boot problems.
Create primary partition and then the extended partition. in the extended partition create the maximum number of volumes permitted, i.e. 23. Try booting machine off a 3.30 floppy the machine is down on its knees. Problem doesn't exist if you have volumes < 23. Problem only on 6M AT.
Solution: MSBIO2 has a buffer of 23 BDSMs at the end. MSBIO2 is followed by MSHARD. Since the BDSMs are substancially long in size the bios relocates MSHARD to the paragraph boundary after the last BDSM used. This works fine for volumes < 23. However if all 23 BDSMs are used up MSHARD is relocated to the next para boundary which happens to be within MSHARD itself. So MSHARD ends up destroying itself.
Fix - a para buffer between the last BDSM and MSHARD in MSBIO2.ASM.
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Problem:
On exercising last two sysinit error messages dos code is displayed instead of just the messages.
Solution:
In calculating the location where to load dos, a constant is used to indicate the size of the sysinit segment. this is different for us.
Changes: In msequ.inc changed sysize from 200 to 203.
Further changes planned: Change the sysize constant to a variable sizing the sysinit segment.
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Problem: type filename > "=" hangs the system.
Not only = in quotes but any delimitor causes problems.
This comes from a basic lack of consistency in the treatment of the role of the " character. In command line parsing anything between " ----- " is not interpreted. But in forming filenames a " is taken as a valid character. Once the '>' character is reached the parser begins forming the filename and takes " as the first character. The following = is taken as a delimitor and the filename ended. When the filename is formed the processing returns to the command line parsing main routine and sees the next ". After this it just moves anything that comes along till it meets the next quote and ends up destroying the stack.
Solution: changed filename parsing code to test for quote and decrement the number of quotes. File changed - tmisc1.asm
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Problem: DOS FDISK creates partition which overlaps Xenix partition.
Create bad track table (xenix) and then a xenix partition which occupies whole disk. then boot dos and create partiton asking it to use all of the space for dos. It just does that overlapping the partition over the xenix partition.
Problem: 3.3 fdisk was not handling the no space condition.
Solution:
added code to detect no space condition and report error on such a condition. files changed fdisk.c and space.c. also when dos tries to create primary partition with a space requested from the user added error message when there is no space.
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Problem:
The bug is that the routine make_partition had been checking for a free "slot" in the Master Boot Record and aborting the menu if there was none. This action is not desirable if the user wishes to create a Logical DOS volume in an existing Extended DOS Partition.
There are several circumstances where this problem becomes evident. Probably the most common problem would be experienced on a large hard disk with several DOS partitions defined on it (COMPAQ is not the only OEM to support multiple DOS partitions on a hard disk...).
Consider a disk with 4 DOS partitions defined on it and the user wants to delete ONE of the DOS partitions so that an Extended DOS partition may be defined. After doing this, the ext_create_partition routine allows the user to define logical DOS volumes.
The user decides that the Logical DOS Volumes he previously created are not satisfactory after having left FDISK, perhaps he had previously defined only one Logical DOS Volume and it did not use the entire Extended Partition.
This time FDISK will not allow the user to select the Create Logical Volume menu option because there are no free "slots" in the Master Boot Record although there may well be plenty of space within the Extended DOS partition.
NOTE: This problem also occurs with the OS/2 implementation of FDISK.
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Problem: Extend file handle count is broken.
Solution: The para calculation code in handle.asm to calculate the number of paragraphs needed is coded wrongly. For handle values less than a para away from the maximum this will cause a carry. The subsequent rotate by 4 should shift the carry in. IBM 3.3 doesn't use the appropriate rotate instruction.
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Problem: Disk info initialisation in extended volume wrongly done.
The problem involves creation of Logical DOS Volumes in an Extended DOS Partition. As you know, each Logical DOS Volume has a "dummy" Master Boot Record which is necessary to define the extent of its Logical Volume and to indicate the location of the next Logical Volume (if one exists). The "dummy" Master Boot Record for each Logical Volume (except the last one) contains an entry with a system indicator byte with the value of 5 - this is the pointer to the next volume. The END_HEAD number of this type 5 record is ONE greater than the greatest physical head number on the drive. This occurs because the entries in the "max_head" array are initialized to be one more than the greatest physical head number in the routine "get_disk_info()" in the file INT13.C for use in calculations. The routine "write_ext_boot_to_disk" in the file DISKOUT.C does not subtract one from the max_head value before placeing it into the extended boot record - which is what results in the "End_Head" field being wrong for the type 5 record. The line in "write_ext_boot_to_disk" where the subtraction should take place is shown below... /* End head */ boot_record[0x1D3] = max_head[disk];
Solution: As mentioned above the line given above should be boot_record[0x1d3] = max_head[disk] - 1;
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