Rollup merge of #140740 - ojeda:indirect-branch-cs-prefix, r=davidtwco

Add `-Zindirect-branch-cs-prefix`

Cc: ``@azhogin`` ``@Darksonn``

This goes on top of https://github.com/rust-lang/rust/pull/135927, i.e. please skip the first commit here. Please feel free to inherit it there.

In fact, I am not sure if there is any use case for the flag without `-Zretpoline*`. GCC and Clang allow it, though.

There is a `FIXME` for two `ignore`s in the test that I took from another test I did in the past -- they may be needed or not here since I didn't run the full CI. Either way, it is not critical.

Tracking issue: https://github.com/rust-lang/rust/issues/116852.
MCP: https://github.com/rust-lang/compiler-team/issues/868.

4 files changed, 70 insertions, 0 deletions

diff --git a/tests/assembly-llvm/x86_64-indirect-branch-cs-prefix.rs b/tests/assembly-llvm/x86_64-indirect-branch-cs-prefix.rs
new file mode 100644
index 00000000000..8e4470ee451
--- /dev/null
+++ b/tests/assembly-llvm/x86_64-indirect-branch-cs-prefix.rs
@@ -0,0 +1,27 @@
+// Test that the `cs` prefix is (not) added into a `call` and a `jmp` to the
+// indirect thunk when the `-Zindirect-branch-cs-prefix` flag is (not) set.
+
+//@ revisions: unset set
+//@ assembly-output: emit-asm
+//@ compile-flags: -Copt-level=3 -Cunsafe-allow-abi-mismatch=retpoline,retpoline-external-thunk,indirect-branch-cs-prefix -Zretpoline-external-thunk
+//@ [set] compile-flags: -Zindirect-branch-cs-prefix
+//@ only-x86_64
+//@ ignore-apple Symbol is called `___x86_indirect_thunk` (Darwin's extra underscore)
+
+#![crate_type = "lib"]
+
+// CHECK-LABEL: foo:
+#[no_mangle]
+pub fn foo(g: fn()) {
+    // unset-NOT: cs
+    // unset: callq {{__x86_indirect_thunk.*}}
+    // set: cs
+    // set-NEXT: callq {{__x86_indirect_thunk.*}}
+    g();
+
+    // unset-NOT: cs
+    // unset: jmp {{__x86_indirect_thunk.*}}
+    // set: cs
+    // set-NEXT: jmp {{__x86_indirect_thunk.*}}
+    g();
+}
diff --git a/tests/codegen-llvm/indirect-branch-cs-prefix.rs b/tests/codegen-llvm/indirect-branch-cs-prefix.rs
new file mode 100644
index 00000000000..df25008d5f0
--- /dev/null
+++ b/tests/codegen-llvm/indirect-branch-cs-prefix.rs
@@ -0,0 +1,18 @@
+// Test that the `indirect_branch_cs_prefix` module attribute is (not)
+// emitted when the `-Zindirect-branch-cs-prefix` flag is (not) set.
+
+//@ add-core-stubs
+//@ revisions: unset set
+//@ needs-llvm-components: x86
+//@ compile-flags: --target x86_64-unknown-linux-gnu
+//@ [set] compile-flags: -Zindirect-branch-cs-prefix
+
+#![crate_type = "lib"]
+#![feature(no_core, lang_items)]
+#![no_core]
+
+extern crate minicore;
+use minicore::*;
+
+// unset-NOT: !{{[0-9]+}} = !{i32 4, !"indirect_branch_cs_prefix", i32 1}
+// set: !{{[0-9]+}} = !{i32 4, !"indirect_branch_cs_prefix", i32 1}
diff --git a/tests/ui/invalid-compile-flags/indirect-branch-cs-prefix/requires-x86-or-x86_64.aarch64.stderr b/tests/ui/invalid-compile-flags/indirect-branch-cs-prefix/requires-x86-or-x86_64.aarch64.stderr
new file mode 100644
index 00000000000..e3f7871da35
--- /dev/null
+++ b/tests/ui/invalid-compile-flags/indirect-branch-cs-prefix/requires-x86-or-x86_64.aarch64.stderr
@@ -0,0 +1,4 @@
+error: `-Zindirect-branch-cs-prefix` is only supported on x86 and x86_64
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/invalid-compile-flags/indirect-branch-cs-prefix/requires-x86-or-x86_64.rs b/tests/ui/invalid-compile-flags/indirect-branch-cs-prefix/requires-x86-or-x86_64.rs
new file mode 100644
index 00000000000..bc81c993d26
--- /dev/null
+++ b/tests/ui/invalid-compile-flags/indirect-branch-cs-prefix/requires-x86-or-x86_64.rs
@@ -0,0 +1,21 @@
+//@ revisions: x86 x86_64 aarch64
+
+//@ compile-flags: -Zindirect-branch-cs-prefix
+
+//@[x86] check-pass
+//@[x86] needs-llvm-components: x86
+//@[x86] compile-flags: --target i686-unknown-linux-gnu
+
+//@[x86_64] check-pass
+//@[x86_64] needs-llvm-components: x86
+//@[x86_64] compile-flags: --target x86_64-unknown-linux-gnu
+
+//@[aarch64] check-fail
+//@[aarch64] needs-llvm-components: aarch64
+//@[aarch64] compile-flags: --target aarch64-unknown-linux-gnu
+
+#![feature(no_core)]
+#![no_core]
+#![no_main]
+
+//[aarch64]~? ERROR `-Zindirect-branch-cs-prefix` is only supported on x86 and x86_64