Don't require an exe_wrapper when cross-compiling 32-bit on 64-bit

Almost all 64-bit x86 OSes can run 32-bit x86 binaries natively. Detect
that case and don't require an exe wrapper.

mesonbuild/backend/backends.py

@@ -315,7 +315,9 @@ class Backend():
                 fname = exe.fullpath
             else:
                 fname = [os.path.join(self.environment.get_build_dir(), self.get_target_filename(t.get_exe()))]
-            is_cross = self.environment.is_cross_build() and self.environment.cross_info.need_cross_compiler()
+            is_cross = self.environment.is_cross_build() and \
+                self.environment.cross_info.need_cross_compiler() and \
+                self.environment.cross_info.need_exe_wrapper()
             if is_cross:
                 exe_wrapper = self.environment.cross_info.config['binaries'].get('exe_wrapper', None)
             else:
@@ -366,8 +368,9 @@ class Backend():
 
     def exe_object_to_cmd_array(self, exe):
         if self.environment.is_cross_build() and \
+           self.environment.cross_info.need_exe_wrapper() and \
            isinstance(exe, build.BuildTarget) and exe.is_cross:
-            if 'exe_wrapper'  not in self.environment.cross_info:
+            if 'exe_wrapper' not in self.environment.cross_info.config:
                 s = 'Can not use target %s as a generator because it is cross-built\n'
                 s += 'and no exe wrapper is defined. You might want to set it to native instead.'
                 s = s % exe.name

mesonbuild/backend/ninjabackend.py

@@ -394,9 +394,11 @@ int dummy;
         if isinstance(texe, build.Executable):
             abs_exe = os.path.join(self.environment.get_build_dir(), self.get_target_filename(texe))
             deps.append(self.get_target_filename(texe))
-            if self.environment.is_cross_build() \
-                and self.environment.cross_info.config['binaries'].get('exe_wrapper', None) is not None:
-                cmd += [self.environment.cross_info.config['binaries']['exe_wrapper']]
+            if self.environment.is_cross_build() and \
+               self.environment.cross_info.need_exe_wrapper():
+                exe_wrap = self.environment.cross_info.config['binaries'].get('exe_wrapper', None)
+                if exe_wrap is not None:
+                    cmd += [exe_wrap]
             cmd.append(abs_exe)
         else:
             cmd.append(target.command)

mesonbuild/environment.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import os, re, subprocess
+import os, re, subprocess, platform
 from . import coredata, mesonlib
 from .compilers import *
 import configparser
@@ -52,6 +52,26 @@ def detect_ninja():
         if p.returncode == 0:
             return n
 
+def detect_cpu_family():
+    """
+    Python is inconsistent in its platform module.
+    It returns different values for the same cpu.
+    For x86 it might return 'x86', 'i686' or somesuch.
+    Do some canonicalization.
+    """
+    trial = platform.machine().lower()
+    if trial.startswith('i') and trial.endswith('86'):
+        return 'x86'
+    if trial.startswith('arm'):
+        return 'arm'
+    if trial == 'amd64':
+        return 'x86_64'
+    # Add fixes here as bugs are reported.
+    return trial
+
+def detect_system():
+    return platform.system().lower()
+
 
 class Environment():
     private_dir = 'meson-private'
@@ -181,7 +201,10 @@ class Environment():
             compilers = [self.cross_info.config['binaries']['c']]
             ccache = []
             is_cross = True
+            if self.cross_info.need_exe_wrapper():
                 exe_wrap = self.cross_info.config['binaries'].get('exe_wrapper', None)
+            else:
+                exe_wrap = []
         elif evar in os.environ:
             compilers = os.environ[evar].split()
             ccache = []
@@ -239,7 +262,10 @@ class Environment():
         if self.is_cross_build() and want_cross:
             compilers = [self.cross_info['fortran']]
             is_cross = True
+            if self.cross_info.need_exe_wrapper():
                 exe_wrap = self.cross_info.get('exe_wrapper', None)
+            else:
+                exe_wrap = []
         elif evar in os.environ:
             compilers = os.environ[evar].split()
             is_cross = False
@@ -308,7 +334,10 @@ class Environment():
             compilers = [self.cross_info.config['binaries']['cpp']]
             ccache = []
             is_cross = True
+            if self.cross_info.need_exe_wrapper():
                 exe_wrap = self.cross_info.config['binaries'].get('exe_wrapper', None)
+            else:
+                exe_wrap = []
         elif evar in os.environ:
             compilers = os.environ[evar].split()
             ccache = []
@@ -364,7 +393,10 @@ class Environment():
         if self.is_cross_build() and want_cross:
             exelist = [self.cross_info['objc']]
             is_cross = True
+            if self.cross_info.need_exe_wrapper():
                 exe_wrap = self.cross_info.get('exe_wrapper', None)
+            else:
+                exe_wrap = []
         else:
             exelist = self.get_objc_compiler_exelist()
             is_cross = False
@@ -394,7 +426,10 @@ class Environment():
         if self.is_cross_build() and want_cross:
             exelist = [self.cross_info['objcpp']]
             is_cross = True
+            if self.cross_info.need_exe_wrapper():
                 exe_wrap = self.cross_info.get('exe_wrapper', None)
+            else:
+                exe_wrap = []
         else:
             exelist = self.get_objcpp_compiler_exelist()
             is_cross = False
@@ -700,3 +735,12 @@ class CrossBuildInfo():
     # But not when cross compiling a cross compiler.
     def need_cross_compiler(self):
         return 'host_machine' in self.config
+
+    def need_exe_wrapper(self):
+        if self.has_host() and detect_cpu_family() == 'x86_64' and \
+           self.config['host_machine']['cpu_family'] == 'x86' and \
+           self.config['host_machine']['system'] == detect_system():
+            # Can almost always run 32-bit binaries on 64-bit natively if the
+            # host and build systems are the same
+            return False
+        return True

mesonbuild/interpreter.py

@@ -322,24 +322,14 @@ class BuildMachine(InterpreterObject):
                              'endian' : self.endian_method,
                             })
 
-    # Python is inconsistent in its platform module.
-    # It returns different values for the same cpu.
-    # For x86 it might return 'x86', 'i686' or somesuch.
-    # Do some canonicalization.
     def cpu_family_method(self, args, kwargs):
-        trial = platform.machine().lower()
-        if trial.startswith('i') and trial.endswith('86'):
-            return 'x86'
-        if trial.startswith('arm'):
-            return 'arm'
-        # Add fixes here as bugs are reported.
-        return trial
+        return environment.detect_cpu_family()
 
     def cpu_method(self, args, kwargs):
         return platform.machine().lower()
 
     def system_method(self, args, kwargs):
-        return platform.system().lower()
+        return environment.detect_system()
 
     def endian_method(self, args, kwargs):
         return sys.byteorder
@@ -883,9 +873,16 @@ class MesonMain(InterpreterObject):
         return self.interpreter.environment.build_dir
 
     def has_exe_wrapper_method(self, args, kwargs):
-        if self.is_cross_build_method(None, None) and 'binaries' in self.build.environment.cross_info.config:
-            return 'exe_wrap' in self.build.environment.cross_info.config['binaries']
-        return True  # This is semantically confusing.
+        if self.is_cross_build_method(None, None) and \
+           'binaries' in self.build.environment.cross_info.config and \
+           self.build.environment.cross_info.need_exe_wrapper():
+            exe_wrap = self.build.environment.cross_info.config['binaries'].get('exe_wrap', None)
+            if exe_wrap is None:
+                return False
+        # We return True when exe_wrap is defined, when it's not needed, and
+        # when we're compiling natively. The last two are semantically confusing.
+        # Need to revisit this.
+        return True
 
     def is_cross_build_method(self, args, kwargs):
         return self.build.environment.is_cross_build()