[Qemu-devel] linux-user mremap()

[Qemu-devel] linux-user mremap()

[Vince Weaver]

Until the linux-user mremap() problem is fixed (the one where a 64-bit 
value can be returned even on a 32-bit target), might it make sense to 
apply a patch like this?

This will at least let users know what the problem is, instead of just 
segfaulting.

Vince




Index: mmap.c
===================================================================
--- mmap.c	(revision 5321)
+++ mmap.c	(working copy)
@@ -538,6 +538,13 @@
      mmap_lock();
      /* XXX: use 5 args syscall */
      host_addr = (long)mremap(g2h(old_addr), old_size, new_size, flags);
+#if TARGET_ABI_BITS == 32
+    if (host_addr > 0xffffffff) {
+       printf("ERROR!  mremap() returned 64-bit value on 32-bit target!\n\n");
+       exit(-1); 
+    }
+#endif 
+
      if (host_addr == -1) {
          new_addr = -1;
      } else {

Re: [Qemu-devel] linux-user mremap()

[Kirill A. Shutemov]

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On Fri, Sep 26, 2008 at 02:24:43PM -0400, Vince Weaver wrote:
> 
> Until the linux-user mremap() problem is fixed (the one where a 64-bit 
> value can be returned even on a 32-bit target), might it make sense to 
> apply a patch like this?
> 
> This will at least let users know what the problem is, instead of just 
> segfaulting.
> 
> Vince

If host is x86_64, use MAP_32BIT.

> 
> 
> 
> 
> Index: mmap.c
> ===================================================================
> --- mmap.c	(revision 5321)
> +++ mmap.c	(working copy)
> @@ -538,6 +538,13 @@
>       mmap_lock();
>       /* XXX: use 5 args syscall */
>       host_addr = (long)mremap(g2h(old_addr), old_size, new_size, flags);
> +#if TARGET_ABI_BITS == 32
> +    if (host_addr > 0xffffffff) {
> +       printf("ERROR!  mremap() returned 64-bit value on 32-bit target!\n\n");
> +       exit(-1); 
> +    }
> +#endif 
> +
>       if (host_addr == -1) {
>           new_addr = -1;
>       } else {
> 
> 

-- 
Regards,  Kirill A. Shutemov
 + Belarus, Minsk
 + ALT Linux Team, http://www.altlinux.com/

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Re: [Qemu-devel] linux-user mremap()

[Vince Weaver]

> If host is x86_64, use MAP_32BIT.

I don't think that works for mremap(), hence the problem.

In any case, even if it does fix it for x86_64, simply crashing qemu with 
a segfault on other architectures still isn't a good thing to do.

Vince