[RFC PATCH] linux-user/mmap: Return EFAULT for invalid addresses

[Richard Purdie <richard.purdie@linuxfoundation.org>]

When using qemu-i386 to run gobject introspection parts of a webkitgtk 
build using musl as libc on a 64 bit host, it sits in an infinite loop 
of mremap calls of ever decreasing/increasing addresses.

I suspect something in the musl memory allocation code loops indefinitely
if it only sees ENOMEM and only exits when it hits EFAULT.

According to the docs, trying to mremap outside the address space
can/should return EFAULT and changing this allows the build to succeed.

There was previous discussion of this as it used to work before qemu 2.11
and we've carried hacks to work around it since, this appears to be a
better fix of the real issue?

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org

Index: qemu-5.2.0/linux-user/mmap.c
===================================================================
--- qemu-5.2.0.orig/linux-user/mmap.c
+++ qemu-5.2.0/linux-user/mmap.c
@@ -727,7 +727,7 @@ abi_long target_mremap(abi_ulong old_add
          !guest_range_valid(new_addr, new_size)) ||
         ((flags & MREMAP_MAYMOVE) == 0 &&
          !guest_range_valid(old_addr, new_size))) {
-        errno = ENOMEM;
+        errno = EFAULT;
         return -1;
     }