2011/6/15 Jeremy Chadwick <[email protected]>: > On Wed, Jun 15, 2011 at 03:57:05PM +0200, Joerg Wunsch wrote: >> When trying to use doscmd on 8-stable, all I get is: >> >> Error mapping HMA, HMA disabled: : Invalid argument >> Segmentation fault (core dumped) >> >> The segfault happens at the end of mem_init(), when the allocated DOS >> memory (which is located at virtual address 0) is attempted to be >> written to. Apparently, the mmap() failure that causes the "HMA >> disabled" message is actually a fatal error rather than a benign one >> the could be ignored, as it results in no valid DOS memory allocation >> at all. >> >> Right now, the only older system I could test it against uses FreeBSD >> 5.x, where the mmap() works as expected. So does anyone have an idea >> why this mmap() call: >> >> if (mmap((caddr_t)0x000000, 0x100000, >> PROT_EXEC | PROT_READ | PROT_WRITE, >> MAP_ANON | MAP_FIXED | MAP_SHARED, >> -1, 0) == MAP_FAILED) { >> perror("Error mapping HMA, HMA disabled: "); >> HMA_a20 = -1; >> close(HMA_fd_off); >> close(HMA_fd_on); >> return; >> } >> >> yields an EINVAL now under 8-stable?
As I remember, mapping of "zero" page forbidden by default. > I imagine that the page size ordeal is probably what's biting you. Now, > I'm not sure if page size in that above context refers to "kernel page > size" (e.g. hw.pagesizes or hw.pagesize) or if it refers to "a page of > memory" as in what libc/malloc uses. It refers. mmap(2) is system call. On i386/amd64 "big" page size is 2MB, and code above is trying to allocate 1MB, so memory will be allocated with 4KB-sized pages. > > I'm not sure why a person would need or want MAP_FIXED in this > situation; why can't they just take the result of mmap() (a void *) and > use that as a base address offset instead of assuming zero in their > software? AFAIK, doscmd is trying to emulate real mode on real hardware while being in protected mode, thus it want first pages of memory. Another way to do the same thing - open /dev/mem and call mmap() at zero offset. _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "[email protected]"
