Re: kern/56819: netbsd32 compat does not handle sign-extended addresses

[Martin Husemann <martin%duskware.de@localhost>]

The following reply was made to PR kern/56819; it has been noted by GNATS.

From: Martin Husemann <martin%duskware.de@localhost>
To: Michael van Elst <mlelstv%serpens.de@localhost>
Cc: gnats-bugs%netbsd.org@localhost
Subject: Re: kern/56819: netbsd32 compat does not handle sign-extended
 addresses
Date: Sat, 7 May 2022 16:20:25 +0200

 On Sat, May 07, 2022 at 03:28:23PM +0200, Michael van Elst wrote:
 > A 32bit process running on an aarch64 system has a 4GB address space,
 > the "cut" (VM_MAXUSER_ADDRESS32) is at 0xfffff000, i.e. only the last
 > page doesn't exist. This is different from a native 32bit arm process
 > where the "cut" is at 2GB, so "negative" addresses are not used.
 
 I'm not sure I follow - on sparc we have a full 4G adress space for both
 native 32bit and compat32 userland and haven't experienced the problem
 so far (but ASLR has some MD quirks for 32bit userland IIRC).
 
 #define VM_MAXUSER_ADDRESS32        ((vaddr_t)(0x00000000ffffffffL&~PGOFSET))
 
 Martin