Stabilize -Zjump-tables=<bool> into -Cjump-table=<bool>

Author: pmur

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -208,7 +208,7 @@ fn instrument_function_attr<'ll>(cx: &CodegenCx<'ll, '_>) -> SmallVec<[&'ll Attr
 }
 
 fn nojumptables_attr<'ll>(cx: &CodegenCx<'ll, '_>) -> Option<&'ll Attribute> {
-    if cx.sess().opts.unstable_opts.jump_tables {
+    if cx.sess().opts.cg.jump_tables {
         return None;
     }
 

compiler/rustc_interface/src/tests.rs

@@ -620,6 +620,7 @@ fn test_codegen_options_tracking_hash() {
     tracked!(force_frame_pointers, FramePointer::Always);
     tracked!(force_unwind_tables, Some(true));
     tracked!(instrument_coverage, InstrumentCoverage::Yes);
+    tracked!(jump_tables, false);
     tracked!(link_dead_code, Some(true));
     tracked!(linker_plugin_lto, LinkerPluginLto::LinkerPluginAuto);
     tracked!(llvm_args, vec![String::from("1"), String::from("2")]);
@@ -813,7 +814,6 @@ fn test_unstable_options_tracking_hash() {
     tracked!(inline_mir_threshold, Some(123));
     tracked!(instrument_mcount, true);
     tracked!(instrument_xray, Some(InstrumentXRay::default()));
-    tracked!(jump_tables, false);
     tracked!(link_directives, false);
     tracked!(link_only, true);
     tracked!(lint_llvm_ir, true);

compiler/rustc_session/src/options.rs

@@ -2022,6 +2022,8 @@ options! {
         "instrument the generated code to support LLVM source-based code coverage reports \
         (note, the compiler build config must include `profiler = true`); \
         implies `-C symbol-mangling-version=v0`"),
+    jump_tables: bool = (true, parse_bool, [TRACKED],
+        "Allow jump table and lookup table generation from switch case lowering (default: yes)"),
     link_arg: (/* redirected to link_args */) = ((), parse_string_push, [UNTRACKED],
         "a single extra argument to append to the linker invocation (can be used several times)"),
     link_args: Vec<String> = (Vec::new(), parse_list, [UNTRACKED],
@@ -2324,8 +2326,6 @@ options! {
          `=skip-entry`
          `=skip-exit`
          Multiple options can be combined with commas."),
-    jump_tables: bool = (true, parse_bool, [TRACKED],
-        "Allow jump table and lookup table generation from switch case lowering (default: yes)"),
     layout_seed: Option<u64> = (None, parse_opt_number, [TRACKED],
         "seed layout randomization"),
     link_directives: bool = (true, parse_bool, [TRACKED],

src/doc/rustc/src/codegen-options/index.md

@@ -209,6 +209,19 @@ Note that while the `-C instrument-coverage` option is stable, the profile data
 format produced by the resulting instrumentation may change, and may not work
 with coverage tools other than those built and shipped with the compiler.
 
+## jump-tables
+
+This option is used to allow or prevent the codegen backend from creating
+jump tables when lowering switches.
+
+* `y`, `yes`, `on`, `true` or no value: allow jump tables (the default).
+* `n`, `no`, `off` or `false`: disable jump tables.
+
+Disabling jump tables can be used to help provide protection against
+jump-oriented-programming (JOP) attacks, such as with the linux kernel's [IBT].
+
+[IBT]: https://www.phoronix.com/news/Linux-IBT-By-Default-Tip
+
 ## link-arg
 
 This flag lets you append a single extra argument to the linker invocation.

src/doc/unstable-book/src/compiler-flags/jump-tables.md

@@ -1,10 +1,10 @@
-// Test that jump tables are (not) emitted when the `-Zjump-tables=no`
+// Test that jump tables are (not) emitted when the `-Cjump-tables=no`
 // flag is (not) set.
 
 //@ revisions: unset set
 //@ assembly-output: emit-asm
 //@ compile-flags: -Copt-level=3
-//@ [set] compile-flags: -Zjump-tables=no
+//@ [set] compile-flags: -Cjump-tables=no
 //@ only-x86_64
 //@ ignore-sgx
 

tests/assembly-llvm/x86_64-no-jump-tables.rs

@@ -1,12 +1,12 @@
 // Test that the `no-jump-tables` function attribute are (not) emitted when
-// the `-Zjump-tables=no` flag is (not) set.
+// the `-Cjump-tables=no` flag is (not) set.
 
 //@ add-core-stubs
 //@ revisions: unset set_no set_yes
 //@ needs-llvm-components: x86
 //@ compile-flags: --target x86_64-unknown-linux-gnu
-//@ [set_no] compile-flags: -Zjump-tables=no
-//@ [set_yes] compile-flags: -Zjump-tables=yes
+//@ [set_no] compile-flags: -Cjump-tables=no
+//@ [set_yes] compile-flags: -Cjump-tables=yes
 
 #![crate_type = "lib"]
 #![feature(no_core, lang_items)]