Malloc implementation in C Post: 302399396

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Top Forums Programming Malloc implementation in C Post 302399396 by Gambit_b on Saturday 27th of February 2010 08:00:02 PM

02-27-2010

Registered User

Malloc implementation in C

Hey Guys

I am trying to implement the malloc function for my OS class and I am having a little trouble with it. I would be really grateful if I could get some hints on this problem.
So I am using a doubly-linked list as my data structure and I have to allocate memory for it (duh...). The problem is that I am not allowed to use malloc for this(which makes sense because I am implementing one. I laugh really hard when people use malloc in their own implemented malloc replacement; belive me I have seen them). Anyways so ya I am confused as to how could you do this. I was thinking of mmap() but that can't work as it requires a file descriptor, moreover I can only call it just once so I have no idea how to do this.
Any help will be greatly appreciated

---------- Post updated at 06:52 PM ---------- Previous update was at 06:51 PM ----------

Now i noe i am not supposed to ask hw problems but I am really confused and I just want hints. My professor is out of town and he will be back later. So i am just worried how can I do this.
Please help guys, any hints???????

---------- Post updated at 07:00 PM ---------- Previous update was at 06:52 PM ----------

Oh I forgot to mention. I am getting memory from OS using mmap and this is the code till now

int fd = open("/dev/zero", O_RDWR);

// sizeOfRegion (in bytes) needs to be evenly divisible by the page size
void *ptr = mmap(NULL, sizeOfRegion,
PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);

I need to allocate memory for my list in this memory. Thanks

Gambit_b

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LEARN ABOUT BSD

falloc

MALLOC(3F)																MALLOC(3F)

NAME

       malloc, free, falloc - memory allocator

SYNOPSIS

       subroutine malloc (size, addr)
       integer size, addr

       subroutine free (addr)
       integer addr

       subroutine falloc (nelem, elsize, clean, basevec, addr, offset)
       integer nelem, elsize, clean, addr, offset

DESCRIPTION

       Malloc, falloc  and  free  provide  a general-purpose memory allocation package.  Malloc returns in addr the address of a block of at least
       size bytes beginning on an even-byte boundary.

       Falloc allocates space for an array of nelem elements of size elsize and returns the address of the block in addr.  It zeros the  block	if
       clean  is  1.  It returns in offset an index such that the storage may be addressed as basevec(offset+1) ... basevec(offset+nelem).  Falloc
       gets extra bytes so that after address arithmetic, all the objects so addressed are within the block.

       The argument to free is the address of a block previously allocated by malloc or falloc; this space is made available for  further  alloca-
       tion, but its contents are left undisturbed.  To free blocks allocated by falloc, use addr in calls to free, do not use basevec(offset+1).

       Needless to say, grave disorder will result if the space assigned by mallocorfalloc is overrun or if some random number is handed to free.

DIAGNOSTICS

       Malloc and falloc set addr to 0 if there is no available memory or if the arena has been detectably corrupted by storing outside the bounds
       of a block.

       The following example shows how to obtain memory and use it within a subprogram:

	     integer addr, work(1), offset
		...
	     call falloc ( n, 4, 0, work, addr, offset )
	     do 10 i = 1, n
	     work(offset+i) = ...
       10    continue

       The next example reads in dimension information, allocates space for two arrays and two vectors, and calls subroutine doit to do the compu-
       tations:

	     integer addr, dummy(1), offs
	     read *, k, l, m
	     indm1   = 1
	     indm2   = indm1 + k*l
	     indm3   = indm2 + l*m
	     indsym  = indm3 + k*m
	     lsym = n*(n+1)/2
	     indv  = indsym + lsym
	     indtot = indv + m
	     call falloc ( indtot, 4, 0, dummy, addr, offs )
	     call doit( dummy(indm1+offs), dummy(indm2+offs),
	    .		dummy(indm3+offs), dummy(indsym+offs),
	    .		dummy(indv +offs), m, n, lsym )
	     end
	     subroutine doit( arr1, arr2, arr3, vsym, vec, m, n, lsym )
	     real arr1(k,l), arr2(l,m), arr3(k,m), vsym(lsym), v2(m)
		...

FILES

       /usr/lib/libU77.a

SEE ALSO

       malloc(3)

4.3 Berkeley Distribution					   May 15, 1985 							MALLOC(3F)