[Qemu-devel] linux-user/mmap.c query

[Qemu-devel] linux-user/mmap.c query

[cb-qemu]

Hi Fabrice and everyone

I'm trying to use qemu-arm to run some statically linked linux binaries, and
I've come across an issue with the target_mmap function. The test at line 185:
    if (offset & ~TARGET_PAGE_MASK)
        return -EINVAL;
seems to be unnecessary as there is code to handle a non-aligned offset later
on in the function which is introduced by the comment
    /* worst case: we cannot map the file because the offset is not
       aligned, so we read it */

In addition, there seems to be an inconsistency in the way errors are reported
from target_mmap and what is expected by linux-user/elfload.c. target_mmap()
returns -EINVAL, but elfload.c expects errors to be reported with -1 and errno
to be set.

The following (totally minimal) patch enables me to run a few simple statically
linked ARM binaries. (This is just to make it clear the change I am talking
about).

Once this is addressed I run into problems with binaries which execute code
from writable pages - the code pages are marked non-writable by tb_link_phys()
but segfaults arising from writes are not handled. I haven't fully investigated
this problem yet. Is this supposed to work? I'll try and create a test case if
I don't make any progress on this.

BTW, is it possible to run qemu-arm under gdb and get breakpoints working? When
I try, gdb complains because the qemu binary is remapped somewhere else in the
addres space.

Regards
Charlie

--- linux-user/mmap.c   5 Jul 2004 21:25:16 -0000       1.7
+++ linux-user/mmap.c   22 Sep 2004 20:18:53 -0000
@@ -182,7 +182,7 @@
     }
 #endif
 
-    if (offset & ~TARGET_PAGE_MASK)
+    if (offset & ~TARGET_PAGE_MASK && 0)
         return -EINVAL;
 
     len = TARGET_PAGE_ALIGN(len);

Re: [Qemu-devel] linux-user/mmap.c query

[Paul Brook]

On Wednesday 22 September 2004 23:16, cb-qemu@fish.zetnet.co.uk wrote:
> BTW, is it possible to run qemu-arm under gdb and get breakpoints working?
> When I try, gdb complains because the qemu binary is remapped somewhere
> else in the addres space.

Configure with --static.

> --- linux-user/mmap.c   5 Jul 2004 21:25:16 -0000       1.7
> +++ linux-user/mmap.c   22 Sep 2004 20:18:53 -0000
> @@ -182,7 +182,7 @@
>      }
>  #endif
>  
> -    if (offset & ~TARGET_PAGE_MASK)
> +    if (offset & ~TARGET_PAGE_MASK && 0)
>          return -EINVAL;
>  
>      len = TARGET_PAGE_ALIGN(len);

Isn't this just papering over the problem? What about the other places in that 
function which return -EINVAL?

Also the later code handles host misalignment, whereas this test if for target 
misalignment.

Paul