[PATCH 2/2] meson: let Meson handle mixed-language linking of Rust and C objects

[Paolo Bonzini <pbonzini@redhat.com>]

Meson 1.9.0 can pass C objects into rustc so that the final link pass can
add the Rust libstd.  Use that to eliminate the staticlib and allow
dynamic linking with libstd (also introduced by Meson 1.9.0, but not
for staticlib crates due to lack of support in rustc).

The main() function is still provided by C, which is possible by
declaring the main source file of the Rust executable (which is
created by scripts/rust/rust_root_crate.sh) as #![no_main].

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 meson.build                     | 19 ++++++++-----------
 scripts/rust/rust_root_crate.sh |  1 +
 2 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/meson.build b/meson.build
index e53cd5b4138..0a921272f57 100644
--- a/meson.build
+++ b/meson.build
@@ -4377,25 +4377,22 @@ foreach target : target_dirs
   arch_srcs += target_specific.sources()
   arch_deps += target_specific.dependencies()
 
+  main_rs = []
+  crates = []
   if have_rust and target_type == 'system'
     target_rust = rust_devices_ss.apply(config_target, strict: false)
-    crates = []
+    arch_deps += target_rust.dependencies()
     foreach dep : target_rust.dependencies()
       crates += dep.get_variable('crate')
     endforeach
     if crates.length() > 0
-      rlib_rs = custom_target('rust_' + target.underscorify() + '.rs',
+      main_rs = custom_target('rust_' + target.underscorify() + '.rs',
                               output: 'rust_' + target.underscorify() + '.rs',
                               command: [rust_root_crate, crates],
                               capture: true,
                               build_by_default: true,
                               build_always_stale: true)
-      rlib = static_library('rust_' + target.underscorify(),
-                            structured_sources([], {'.': rlib_rs}),
-                            dependencies: target_rust.dependencies(),
-                            override_options: ['rust_std=2021', 'build.rust_std=2021'],
-                            rust_abi: 'c')
-      arch_deps += declare_dependency(link_whole: [rlib])
+      main_rs = structured_sources(main_rs)
     endif
   endif
 
@@ -4419,14 +4416,14 @@ foreach target : target_dirs
     execs = [{
       'name': 'qemu-system-' + target_name,
       'win_subsystem': 'console',
-      'sources': files('system/main.c'),
+      'sources': [main_rs, files('system/main.c')],
       'dependencies': [sdl]
     }]
     if host_os == 'windows' and (sdl.found() or gtk.found())
       execs += [{
         'name': 'qemu-system-' + target_name + 'w',
         'win_subsystem': 'windows',
-        'sources': files('system/main.c'),
+        'sources': [main_rs, files('system/main.c')],
         'dependencies': [sdl]
       }]
     endif
@@ -4435,7 +4432,7 @@ foreach target : target_dirs
       execs += [{
         'name': 'qemu-fuzz-' + target_name,
         'win_subsystem': 'console',
-        'sources': specific_fuzz.sources(),
+        'sources': [main_rs, specific_fuzz.sources()],
         'dependencies': specific_fuzz.dependencies(),
       }]
     endif
diff --git a/scripts/rust/rust_root_crate.sh b/scripts/rust/rust_root_crate.sh
index 975bddf7f1a..1ee88114ad9 100755
--- a/scripts/rust/rust_root_crate.sh
+++ b/scripts/rust/rust_root_crate.sh
@@ -6,6 +6,7 @@ cat <<EOF
 // @generated
 // This file is autogenerated by scripts/rust_root_crate.sh
 
+#![no_main]
 EOF
 
 for crate in $*; do
-- 
2.50.1