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Auto merge of #105812 - ojeda:no-jump-tables, r=nikic

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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
This commit is contained in:
bors 2022-12-21 17:38:38 +00:00
commit a8207df49e
6 changed files with 69 additions and 0 deletions
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9
compiler/rustc_codegen_llvm/src/attributes.rs
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@ -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));