-/* -----------------------------------------------------------------------------
- The mmap() method
-
- On Unix-like systems, we use mmap() to allocate our memory. We
- want memory in chunks of MBLOCK_SIZE, and aligned on an MBLOCK_SIZE
- boundary. The mmap() interface doesn't give us this level of
- control, so we have to use some heuristics.
-
- In the general case, if we want a block of n megablocks, then we
- allocate n+1 and trim off the slop from either side (using
- munmap()) to get an aligned chunk of size n. However, the next
- time we'll try to allocate directly after the previously allocated
- chunk, on the grounds that this is aligned and likely to be free.
- If it turns out that we were wrong, we have to munmap() and try
- again using the general method.
-
- Note on posix_memalign(): this interface is available on recent
- systems and appears to provide exactly what we want. However, it
- turns out not to be as good as our mmap() implementation, because
- it wastes extra space (using double the address space, in a test on
- x86_64/Linux). The problem seems to be that posix_memalign()
- returns memory that can be free()'d, so the library must store
- extra information along with the allocated block, thus messing up
- the alignment. Hence, we don't use posix_memalign() for now.
-
- -------------------------------------------------------------------------- */
-
-#if !defined(mingw32_HOST_OS) && !defined(cygwin32_HOST_OS)
-
-// A wrapper around mmap(), to abstract away from OS differences in
-// the mmap() interface.
-
-static void *
-my_mmap (void *addr, lnat size)
-{
- void *ret;
-
-#if defined(solaris2_HOST_OS) || defined(irix_HOST_OS)
- {
- int fd = open("/dev/zero",O_RDONLY);
- ret = mmap(addr, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
- close(fd);
- }
-#elif hpux_HOST_OS
- ret = mmap(addr, size, PROT_READ | PROT_WRITE,
- MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
-#elif darwin_HOST_OS
- // Without MAP_FIXED, Apple's mmap ignores addr.
- // With MAP_FIXED, it overwrites already mapped regions, whic
- // mmap(0, ... MAP_FIXED ...) is worst of all: It unmaps the program text
- // and replaces it with zeroes, causing instant death.
- // This behaviour seems to be conformant with IEEE Std 1003.1-2001.
- // Let's just use the underlying Mach Microkernel calls directly,
- // they're much nicer.
-
- kern_return_t err;
- ret = addr;
- if(addr) // try to allocate at adress
- err = vm_allocate(mach_task_self(),(vm_address_t*) &ret, size, FALSE);
- if(!addr || err) // try to allocate anywhere
- err = vm_allocate(mach_task_self(),(vm_address_t*) &ret, size, TRUE);
-
- if(err) {
- // don't know what the error codes mean exactly, assume it's
- // not our problem though.
- errorBelch("memory allocation failed (requested %lu bytes)", size);
- stg_exit(EXIT_FAILURE);
- } else {
- vm_protect(mach_task_self(),(vm_address_t)ret,size,FALSE,VM_PROT_READ|VM_PROT_WRITE);
- }
-#else
- ret = mmap(addr, size, PROT_READ | PROT_WRITE | PROT_EXEC,
- MAP_ANON | MAP_PRIVATE, -1, 0);
-#endif
-
- if (ret == (void *)-1) {
- if (errno == ENOMEM ||
- (errno == EINVAL && sizeof(void*)==4 && size >= 0xc0000000)) {
- // If we request more than 3Gig, then we get EINVAL
- // instead of ENOMEM (at least on Linux).
- errorBelch("out of memory (requested %lu bytes)", size);
- stg_exit(EXIT_FAILURE);
- } else {
- barf("getMBlock: mmap: %s", strerror(errno));
- }
- }
-
- return ret;
-}
-
-// Implements the general case: allocate a chunk of memory of 'size'
-// mblocks.
-
-static void *
-gen_map_mblocks (lnat size)
-{
- int slop;
- void *ret;
-
- // Try to map a larger block, and take the aligned portion from
- // it (unmap the rest).
- size += MBLOCK_SIZE;
- ret = my_mmap(0, size);
-
- // unmap the slop bits around the chunk we allocated
- slop = (W_)ret & MBLOCK_MASK;
-
- if (munmap(ret, MBLOCK_SIZE - slop) == -1) {
- barf("gen_map_mblocks: munmap failed");
- }
- if (slop > 0 && munmap(ret+size-slop, slop) == -1) {
- barf("gen_map_mblocks: munmap failed");
- }
-
- // ToDo: if we happened to get an aligned block, then don't
- // unmap the excess, just use it. For this to work, you
- // need to keep in mind the following:
- // * Calling my_mmap() with an 'addr' arg pointing to
- // already my_mmap()ed space is OK and won't fail.
- // * If my_mmap() can't satisfy the request at the
- // given 'next_request' address in getMBlocks(), that
- // you unmap the extra mblock mmap()ed here (or simply
- // satisfy yourself that the slop introduced isn't worth
- // salvaging.)
- //
-
- // next time, try after the block we just got.
- ret += MBLOCK_SIZE - slop;
- return ret;
-}
-
-