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Rollup merge of #70095 - jsgf:link-native, r=nagisa
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Implement -Zlink-native-libraries

This implements a flag `-Zlink-native-libraries=yes/no`. If set to true/yes, or unspecified, then
native libraries referenced via `#[link]` attributes will be put on the linker line (ie, unchanged
behaviour).

If `-Zlink-native-libraries=no` is specified then rustc will not add the native libraries to the link
line. The assumption is that the outer build system driving the build already knows about the native
libraries and will specify them to the linker directly (for example via `-Clink-arg=`).

Addresses issue #70093
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Centril authored Mar 19, 2020
2 parents cde3df2 + bb55741 commit 89dbdc7
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Showing 3 changed files with 19 additions and 3 deletions.
13 changes: 10 additions & 3 deletions src/librustc_codegen_ssa/back/link.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1380,10 +1380,17 @@ fn link_args<'a, B: ArchiveBuilder<'a>>(
// link line. And finally upstream native libraries can't depend on anything
// in this DAG so far because they're only dylibs and dylibs can only depend
// on other dylibs (e.g., other native deps).
add_local_native_libraries(cmd, sess, codegen_results);
//
// If -Zlink-native-libraries=false is set, then the assumption is that an
// external build system already has the native dependencies defined, and it
// will provide them to the linker itself.
if sess.opts.debugging_opts.link_native_libraries.unwrap_or(true) {
add_local_native_libraries(cmd, sess, codegen_results);
}
add_upstream_rust_crates::<B>(cmd, sess, codegen_results, crate_type, tmpdir);
add_upstream_native_libraries(cmd, sess, codegen_results, crate_type);

if sess.opts.debugging_opts.link_native_libraries.unwrap_or(true) {
add_upstream_native_libraries(cmd, sess, codegen_results, crate_type);
}
// Tell the linker what we're doing.
if crate_type != config::CrateType::Executable {
cmd.build_dylib(out_filename);
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2 changes: 2 additions & 0 deletions src/librustc_session/options.rs
Original file line number Diff line number Diff line change
Expand Up @@ -968,4 +968,6 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
"link the `.rlink` file generated by `-Z no-link`"),
new_llvm_pass_manager: Option<bool> = (None, parse_opt_bool, [TRACKED],
"use new LLVM pass manager"),
link_native_libraries: Option<bool> = (None, parse_opt_bool, [UNTRACKED],
"Link native libraries in the linker invocation."),
}
7 changes: 7 additions & 0 deletions src/test/ui/issues/issue-70093.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
// run-pass
// compile-flags: -Zlink-native-libraries=no -Cdefault-linker-libraries=yes

#[link(name = "some-random-non-existent-library", kind = "static")]
extern "C" {}

fn main() {}

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