From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: cygwin@cygwin.com
Subject: Re: mmap failing with MAP_FIXED
Date: Mon, 4 Jul 2022 10:19:43 +0200 [thread overview]
Message-ID: <YsKin3kIuaUsmJXE@calimero.vinschen.de> (raw)
In-Reply-To: <000001d88d68$4d5a7a40$e80f6ec0$@cl.cam.ac.uk>
On Jul 1 17:33, David Allsopp wrote:
> This program fails at the second mmap call with EINVAL:
>
> #include <stdio.h>
> #include <sys/mman.h>
> #include <error.h>
>
> int main (void) {
> void * mem;
> /* Reserve 256MB address space for the minor heaps */
> mem = mmap(0, 268439552, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> if (mem == MAP_FAILED)
> error(1, 0, "Reservation failed");
> /* Commit the first 2MB heap */
> if (mmap(mem, 2097152, PROT_READ | PROT_WRITE, MAP_PRIVATE |
> MAP_ANONYMOUS | MAP_FIXED, -1, 0) == MAP_FAILED)
> error(1, 0, "Commit failed");
> }
>
> Is this something that's expected to fail for Cygwin, or a bug?
Depends on the point of view, I guess. PROT_NONE pages are not just
reserved pages in the Windows sense. mmap'ed pages are always commited
and PROT_NONE is just a page protection. Using mmap to change the page
protection of already commited memory is not implemented. To change
this, use mprotect.
Corinna
prev parent reply other threads:[~2022-07-04 8:19 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-01 16:33 David Allsopp
2022-07-01 16:45 ` gs-cygwin.com
2022-07-04 8:19 ` Corinna Vinschen [this message]
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