78 lines
2.3 KiB
C
78 lines
2.3 KiB
C
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#include <stdlib.h>
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#include <stdio.h>
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#include <errno.h>
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#include <sys/mman.h>
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void *mmap(void *addr, size_t len, int prot, int flags, int fildes, off_t off) {
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/* man page for mmap says:
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* If addr is NULL, then the kernel chooses the (page-aligned) address at
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* which to create the mapping; this is the most portable method of creating a
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* new mapping.
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*
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* For our purpose (Solo5 & OCaml), OCaml might use a NULL addr and force us to
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* use posix_memalign.
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* OCaml calls mmap with a non-null address and with the MAP_FIXED flag only
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* on already reserved memory to commit or decommit that memory block, ie to
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* set its protection to PROT_READ|PROT_WRITE or to PROT_NONE, in the
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* caml_mem_commit and caml_mem_decommit functions.
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* So we accept this particular case without allocating memory that would leak
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* since the OCaml code base simply ignores the returned value (as MAP_FIXED
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* enforces the returned value to be either addr or MAP_FAILED).
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*
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* The OCaml runtime uses [mmap()] only to allocate memory, so only
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* [fildes == 1] is handled.
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*/
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(void)prot; // unused argument
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if (fildes != -1) {
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printf("mmap: file descriptor is unsupported.\n");
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abort();
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}
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if (!(flags & MAP_ANONYMOUS) || off != 0) {
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printf("mmap: only MAP_ANONYMOUS (and offset is 0) is supported.\n");
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abort();
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}
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void *ptr = NULL;
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if (addr == NULL) {
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/* posix_memalign doesn't modify ptr on error: ptr will still be NULL and
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* so we will return MAP_FAILED with no need to check explicitly the value
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* returned by posix_memalign */
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posix_memalign(&ptr, OCAML_SOLO5_PAGESIZE, len);
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} else {
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if ((flags & MAP_FIXED) != 0) {
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/* Case where mmap is called to commit or decommit already reserved
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* memory. Since we ignore prot, we can simply let it go through */
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return addr;
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} else {
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/* We cannot handle this case */
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errno = EINVAL;
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}
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}
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if (ptr == NULL) {
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return MAP_FAILED;
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} else {
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return ptr;
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}
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}
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int munmap(void *addr, size_t length)
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{
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(void)length; // unused argument
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/* man page for munmap says:
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* The address addr must be a multiple of the page size (but length need not be).
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*/
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if ((uintptr_t)addr & OCAML_SOLO5_PAGESIZE != 0) {
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errno = EINVAL;
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return -1;
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}
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free(addr);
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return 0;
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}
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