qemu: Add some user space mmap tweaks to address musl 32 bit

When using qemu-i386 to build qemux86 webkitgtk on musl, 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.

A better return value for the other cases of invalid addresses is EINVAL
rather than ENOMEM so adjust the other part of the test to this.

Upstream-Status: Submitted [https://lists.gnu.org/archive/html/qemu-devel/2021-01/msg01355.html]
Signed-off-by: Richard Purdie <[email protected]

Author: rpurdie

linux-user/mmap.c

@@ -1108,12 +1108,16 @@ abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
     int prot;
     void *host_addr;
 
-    if (!guest_range_valid_untagged(old_addr, old_size) ||
-        ((flags & MREMAP_FIXED) &&
+    if (!guest_range_valid_untagged(old_addr, old_size)) {
+        errno = EFAULT;
+        return -1;
+    }
+    
+    if (((flags & MREMAP_FIXED) &&
          !guest_range_valid_untagged(new_addr, new_size)) ||
         ((flags & MREMAP_MAYMOVE) == 0 &&
          !guest_range_valid_untagged(old_addr, new_size))) {
-        errno = ENOMEM;
+        errno = EINVAL;
         return -1;
     }