Using the Bochs image the entry values for os2ldr are:
eax: 0x00000000 ecx: 0x00000000 edx: 0x00001480 ebx: 0x00000000 esp: 0x00005000 ebp: 0x00000000 esi: 0xFFFF000B edi: 0x0000124A eip: 0x00000000 eflags 0x00000246 IOPL=0 id vip vif ac vm rf nt of df IF tf sf ZF af PF cf cs:s=0x1000, dl=0x0000ffff, dh=0x00009b01, valid=1 ds:s=0x8800, dl=0x8000ffff, dh=0x00009308, valid=7 ss:s=0x8800, dl=0x8000ffff, dh=0x00009308, valid=7 es:s=0x8800, dl=0x8000ffff, dh=0x00009308, valid=1 fs:s=0x3000, dl=0x0000ffff, dh=0x00009303, valid=7 gs:s=0x0000, dl=0x0000ffff, dh=0x00009300, valid=1 ldtr:s=0x0000, dl=0x0000ffff, dh=0x00008200, valid=1 tr:s=0x0000, dl=0x0000ffff, dh=0x00008300, valid=1 gdtr:base=0x000faeb2, limit=0x30 idtr:base=0x00000000, limit=0x3ff
DH boot mode flags:
- bit 0 (NOVOLIO) on indicates that the mini-FSD does not use MFSH_DOVOLIO.
- bit 1 (RIPL) on indicates that boot volume is not local (RIPL boot)
- bit 2 (MINIFSD) on indicates that a mini-FSD is present.
- bit 3 (RESERVED)
- bit 4 (MICROFSD) on indicates that a micro-FSD is present.
- bits 5-7 are reserved and MUST be zero.
DL drive number for the boot disk. This parameter is ignored if either the NOVOLIO or MINIFSD bits are zero.
DS:SI is a pointer to the BOOT Media’s BPB. This parameter is ignored if either the NOVOLIO or MINIFSD bits are zero.
ES:DI is a pointer to a filetable structure.
The filetable structure has the following format:
struct FileTable {
unsigned short ft_cfiles; /* # of entries in this table */
unsigned short ft_ldrseg; /* paragraph # where OS2LDR is loaded */
unsigned long ft_ldrlen; /* length of OS2LDR in bytes */
unsigned short ft_museg; /* paragraph # where microFSD is loaded */
unsigned long ft_mulen; /* length of microFSD in bytes */
unsigned short ft_mfsseg; /* paragraph # where miniFSD is loaded */
unsigned long ft_mfslen; /* length of miniFSD in bytes */
unsigned short ft_ripseg; /* paragraph # where RIPL data is loaded */
unsigned long ft_riplen; /* length of RIPL data in bytes */
/* The next four elements are 16:16 pointers to microFSD entry points */
unsigned short (far *ft_muOpen) (char far *pName, unsigned long far *pulFileSize);
unsigned long (far *ft_muRead) (long loffseek, char far *pBuf, unsigned long cbBuf);
unsigned long (far *ft_muClose)(void);
unsigned long (far *ft_muTerminate)(void);
}
Bochs values:
| filetable structure | value |
| ft_cfiles | 0x0003 |
| ft_ldrseg | 0x1000 |
| ft_ldrlen | 0x0000A800 |
| ft_museg | 0x8800 |
| ft_mulen | 0x00005000 |
| ft_mfsseg | 0x007C |
| ft_mfslen | 0x0000EAE9 |
| ft_ripseg | 0x0000 |
| ft_riplen | 0x00000000 |
| ft_muOpen | 8800:1A9C |
| ft_muRead | 8800:1BD4 |
| ft_muClose | 8800:1DAE |
| ft_muTerminate | 8800:1DD4 |
The microFSD entry points interface is defined as follows:
mu_Open – is passed a far pointer to name of file to be opened and a far pointer to a ULONG to return the file’s size. The returned value (in AX) indicates success(0) or failure(non-0).
mu_Read – is passed a seek offset, a far pointer to a data buffer, and the size of the data buffer. The returned value(in DX:AX) indicates the number of bytes actually read.
mu_Close – has no parameters and expects no return value. It is a signal to the micro-FSD that the loader is done reading the current file.
mu_Terminate – has no parameters and expects no return value. It is a signal to the micro-FSD that the loader has finished reading the boot drive.
The loader will call the micro-FSD in a Open-Read-Read-….-Read-Close sequence with each file read in from the boot drive.