sd-boot: Let the compiler invoke the linker for us

For LTO to work, the linker has to be called with some magic sauce arguments.
And the easiest way to get those is to just let the compiler to the job for us.

meson_options.txt

@@ -411,7 +411,9 @@ option('gnu-efi', type : 'combo', choices : ['auto', 'true', 'false'],
        description : 'gnu-efi support for sd-boot')
 option('efi-cc', type : 'array',
        description : 'the compiler to use for EFI modules')
-option('efi-ld', type : 'string', value : 'ld',
+# Note that LLD does not support PE/COFF relocations
+# https://lists.llvm.org/pipermail/llvm-dev/2021-March/149234.html
+option('efi-ld', type : 'combo', choices : ['bfd', 'gold'],
        description : 'the linker to use for EFI modules')
 option('efi-libdir', type : 'string',
        description : 'path to the EFI lib directory')

src/boot/efi/meson.build

@@ -48,14 +48,6 @@ if efi_cc.length() == 0
         efi_cc = cc.cmd_array()
 endif
 
-efi_ld = find_program(get_option('efi-ld'))
-efi_ld_name = efi_ld.path().split('/')[-1]
-if efi_ld_name == 'lld' or efi_ld_name == 'ld.lld'
-        # LLVM/LLD does not support PE/COFF relocations
-        # https://lists.llvm.org/pipermail/llvm-dev/2021-March/149234.html
-        error('LLVM/lld does not support PE/COFF relocations. Use different linker for EFI image.')
-endif
-
 efi_libdir = ''
 foreach dir : [get_option('efi-libdir'),
                '/usr/lib/gnuefi' / efi_arch[0],
@@ -260,26 +252,52 @@ foreach arg : get_option('c_args')
         endif
 endforeach
 
-efi_ldflags = ['-T', efi_lds,
-               '-shared',
-               '-Bsymbolic',
-               '-nostdlib',
-               '--no-undefined',
-               '--warn-common',
-               '--fatal-warnings',
-               '-znocombreloc',
-               '--build-id=sha1',
-               '-L', efi_libdir,
-               efi_crt0]
+efi_ldflags = [
+        '-fuse-ld=' + get_option('efi-ld'),
+        '-L', efi_libdir,
+        '-nostdlib',
+        '-shared',
+        '-T', efi_lds,
+        '-Wl,--build-id=sha1',
+        '-Wl,--fatal-warnings',
+        '-Wl,--no-undefined',
+        '-Wl,--warn-common',
+        '-Wl,-Bsymbolic',
+        '-z', 'nocombreloc',
+        efi_crt0,
+]
 if efi_arch[1] in ['aarch64', 'arm', 'riscv64']
         # Aarch64, ARM32 and 64bit RISC-V don't have an EFI capable objcopy.
         # Use 'binary' instead, and add required symbols manually.
-        efi_ldflags += ['--defsym=EFI_SUBSYSTEM=0xa']
+        efi_ldflags += ['-Wl,--defsym=EFI_SUBSYSTEM=0xa']
         efi_format = ['-O', 'binary']
 else
         efi_format = ['--target=efi-app-@0@'.format(efi_arch[1])]
 endif
 
+if run_command('grep', '-q', '__CTOR_LIST__', efi_lds).returncode() == 0
+        # fedora has a patched gnu-efi that adds support for ELF constructors.
+        # If ld is called by gcc something about these symbols breaks, resulting
+        # in sd-boot freezing when gnu-efi runs the constructors. Force defining
+        # them seems to work around this.
+        efi_ldflags += [
+                '-Wl,--defsym=_init_array=0',
+                '-Wl,--defsym=_init_array_end=0',
+                '-Wl,--defsym=_fini_array=0',
+                '-Wl,--defsym=_fini_array_end=0',
+                '-Wl,--defsym=__CTOR_LIST__=0',
+                '-Wl,--defsym=__CTOR_END__=0',
+                '-Wl,--defsym=__DTOR_LIST__=0',
+                '-Wl,--defsym=__DTOR_END__=0',
+        ]
+endif
+
+efi_cc_version = run_command(efi_cc, '--version').stdout().split('\n')[0]
+if efi_cc_version.contains('clang') and efi_cc_version.split('.')[0].split(' ')[-1].to_int() <= 10
+        # clang <= 10 doesn't pass -T to the linker and then even complains about it being unused
+        efi_ldflags += ['-Wl,-T,' + efi_lds, '-Wno-unused-command-line-argument']
+endif
+
 systemd_boot_objects = []
 stub_objects = []
 foreach file : fundamental_source_paths + common_sources + systemd_boot_sources + stub_sources
@@ -308,7 +326,7 @@ foreach tuple : [['systemd_boot.so', systemd_boot_efi_name, systemd_boot_objects
                 tuple[0],
                 input : tuple[2],
                 output : tuple[0],
-                command : [efi_ld, '-o', '@OUTPUT@', efi_ldflags, tuple[2], '-lefi', '-lgnuefi', libgcc_file_name],
+                command : [efi_cc, '-o', '@OUTPUT@', efi_ldflags, tuple[2], '-lefi', '-lgnuefi', libgcc_file_name],
                 install : tuple[3],
                 install_dir : bootlibdir)