For system mode, we can rarely support the amount of RAM that
the guest requires. TCG emulation is restricted to round-robin
mode, which solves many of the atomicity issues, but not those
associated with virtio.  In any case, round-robin does nothing
to help the speed of emulation.

For user mode, most emulation does not succeed at all.  Most
of the time we cannot even load 64-bit non-PIE binaries due
to lack of a 64-bit address space.  Threads are run in
parallel, not round-robin, which means that atomicity
is not handled.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 meson.build | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/meson.build b/meson.build
index 85317cd63f..ec51827f40 100644
--- a/meson.build
+++ b/meson.build
@@ -3185,6 +3185,9 @@ if host_os == 'windows'
   endif
 endif
 
+# Detect host pointer size for the target configuration loop.
+host_long_bits = cc.sizeof('void *') * 8
+
 ########################
 # Target configuration #
 ########################
@@ -3277,8 +3280,14 @@ foreach target : target_dirs
     }
   endif
 
+  config_target += keyval.load('configs/targets' / target + '.mak')
+
   target_kconfig = []
   foreach sym: accelerators
+    # Disallow 64-bit on 32-bit emulation and virtualization
+    if host_long_bits < config_target['TARGET_LONG_BITS'].to_int()
+      continue
+    endif
     if sym == 'CONFIG_TCG' or target in accelerator_targets.get(sym, [])
       config_target += { sym: 'y' }
       config_all_accel += { sym: 'y' }
@@ -3292,9 +3301,6 @@ foreach target : target_dirs
     error('No accelerator available for target @0@'.format(target))
   endif
 
-  config_target += keyval.load('configs/targets' / target + '.mak')
-  config_target += { 'TARGET_' + config_target['TARGET_ARCH'].to_upper(): 'y' }
-
   if 'TARGET_NEED_FDT' in config_target and not fdt.found()
     if default_targets
       warning('Disabling ' + target + ' due to missing libfdt')
@@ -3307,6 +3313,7 @@ foreach target : target_dirs
   actual_target_dirs += target
 
   # Add default keys
+  config_target += { 'TARGET_' + config_target['TARGET_ARCH'].to_upper(): 'y' }
   if 'TARGET_BASE_ARCH' not in config_target
     config_target += {'TARGET_BASE_ARCH': config_target['TARGET_ARCH']}
   endif
-- 
2.43.0