Demo 15 Problem

[Andyhhp]

Did you make any changes to the code at all?

The optimiser can take the smallest change in source code into a huge change in terms of machine code

~Andrew

[Insightsoft]

No. Only this 3 line of NOP... just to find a way to freeze at this precisely location...
(And, this simple change was a reaction to the problem)

[Mike]

Hm, there is a couple of interesting things:

-You are using the floppy programming chapter. For simplicity purposes, please test with the keyboard chapters demo.
-Both of the above were built within Visual C++ 2008, so no upgrades of the project should be needed. What version of Visual C++ are you using?

[Insightsoft]

Oops, is asking me for the upgrade...
...and on the first compilation (just after the upgrade) it works fine
...then, on second compilation, and without any change, it crash!!!

I'm using the Visual Studio 2008 with Visual C++ 2008 Professional Edition...

[Mike]

Hello,

Please see my above post. Do you have the same problem with the keyboard programming chapters' demo? What happens when you Clean+Rebuild the project? Also, please post your compiler and linker command line switches please.

[XV8]

I use bochs. When keyboard interrupt occured bochs crash.
I set for all interrupts one default IR. It do nothing.
When i use in asm :

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asm("int $0")

bochs crash too.
Where mistake? May be that IDT Register have wrong value?
How i check it?

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#define MAX_INTERRUPTS		256
#define IDT_DESC_TYPE_INT_GATE 	 	 0x0E    //00001110
#define IDT_DESC_TYPE_TASK_GATE		 0x05    //00000101
#define IDT_DESC_TYPE_TRAP_GATE		 0x0F    //00001111
#define IDT_DESC_RING_0			 0x00    //00000000
#define IDT_DESC_RING_1			 0x20	 //00100000
#define IDT_DESC_RING_2		 	 0x40	 //01000000
#define IDT_DESC_RING_3		 	 0x60	 //01100000
#define IDT_DESC_PRESENT		 	 0x80	 //10000000




typedef void (*IRQ_HANDLER)(void);


struct IDTDescriptor
{
	
	unsigned short		Offset1;
	unsigned short		Selector;
	unsigned char		Reserved;
	unsigned char		Flags;
	unsigned short		Offset2;
};

struct IDTRegister
{
	unsigned short	Limit;
           unsigned int	Base;
};

static IDTDescriptor IDT[MAX_INTERRUPTS];
static IDTRegister   IDTR;

class iIDTManager
{
  public :
   int InstallIR(unsigned int, unsigned short, unsigned short, void (*func) ());
   int Init(unsigned short);
   IDTDescriptor* GetIR(unsigned int);
   void Install();
   iMemory MM;
 };

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#include "IDTManager.hpp"

void iIDTManager :: Install ()
{
asm("lidt (,%0,)"::"a" (&IDTR) );
}

void DefaultIR ()
{
	for(;;);
}

IDTDescriptor* iIDTManager ::  GetIR (unsigned int IRNum)
{
	if (IRNum>MAX_INTERRUPTS)
		return 0;
	return &IDT[IRNum];
}

int iIDTManager :: InstallIR (unsigned int IRNum, unsigned short Flags, unsigned short Selector, IRQ_HANDLER IRQ)
{

	if (IRNum>MAX_INTERRUPTS)
		return 0;

	if (!IRQ)
		return 0;

	unsigned long long		Base = (unsigned long long)&(*IRQ);
	IDT[IRNum].Offset1		=	(unsigned short)(Base & 0xffff);
	IDT[IRNum].Offset2		=	(unsigned short)((Base >> 16) & 0xffff);

	IDT[IRNum].Reserved		=	0;
	IDT[IRNum].Flags		=	(unsigned char) Flags;
	IDT[IRNum].Selector			=	Selector;

	return	0;
}

int iIDTManager :: Init (unsigned short CodeSelector)
{
	IDTR.Limit = sizeof (struct IDTDescriptor) * MAX_INTERRUPTS -1;
	IDTR.Base  = (unsigned int)&IDT[0];

	MM.SetBytes ((void*)&IDT[0], 0, sizeof (IDTDescriptor) * MAX_INTERRUPTS-1);
	for (int i=0; i<MAX_INTERRUPTS; i++)
		InstallIR (i, IDT_DESC_TYPE_INT_GATE | IDT_DESC_RING_0 | IDT_DESC_PRESENT,
			CodeSelector, (IRQ_HANDLER) DefaultIR);
	Install ();
	return 0;
}

[XV8]

i check the GDT register by sgdt instructions. But i got a wrong result.
Value which i got from GDT register is not valid. it different from value which i Load into them.
Limit of GDT is correct, But address of GDT in GDT register is wrong. I check it and i have found that it is 16 low bit of original value.

For Load to GDTR i use

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asm("lgdt (,%0,)"::"a" (&GDTRegStruct1))

for get GDTR value i use

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asm("sgdt (,%0,)"::"a" (&GDTRegStruct2))

where GDTRegStruct1 (2)

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struct GDTR
{
  unsigned short Limit;
  unsigned int Base;
} 

GDTR GDTRegStruct2,GDTRegStruct1;

also IDT register Load and Read has this problem.
i think that bochs crash because of this problem.


whats problem?
I do not know that to do.

[XV8]

Problem is resolved.
GCC align structure by size of the biggest field.

this is example

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struct test_t
{
  int  a;
  char b;
  int  c;
} ;

struct test_t test = { 10, 20, 30};

GCC compilier it to

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test:
	.long	10
	.byte	20
	.zero	3
	.long	30

GCC use .zero 3 for alignment.

If use directive __attribute__ ((packed)) GCC ignores alignment
for example

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struct test_t
{
  int  a;
  char b;
  int  c;
} __attribute__ ((packed));

struct test_t test = { 10, 20, 30};

And the object file

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test:
	.long	10
	.byte	20
	.long	30

[Andyhhp]

ahh. I forgot about alignment problems

a better method is to use "__attribute__((packet))" which will ensure that no padding happens

~Andrew

[Fanael]

ahh. I forgot about alignment problems

a better method is to use "__attribute__((packet))" which will ensure that no padding happens

~Andrew

Isn't it "__attribute__((packed))"?

[Andyhhp]

Yes it is - i cant spell