Allow selecting the dynamic linker

This uses the normal meson mechanisms, an LD environment variable or via
cross/native files.

Fixes: mesonbuild#6057

docs/markdown/snippets/linker_override.md

@@ -0,0 +1,17 @@
+## Generic Overrider for Dynamic Linker selection
+
+Previous to meson 0.52.0 you set the dynamic linker using compiler specific
+flags passed via language flags and hoped things worked out. In meson 0.52.0
+meson started detecting the linker and making intelligent decisions about
+using it. Unfortunately this broke choosing a non-default linker.
+
+Now there is a generic mechanism for doing this, you may use the LD
+environment variable (with normal meson environment variable rules), or add
+the following to a cross or native file:
+
+```ini
+[binaries]
+ld = 'gold'
+```
+
+And meson will select the linker if possible.

mesonbuild/compilers/compilers.py

@@ -1192,6 +1192,12 @@ def get_dependency_compile_args(self, dep):
     def get_dependency_link_args(self, dep):
         return dep.get_link_args()
 
+    @classmethod
+    def use_linker_args(cls, linker: str) -> typing.List[str]:
+        """Get a list of arguments to pass to the compiler to set the linker.
+        """
+        return []
+
 
 def get_largefile_args(compiler):
     '''

mesonbuild/compilers/mixins/gnu.py

@@ -299,6 +299,10 @@ def get_include_args(self, path: str, is_system: bool) -> typing.List[str]:
             return ['-isystem' + path]
         return ['-I' + path]
 
+    @classmethod
+    def use_linker_args(cls, linker: str) -> typing.List[str]:
+        return ['-fuse-ld={}'.format(linker)]
+
 
 class GnuCompiler(GnuLikeCompiler):
     """

mesonbuild/compilers/mixins/visualstudio.py

@@ -381,3 +381,7 @@ def has_func_attribute(self, name: str, env: 'Environment') -> typing.Tuple[bool
 
     def get_argument_syntax(self) -> str:
         return 'msvc'
+
+    @classmethod
+    def use_linker_args(cls, linker: str) -> typing.List[str]:
+        return []

mesonbuild/compilers/rust.py

@@ -32,7 +32,7 @@
 
 class RustCompiler(Compiler):
 
-    LINKER_PREFIX = '-Wl,'
+    # rustc doesn't invoke the compiler itself, it doesn't need a LINKER_PREFIX
 
     def __init__(self, exelist, version, for_machine: MachineChoice,
                  is_cross, info: 'MachineInfo', exe_wrapper=None, **kwargs):
@@ -109,3 +109,7 @@ def compute_parameters_with_absolute_paths(self, parameter_list, build_dir):
 
     def get_std_exe_link_args(self):
         return []
+
+    # Rust does not have a use_linker_args because it dispatches to a gcc-like
+    # C compiler for dynamic linking, as such we invoke the C compiler's
+    # use_linker_args method instead.

mesonbuild/envconfig.py

@@ -309,7 +309,9 @@ def __init__(
         'strip': 'STRIP',
         'ar': 'AR',
         'windres': 'WINDRES',
+        'ld': 'LD',
 
+        # Other tools
         'cmake': 'CMAKE',
         'qmake': 'QMAKE',
         'pkgconfig': 'PKG_CONFIG',

mesonbuild/linkers.py

@@ -247,17 +247,21 @@ class DynamicLinker(metaclass=abc.ABCMeta):
     }  # type: typing.Dict[str, typing.List[str]]
 
     def _apply_prefix(self, arg: str) -> typing.List[str]:
-        if isinstance(self.prefix_arg, str):
+        if self.prefix_arg is None:
+            return [arg]
+        elif isinstance(self.prefix_arg, str):
             return [self.prefix_arg + arg]
         return self.prefix_arg + [arg]
 
     def __init__(self, exelist: typing.List[str], for_machine: mesonlib.MachineChoice,
-                 id_: str, prefix_arg: typing.Union[str, typing.List[str]], *, version: str = 'unknown version'):
+                 id_: str, prefix_arg: typing.Union[str, typing.List[str]],
+                 always_args: typing.List[str], *, version: str = 'unknown version'):
         self.exelist = exelist
         self.for_machine = for_machine
         self.version = version
         self.id = id_
         self.prefix_arg = prefix_arg
+        self.always_args = always_args
 
     def __repr__(self) -> str:
         return '<{}: v{} `{}`>'.format(type(self).__name__, self.version, ' '.join(self.exelist))
@@ -276,7 +280,7 @@ def get_accepts_rsp(self) -> bool:
         return mesonlib.is_windows()
 
     def get_always_args(self) -> typing.List[str]:
-        return []
+        return self.always_args.copy()
 
     def get_lib_prefix(self) -> str:
         return ''
@@ -715,7 +719,7 @@ class ArmDynamicLinker(PosixDynamicLinkerMixin, DynamicLinker):
 
     def __init__(self, for_machine: mesonlib.MachineChoice,
                  *, version: str = 'unknown version'):
-        super().__init__(['armlink'], for_machine, 'armlink', '',
+        super().__init__(['armlink'], for_machine, 'armlink', '', [],
                          version=version)
 
     def get_accepts_rsp(self) -> bool:
@@ -853,33 +857,33 @@ class MSVCDynamicLinker(VisualStudioLikeLinkerMixin, DynamicLinker):
 
     """Microsoft's Link.exe."""
 
-    def __init__(self, for_machine: mesonlib.MachineChoice, *,
+    def __init__(self, for_machine: mesonlib.MachineChoice, always_args: typing.List[str], *,
                  exelist: typing.Optional[typing.List[str]] = None,
                  prefix: typing.Union[str, typing.List[str]] = '',
                  machine: str = 'x86', version: str = 'unknown version'):
         super().__init__(exelist or ['link.exe'], for_machine, 'link',
-                         prefix, machine=machine, version=version)
+                         prefix, always_args, machine=machine, version=version)
 
 
 class ClangClDynamicLinker(VisualStudioLikeLinkerMixin, DynamicLinker):
 
     """Clang's lld-link.exe."""
 
-    def __init__(self, for_machine: mesonlib.MachineChoice, *,
+    def __init__(self, for_machine: mesonlib.MachineChoice, always_args: typing.List[str], *,
                  exelist: typing.Optional[typing.List[str]] = None,
                  prefix: typing.Union[str, typing.List[str]] = '',
                  version: str = 'unknown version'):
-        super().__init__(exelist or ['lld-link.exe'], for_machine,
-                         'lld-link', prefix, version=version)
+        super().__init__(exelist or ['lld-link.exe'], for_machine, 'lld-link',
+                         prefix, always_args, version=version)
 
 
 class XilinkDynamicLinker(VisualStudioLikeLinkerMixin, DynamicLinker):
 
     """Intel's Xilink.exe."""
 
-    def __init__(self, for_machine: mesonlib.MachineChoice,
+    def __init__(self, for_machine: mesonlib.MachineChoice, always_args: typing.List[str],
                  *, version: str = 'unknown version'):
-        super().__init__(['xilink.exe'], for_machine, 'xilink', '', version=version)
+        super().__init__(['xilink.exe'], for_machine, 'xilink', '', always_args, version=version)
 
 
 class SolarisDynamicLinker(PosixDynamicLinkerMixin, DynamicLinker):
@@ -936,7 +940,7 @@ def __init__(self, for_machine: mesonlib.MachineChoice,
                  *, version: str = 'unknown version'):
         # Use optlink instead of link so we don't interfer with other link.exe
         # implementations.
-        super().__init__(['optlink.exe'], for_machine, 'optlink', prefix_arg='', version=version)
+        super().__init__(['optlink.exe'], for_machine, 'optlink', '', [], version=version)
 
     def get_allow_undefined_args(self) -> typing.List[str]:
         return []

run_unittests.py

@@ -442,7 +442,7 @@ def test_compiler_args_class(self):
     def test_compiler_args_class_gnuld(self):
         cargsfunc = mesonbuild.compilers.CompilerArgs
         ## Test --start/end-group
-        linker = mesonbuild.linkers.GnuDynamicLinker([], MachineChoice.HOST, 'fake', '-Wl,')
+        linker = mesonbuild.linkers.GnuDynamicLinker([], MachineChoice.HOST, 'fake', '-Wl,', [])
         gcc = mesonbuild.compilers.GnuCCompiler([], 'fake', False, MachineChoice.HOST, mock.Mock(), linker=linker)
         ## Ensure that the fake compiler is never called by overriding the relevant function
         gcc.get_default_include_dirs = lambda: ['/usr/include', '/usr/share/include', '/usr/local/include']
@@ -471,7 +471,7 @@ def test_compiler_args_class_gnuld(self):
     def test_compiler_args_remove_system(self):
         cargsfunc = mesonbuild.compilers.CompilerArgs
         ## Test --start/end-group
-        linker = mesonbuild.linkers.GnuDynamicLinker([], MachineChoice.HOST, 'fake', '-Wl,')
+        linker = mesonbuild.linkers.GnuDynamicLinker([], MachineChoice.HOST, 'fake', '-Wl,', [])
         gcc = mesonbuild.compilers.GnuCCompiler([], 'fake', False, MachineChoice.HOST, mock.Mock(), linker=linker)
         ## Ensure that the fake compiler is never called by overriding the relevant function
         gcc.get_default_include_dirs = lambda: ['/usr/include', '/usr/share/include', '/usr/local/include']