OSDev.org

struct BIOSInfo
{
BYTE MajorVersion;
BYTE MinorVersion;
};

BIOSInfo *BIOS_Info_Pointer = 0;

error: 'BIOSInfo' undeclared (first use in this function)
error: (Each undeclared identifier is reported only once
error: for each function it appears in.)
error: Parse error before "BIOS_Info_Pointer"

Googles wrote: I have defined a structure:

Code: Select all

struct BIOSInfo
{
BYTE MajorVersion;
BYTE MinorVersion;
};

And when I'm trying to use it...

Code: Select all

BIOSInfo *BIOS_Info_Pointer = 0;

...GCC replies:

error: 'BIOSInfo' undeclared (first use in this function)
error: (Each undeclared identifier is reported only once
error: for each function it appears in.)
error: Parse error before "BIOS_Info_Pointer"

What is GCC trying to say?

typedef struct X {
...
} X;

Googles wrote:
ld complains about not finding the reference to "_Get_ASM_Params". For some reason ld doesn't complain when I'm using "extern BIOSInfo Get_ASM_Params(void);"?

AR wrote: The reasons that first come to mind are; ASM is harder to read later and lacks the ability to structure it easily and you have to write a lot of operators for something that you would think is simple, for example:

Code: Select all

unsigned int MyVar = (0xFF << 8) * 6 + 9;

Code: Select all

push eax
mov eax, 0xFF
shl eax, 8
mul eax, 6
add eax, 9
mov [MyVar], eax
pop eax

[SECTION .bss]
MyVar: resd 1

C has pretty much the same concepts as ASM though, like a pointer is an address which you can dereference, in Intel ASM you dereference with [ ] where in C it's *.

unsigned int MyVar = (0xFF << 8) * 6 + 9;

[SECTION .data]
MyVar dd 0FFh * 256 * 6 + 9

while(obj && !obj->done) {
    x
}

n_wh:
mov eax, [obj]
cmp eax, 0
je end_wh
mov ebx, [eax+done_offs]
cmp ebx, 0
je end_wh
x;
jmp n_wh
end_wh: