Rename -Zno-jump-tables to -Zjump-tables=<bool>

Both gcc and llvm accept -fjump-tables as well as -fno-jump-tables. For
consistency, allow rustc to accept -Zjump-tables=yes too.

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.no_jump_tables {
+    if cx.sess().opts.unstable_opts.jump_tables {
         return None;
     }
 

compiler/rustc_interface/src/tests.rs

@@ -813,6 +813,7 @@ 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);
@@ -830,7 +831,6 @@ fn test_unstable_options_tracking_hash() {
     tracked!(mutable_noalias, false);
     tracked!(next_solver, NextSolverConfig { coherence: true, globally: true });
     tracked!(no_generate_arange_section, true);
-    tracked!(no_jump_tables, true);
     tracked!(no_link, true);
     tracked!(no_profiler_runtime, true);
     tracked!(no_trait_vptr, true);

compiler/rustc_session/src/options.rs

@@ -2324,6 +2324,8 @@ 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],
@@ -2404,8 +2406,6 @@ options! {
         "omit DWARF address ranges that give faster lookups"),
     no_implied_bounds_compat: bool = (false, parse_bool, [TRACKED],
         "disable the compatibility version of the `implied_bounds_ty` query"),
-    no_jump_tables: bool = (false, parse_no_value, [TRACKED],
-        "disable the jump tables and lookup tables that can be generated from a switch case lowering"),
     no_leak_check: bool = (false, parse_no_value, [UNTRACKED],
         "disable the 'leak check' for subtyping; unsound, but useful for tests"),
     no_link: bool = (false, parse_no_value, [TRACKED],

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

@@ -0,0 +1,19 @@
+# `jump-tables`
+
+The tracking issue for this feature is [#116592](https://github.com/rust-lang/rust/issues/116592)
+
+---
+
+When set to no, this option enables the `-fno-jump-tables` flag for LLVM, which makes the
+codegen backend avoid generating jump tables when lowering switches.
+
+When set to no, this option adds the LLVM `no-jump-tables=true` attribute to every function.
+
+Disabling jump tables can be used to help provide protection against
+jump-oriented-programming (JOP) attacks, such as with the linux kernel's [IBT].
+
+```sh
+RUSTFLAGS="-Zjump-tables=no" cargo +nightly build -Z build-std
+```
+
+[IBT]: https://www.phoronix.com/news/Linux-IBT-By-Default-Tip

src/doc/unstable-book/src/compiler-flags/no-jump-tables.md

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

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

@@ -1,11 +1,12 @@
 // Test that the `no-jump-tables` function attribute are (not) emitted when
-// the `-Zno-jump-tables` flag is (not) set.
+// the `-Zjump-tables=no` flag is (not) set.
 
 //@ add-core-stubs
-//@ revisions: unset set
+//@ revisions: unset set_no set_yes
 //@ needs-llvm-components: x86
 //@ compile-flags: --target x86_64-unknown-linux-gnu
-//@ [set] compile-flags: -Zno-jump-tables
+//@ [set_no] compile-flags: -Zjump-tables=no
+//@ [set_yes] compile-flags: -Zjump-tables=yes
 
 #![crate_type = "lib"]
 #![feature(no_core, lang_items)]
@@ -19,5 +20,6 @@ pub fn foo() {
     // CHECK: @foo() unnamed_addr #0
 
     // unset-NOT: attributes #0 = { {{.*}}"no-jump-tables"="true"{{.*}} }
-    // set: attributes #0 = { {{.*}}"no-jump-tables"="true"{{.*}} }
+    // set_yes-NOT: attributes #0 = { {{.*}}"no-jump-tables"="true"{{.*}} }
+    // set_no: attributes #0 = { {{.*}}"no-jump-tables"="true"{{.*}} }
 }