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

@@ -1176,6 +1176,16 @@ 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.Optional[typing.List[str]]:
+        """Get a list of arguments to pass to the compiler to set the linker.
+
+        Returns None if the compiler does not invoke the linker.
+        :raises MesonException: When meson doesn't know how to map a specific
+            linker to a compiler
+        """
+        raise mesonlib.MesonException('Cannot use linker {} with {}'.format(linker, self.id))
+
 
 def get_largefile_args(compiler):
     '''

mesonbuild/compilers/mixins/gnu.py

@@ -299,6 +299,12 @@ 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]:
+        if linker not in {'bfd', 'gold', 'lld'}:
+            return super().use_linker_args(linker)
+        return ['-fuse-ld={}'.format(linker)]
+
 
 class GnuCompiler(GnuLikeCompiler):
     """

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

@@ -252,12 +252,14 @@ def _apply_prefix(self, arg: str) -> typing.List[str]:
         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 +278,7 @@ 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 ''
@@ -713,7 +715,7 @@ 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:
@@ -851,33 +853,33 @@ 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, machine=machine, 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):

run_unittests.py

@@ -445,7 +445,7 @@ 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']
@@ -474,7 +474,7 @@ 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']