From a65ec44779ab2c01ba937b40496ca648626d0308 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Sat, 17 Dec 2022 02:50:08 +0100 Subject: Add `-Zno-jump-tables` This flag mimics GCC/Clang's `-fno-jump-tables` [1][2], which makes the codegen backend avoid generating jump tables when lowering switches. In the case of LLVM, the `"no-jump-tables"="true"` function attribute is added to every function. The kernel currently needs it for x86 when enabling IBT [3], as well as for Alpha (plus VDSO objects in MIPS/LoongArch). [1] https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html#index-fno-jump-tables [2] https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-fjump-tables [3] https://github.com/torvalds/linux/blob/v6.1/arch/x86/Makefile#L75-L83 Signed-off-by: Miguel Ojeda --- compiler/rustc_codegen_llvm/src/attributes.rs | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'compiler/rustc_codegen_llvm/src') diff --git a/compiler/rustc_codegen_llvm/src/attributes.rs b/compiler/rustc_codegen_llvm/src/attributes.rs index f3bdacf6085..487eead22b8 100644 --- a/compiler/rustc_codegen_llvm/src/attributes.rs +++ b/compiler/rustc_codegen_llvm/src/attributes.rs @@ -137,6 +137,14 @@ fn instrument_function_attr<'ll>(cx: &CodegenCx<'ll, '_>) -> Option<&'ll Attribu } } +fn nojumptables_attr<'ll>(cx: &CodegenCx<'ll, '_>) -> Option<&'ll Attribute> { + if !cx.sess().opts.unstable_opts.no_jump_tables { + return None; + } + + Some(llvm::CreateAttrStringValue(cx.llcx, "no-jump-tables", "true")) +} + fn probestack_attr<'ll>(cx: &CodegenCx<'ll, '_>) -> Option<&'ll Attribute> { // Currently stack probes seem somewhat incompatible with the address // sanitizer and thread sanitizer. With asan we're already protected from @@ -293,6 +301,7 @@ pub fn from_fn_attrs<'ll, 'tcx>( // FIXME: none of these three functions interact with source level attributes. to_add.extend(frame_pointer_type_attr(cx)); to_add.extend(instrument_function_attr(cx)); + to_add.extend(nojumptables_attr(cx)); to_add.extend(probestack_attr(cx)); to_add.extend(stackprotector_attr(cx)); -- cgit 1.4.1-3-g733a5