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Old 10-22-2009, 09:24 PM   #1
raghu2383
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Registered: Jun 2008
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Find Physical address of memory provided by kmalloc


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.
 
Old 10-22-2009, 10:28 PM   #2
smeezekitty
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Registered: Sep 2009
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Distribution: M$ Windows / Debian / Ubuntu / DSL / many others
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Quote:
Originally Posted by raghu2383 View Post
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
 
Old 10-23-2009, 02:07 PM   #3
raghu2383
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Registered: Jun 2008
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CS is the code segment right? If I am right would that give me the location of where the executable code is loaded?
 
Old 10-23-2009, 02:25 PM   #4
smeezekitty
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Quote:
Originally Posted by raghu2383 View Post
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.
 
  


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