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

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

[Marc-André Lureau]

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.

(also fixes some style issues to please checkpatch)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 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.  */
 
-    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)) {
+        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

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

[Peter Maydell]

On 19 September 2016 at 01:24, Marc-André Lureau
<marcandre.lureau@redhat.com> 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 <marcandre.lureau@redhat.com>
> ---
>  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