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Full Discussion: Mmap source
Operating Systems BSD Mmap source Post 302858477 by dcicc on Monday 30th of September 2013 01:43:25 PM
Old 09-30-2013
Mmap source
I'm new to kernels and C, and I am tinkering around trying to understand OpenBSD's secure memory management. I'm stumped on a couple points.

I've read up on malloc() which was apparently modified years ago to allocate memory using mmap. First question, that would be this here, right?

Code:
map_pages(size_t pages)
{
struct pdinfo *pi, *spi;
struct pginfo **pd;
u_long pidx,lidx;
void *result, *tail;
u_long index;

pages <<=malloc_pageshift;
result = MMAP(pages + malloc_guard);

For the life of me, I can't track down source code for mmap(). I know that this is a kernel system call, but where is that source? In particular, I'm interested to see how mmap() now returns a randomized location in memory.
Last edited by Scott; 09-30-2013 at 05:26 PM.. Reason: Code tags
 

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LEARN ABOUT FREEBSD

casueword

CASU(9) 						   BSD Kernel Developer's Manual						   CASU(9)

NAME

     casueword, casueword32, casuword, casuword32 -- fetch, compare and store data from user-space

SYNOPSIS

     #include <sys/types.h>
     #include <sys/systm.h>

     int
     casueword(volatile u_long *base, u_long oldval, u_long *oldvalp, u_long newval);

     int
     casueword32(volatile uint32_t *base, uint32_t oldval, uint32_t *oldvalp, uint32_t newval);

     u_long
     casuword(volatile u_long *base, u_long oldval, u_long newval);

     uint32_t
     casuword32(volatile uint32_t *base, uint32_t oldval, uint32_t newval);

DESCRIPTION

     The casueword functions are designed to perform atomic compare-and-swap operation on the value in the usermode memory of the current process.

     The casueword routines reads the value from user memory with address base, and compare the value read with oldval.  If the values are equal,
     newval is written to the *base.  In case of casueword32() and casueword(), old value is stored into the (kernel-mode) variable pointed by
     *oldvalp.	The userspace value must be naturally aligned.

     The callers of casuword() and casuword32() functions cannot distinguish between -1 read from userspace and function failure.

RETURN VALUES

     The casuword() and casuword32() functions return the data fetched or -1 on failure.  The casueword() and casueword32() functions return 0 on
     success and -1 on failure.

SEE ALSO

     atomic(9), fetch(9), store(9)

BSD
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