[SOLVED] Find Physical address of memory provided by kmalloc

raghu2383 · 10-22-2009, 09:24 PM

Hi,

I allocated a chunk of memory using kmalloc in a Device Driver. Kmalloc provides a pointer to the allocated memory. This is one of my first few drivers, so please bear with me if my concepts are wrong.

I assume that the address returned is a Virtual address. I need to find the physical address of the memory location. I am working on an Intel 64 bit Fedora machine. I used the virt_to_phys() routine present in <asm/io_64.h>. I found that this routine returns an unsigned long value (32 bit) instead of an unsigned long long value (64 bit). Moreover, it seems that it simply returns the address - OFFSET instead of extracting the value in the page tables.

So is there any function / system call in Linux which will allow me to see the actual physical address on the Intel 64 arch.

Thanks for responding.

smeezekitty · 10-22-2009, 10:28 PM

Quote:

Originally Posted by raghu2383

Hi,

I allocated a chunk of memory using kmalloc in a Device Driver. Kmalloc provides a pointer to the allocated memory. This is one of my first few drivers, so please bear with me if my concepts are wrong.

I assume that the address returned is a Virtual address. I need to find the physical address of the memory location. I am working on an Intel 64 bit Fedora machine. I used the virt_to_phys() routine present in <asm/io_64.h>. I found that this routine returns an unsigned long value (32 bit) instead of an unsigned long long value (64 bit). Moreover, it seems that it simply returns the address - OFFSET instead of extracting the value in the page tables.

So is there any function / system call in Linux which will allow me to see the actual physical address on the Intel 64 arch.

Thanks for responding.

try :

Code:

struct address {
unsigned segment,offset;
};

address get_pointer_address(void *p){
address ret;
int i;
asm {
mov eax,cs
mov i,eax
}
ret.segment = i;
ret.offset = (unsigned)p;
return ret;
}

i am not sure if it will work

raghu2383 · 10-23-2009, 02:07 PM

CS is the code segment right? If I am right would that give me the location of where the executable code is loaded?

smeezekitty · 10-23-2009, 02:25 PM

Quote:

Originally Posted by raghu2383

CS is the code segment right? If I am right would that give me the location of where the executable code is loaded?

yes.
heres an example of how it might work:

Code:

struct address {
unsigned segment,offset;
};

address get_pointer_address(void *p){
address ret;
int i;
asm {
mov eax,cs
mov i,eax
}
ret.segment = i;
ret.offset = (unsigned)p;
return ret;
}
int main(){
void *p=kmalloc(10);
address x;
x = get_pointer_address(p);
printf("the address of the pointer is %u:%u", x.segment, x.offset);
kfree(p);
}

should work.