rust: add start-group/end-group arguments for libraries

rustc tries to use lld to link Rust programs, via the -fuse-ld=lld flag
to gcc or clang.  However, when absent it will use the GNU linker.
While lld seems to be adding --start-group/--end-group, ld.bfd can fail
if these options are needed.  This can cause difference between distros
depending on how Rust is packaged (e.g. Ubuntu 22.04 and Debian bookworm
seem to use ld.bfd).  To improve compatibility, add --start-group and
--end-group options like Meson already does with C programs.

The code is slightly different due to the rustc-specific "--emit" and
"--extern" options, therefore it's not really possible to share it
with the C-like compiler mixin.

Signed-off-by: Paolo Bonzini <[email protected]>

mesonbuild/compilers/rust.py

@@ -9,10 +9,13 @@
 import re
 import typing as T
 
+from .. import arglist
 from .. import options
+from ..linkers.linkers import GnuLikeDynamicLinkerMixin, SolarisDynamicLinker, CompCertDynamicLinker
 from ..mesonlib import EnvironmentException, MesonException, Popen_safe_logged
 from ..options import OptionKey
 from .compilers import Compiler, clike_debug_args
+from .mixins.clike import GROUP_FLAGS
 
 if T.TYPE_CHECKING:
     from ..coredata import MutableKeyedOptionDictType, KeyedOptionDictType
@@ -62,6 +65,35 @@ def get_rustup_run_and_args(exelist: T.List[str]) -> T.Optional[T.Tuple[T.List[s
     except StopIteration:
         return None
 
+
+class RustcCompilerArgs(arglist.CompilerArgs):
+    def to_native_inplace(self):
+        # Check if we need to add --start/end-group for circular dependencies
+        # between static libraries, and for recursively searching for symbols
+        # needed by static libraries that are provided by object files or
+        # shared libraries.
+        # This covers all ld.bfd, ld.gold, ld.gold, and xild on Linux, which
+        # all act like (or are) gnu ld
+        if isinstance(self.compiler.linker, (GnuLikeDynamicLinkerMixin, SolarisDynamicLinker, CompCertDynamicLinker)):
+            group_start = -1
+            group_end = -1
+            last_rustc_arg = -1
+            for i, each in enumerate(self):
+                if each in {'--emit', '-o', '--extern'}:
+                    last_rustc_arg = i
+                if last_rustc_arg == i - 1 or not GROUP_FLAGS.search(each):
+                    continue
+                group_end = i
+                if group_start < 0:
+                    # First occurrence of a library
+                    group_start = i
+            # Only add groups if there are multiple libraries.
+            if group_end > group_start >= 0:
+                # Last occurrence of a library
+                self.insert(group_end + 1, '-Clink-arg=-Wl,--end-group')
+                self.insert(group_start, '-Clink-arg=-Wl,--start-group')
+
+
 class RustCompiler(Compiler):
 
     # rustc doesn't invoke the compiler itself, it doesn't need a LINKER_PREFIX
@@ -100,6 +132,10 @@ def __init__(self, exelist: T.List[str], version: str, for_machine: MachineChoic
             self.base_options.add(OptionKey('b_vscrt'))
         self.native_static_libs: T.List[str] = []
 
+    def compiler_args(self, args: T.Optional[T.Iterable[str]] = None) -> RustcCompilerArgs:
+        # This is correct, mypy just doesn't understand co-operative inheritance
+        return RustcCompilerArgs(self, args)
+
     def needs_static_linker(self) -> bool:
         return False
 

test cases/rust/27 staticlib group/lib1.c

@@ -0,0 +1,11 @@
+#include <stdio.h>
+#include "lib1.h"
+#include "lib2.h"
+
+void from_lib2(void) {
+    printf("hello world");
+}
+
+void c_func(void) {
+    from_lib1();
+}

test cases/rust/27 staticlib group/lib1.h

@@ -0,0 +1,4 @@
+#pragma once
+
+void from_lib2(void);
+void c_func(void);

test cases/rust/27 staticlib group/lib2.c

@@ -0,0 +1,8 @@
+#include <stdio.h>
+#include "lib1.h"
+#include "lib2.h"
+
+void from_lib1(void)
+{
+    from_lib2();
+}

test cases/rust/27 staticlib group/lib2.h

@@ -0,0 +1,3 @@
+#pragma once
+
+void from_lib1(void);

test cases/rust/27 staticlib group/main.c

@@ -0,0 +1,6 @@
+#include "lib1.h"
+#include "lib2.h"
+
+void main() {
+    c_func();
+}

test cases/rust/27 staticlib group/main.rs

@@ -0,0 +1,9 @@
+extern "C" {
+    fn c_func();
+}
+
+fn main() {
+    unsafe {
+        c_func();
+    }
+}

test cases/rust/27 staticlib group/meson.build

@@ -0,0 +1,13 @@
+project('staticlib group', 'c', 'rust')
+
+ld_bfd = find_program('ld.bfd')
+if not ld_bfd.found()
+  error('MESON_SKIP_TEST ld.bfd not found')
+endif
+
+lib1 = static_library('lib1', 'lib1.c')
+lib2 = static_library('lib2', 'lib2.c')
+executable('lib1first', 'main.rs', link_with : [lib1, lib2],
+  rust_args: ['-C', 'lto=n', '-C', 'linker-plugin-lto=n', '-Clink-arg=-fuse-ld=bfd'])
+executable('lib2first', 'main.rs', link_with : [lib2, lib1],
+  rust_args: ['-C', 'lto=n', '-C', 'linker-plugin-lto=n', '-Clink-arg=-fuse-ld=bfd'])