Re: [Qemu-devel] [PATCH] linux-user: fix tcg/mmap test

[Peter Maydell]

On 19 September 2016 at 01:24, Marc-André Lureau
<address@hidden> wrote:
> tests/tcg/mmap test fails with values other than default target page
> size. When creating a map beyond EOF, extra anonymous pages are added up
> to the target page boundary. Currently, this operation is performed only
> when qemu_real_host_page_size < TARGET_PAGE_SIZE, but it should be
> performed if the configured page size (qemu -p) is larger than
> qemu_real_host_page_size too.

What is the purpose of the -p option, does anybody know?
I don't see why you'd want to be able to manually set what QEMU
thinks the host page size is, it seems like it would mostly
only break things.

> (also fixes some style issues to please checkpatch)
>
> Signed-off-by: Marc-André Lureau <address@hidden>
> ---
>  linux-user/mmap.c | 27 ++++++++++++++-------------
>  1 file changed, 14 insertions(+), 13 deletions(-)
>
> diff --git a/linux-user/mmap.c b/linux-user/mmap.c
> index c4371d9..4bf79b5 100644
> --- a/linux-user/mmap.c
> +++ b/linux-user/mmap.c
> @@ -415,31 +415,32 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, 
> int prot,
>      }
>
>      /* When mapping files into a memory area larger than the file, accesses
> -       to pages beyond the file size will cause a SIGBUS.
> +       to pages beyond the file size will cause a SIGBUS.
>
>         For example, if mmaping a file of 100 bytes on a host with 4K pages
>         emulating a target with 8K pages, the target expects to be able to
>         access the first 8K. But the host will trap us on any access beyond
> -       4K.
> +       4K.
>
>         When emulating a target with a larger page-size than the hosts, we
>         may need to truncate file maps at EOF and add extra anonymous pages
>         up to the targets page boundary.  */

This comment states what this code is trying to do (handle
the case where the target page size is larger than the
host page size)...

> -    if ((qemu_real_host_page_size < TARGET_PAGE_SIZE)
> -        && !(flags & MAP_ANONYMOUS)) {
> -       struct stat sb;
> +    if ((qemu_real_host_page_size < qemu_host_page_size) &&
> +        !(flags & MAP_ANONYMOUS)) {

...but this changes the code so it is no longer doing that.

> +        struct stat sb;
>
> -       if (fstat (fd, &sb) == -1)
> -           goto fail;
> +        if (fstat(fd, &sb) == -1) {
> +            goto fail;
> +        }
>
>         /* Are we trying to create a map beyond EOF?.  */
> -       if (offset + len > sb.st_size) {
> -           /* If so, truncate the file map at eof aligned with
> -              the hosts real pagesize. Additional anonymous maps
> -              will be created beyond EOF.  */
> -           len = REAL_HOST_PAGE_ALIGN(sb.st_size - offset);
> -       }
> +        if (offset + len > sb.st_size) {
> +            /* If so, truncate the file map at eof aligned with
> +               the hosts real pagesize. Additional anonymous maps
> +               will be created beyond EOF.  */
> +            len = REAL_HOST_PAGE_ALIGN(sb.st_size - offset);
> +        }
>      }
>
>      if (!(flags & MAP_FIXED)) {
> --
> 2.10.0

thanks
-- PMM