Date: Wed, 15 Jun 2011 17:46:42 +0300 From: nickolasbug@gmail.com To: Jeremy Chadwick <freebsd@jdc.parodius.com> Cc: freebsd-stable@freebsd.org, Joerg Wunsch <joerg@freebsd.org> Subject: Re: doscmd under 8-stable, anyone? Message-ID: <BANLkTinaw2AM6wBcJc4hUwLgQWmEwJfg7Q@mail.gmail.com> In-Reply-To: <20110615141240.GA61227@icarus.home.lan> References: <20110615135704.GQ23206@uriah.heep.sax.de> <20110615141240.GA61227@icarus.home.lan>
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2011/6/15 Jeremy Chadwick <freebsd@jdc.parodius.com>:
> 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. =A0Apparently, 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. =A0So does anyone have an idea
>> why this mmap() call:
>>
>> =A0 =A0 if (mmap((caddr_t)0x000000, 0x100000,
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0PROT_EXEC | PROT_READ | PROT_WRIT=
E,
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0MAP_ANON | MAP_FIXED | MAP_SHARED=
,
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0-1, 0) =3D=3D MAP_FAILED) {
>> =A0 =A0 =A0 =A0 perror("Error mapping HMA, HMA disabled: ");
>> =A0 =A0 =A0 =A0 HMA_a20 =3D -1;
>> =A0 =A0 =A0 =A0 close(HMA_fd_off);
>> =A0 =A0 =A0 =A0 close(HMA_fd_on);
>> =A0 =A0 =A0 =A0 return;
>> =A0 =A0 }
>>
>> 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. =A0Now=
,
> 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 of=
fset.
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