scons: Simplify kvm architecture compatibility check.

The original implementation had a function we'd call back into later
which checked if a given ISA has KVM support on the current host.
Instead, this change reverse that and statically figures out which
single target ISA could possibly run under KVM on this host. Then later,
we can just check if the ISA we're trying to build is that one.

Change-Id: I3e7e06180983dfcc4611181718eb5d6210844d36
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40870
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>

diff --git a/SConstruct b/SConstruct
index 09029f63737ca2620422acf6dc136b963bb92e6c..210f813646e6583435b2e1135a5f7e882f7ad8c9 100755 (executable)
--- a/SConstruct
+++ b/SConstruct
@@ -674,39 +674,26 @@ have_tuntap = conf.CheckHeader('linux/if_tun.h', '<>')
 if not have_tuntap:
     print("Info: Compatible header file <linux/if_tun.h> not found.")
 
-# x86 needs support for xsave. We test for the structure here since we
-# won't be able to run new tests by the time we know which ISA we're
-# targeting.
-have_kvm_xsave = conf.CheckTypeSize('struct kvm_xsave',
-                                    '#include <linux/kvm.h>') != 0
-
-# Check if the requested target ISA is compatible with the host
-def is_isa_kvm_compatible(isa):
-    try:
-        import platform
-        host_isa = platform.machine()
-    except:
-        warning("Failed to determine host ISA.")
-        return False
-
-    if not have_posix_timers:
-        warning("Can not enable KVM, host seems to lack support "
-                "for POSIX timers")
-        return False
-
-    if isa == "arm":
-        return host_isa in ( "armv7l", "aarch64" )
-    elif isa == "x86":
-        if host_isa != "x86_64":
-            return False
-
-        if not have_kvm_xsave:
-            warning("KVM on x86 requires xsave support in kernel headers.")
-            return False
-
-        return True
+# Determine what ISA KVM can support on this host.
+kvm_isa = None
+host_isa = None
+try:
+    import platform
+    host_isa = platform.machine()
+except:
+    pass
+
+if not host_isa:
+    warning("Failed to determine host ISA.")
+elif not have_posix_timers:
+    warning("Cannot enable KVM, host seems to lack support for POSIX timers")
+elif host_isa in ('armv7l', 'aarch64'):
+    kvm_isa = 'arm'
+elif host_isa == 'x86_64':
+    if conf.CheckTypeSize('struct kvm_xsave', '#include <linux/kvm.h>') != 0:
+        kvm_isa = 'x86'
     else:
-        return False
+        warning("KVM on x86 requires xsave support in kernel headers.")
 
 
 # Check if the exclude_host attribute is available. We want this to
@@ -1044,9 +1031,9 @@ Build variables for {dir}:
         if not have_kvm:
             warning("Can not enable KVM, host seems to lack KVM support")
             env['USE_KVM'] = False
-        elif not is_isa_kvm_compatible(env['TARGET_ISA']):
-            print("Info: KVM support disabled due to unsupported host and "
-                  "target ISA combination")
+        elif kvm_isa != env['TARGET_ISA']:
+            print("Info: KVM for %s not supported on %s host." %
+                  (env['TARGET_ISA'], kvm_isa))
             env['USE_KVM'] = False
 
     if env['USE_TUNTAP']: