Getting VESA video information with Digital Mars compiler, which doesn't support GNU C packed structs

Question

I'm trying to add VESA video card detection to my system information program and can't seem to even put together code that works. I've looked at this thread: How to get VESA BIOS Information and this page on OSDev: https://wiki.osdev.org/VESA_Video_Modes which has code using __attribute__ ((packed)) written for the gcc compiler that's incompatible with my Digital Mars compiler.

All I really want is the VESA Version, OEMString, Total Memory, and if VESA 2.0 is supported, the OEMModel string, but if I have to process the entire ES:DI stack to get that information, so be it. However, that's where I'm stuck. I simply don't know how to grab that information and put it into a structure despite the example code given.

I know this site isn't for writing code for the questioner, but I'm hoping someone can help get me started so I can study working code and learn how to accomplish this. I don't care if it's in assembly or C++, though I have a tad more experience with C++.

I'm using the MARS C/C++ compiler. The generated programs will be 16-bit DOS programs.

Answer 1

I was able to get all related VESA information using the following code, no PACKing needed:

typedef struct _VBE_INFO
{
    char VbeSignature[4];
    uint16 VbeVersion;
    char FAR *fpOemString;
    uint32 Capabilities;
    uint16 FAR *fVideoMode;
    uint16 TotalMemory;
    /* VESA 2.x */
    uint16 OemSoftwareRev
    char FAR *fpOemVendorName;
    char FAR *fpOemProductName;
    char FAR *fpOemProductRev;
    char Reserved[222];
    char OemData[256];
} VBE_INFO;

VBE_INFO FAR *VbeInfo;
inregs.x.ax = 0x4F00;
sregs.es    = FP_SEG( VbeInfo );
inregs.x.di = FP_OFF( VbeInfo ):
int86x( 0x10, &inregs, &outregs, &sregs );

Then all your data is sitting in VbeInfo->? where ? is defined in the structure. E.g. VbeInfo->fpOemString contains the VESA v1.x Oem String data for the card. For VESA 2.x information, use the following code:

VBE_INFO FAR *VbeInfo;
_fstrncpy( VbeInfo->VbeSignature, "VBE2", 4 );
inregs.x.ax = 0x4F00;
sregs.es    = FP_SEG( VbeInfo );
inregs.x.di = FP_OFF( VbeInfo );
int86x( 0x10, &inregs, &outregs, &sregs );

Then information below the VESA 2.x comment in the struct will be populated.