1 //! Set and unset common attributes on LLVM values.
2
3 use std::ffi::CString;
4
5 use cstr::cstr;
6 use rustc_codegen_ssa::traits::*;
7 use rustc_data_structures::small_c_str::SmallCStr;
8 use rustc_hir::def_id::DefId;
9 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
10 use rustc_middle::ty::layout::HasTyCtxt;
11 use rustc_middle::ty::{self, TyCtxt};
12 use rustc_session::config::OptLevel;
13 use rustc_session::Session;
14 use rustc_target::spec::abi::Abi;
15 use rustc_target::spec::{FramePointer, SanitizerSet, StackProbeType, StackProtector};
16
17 use crate::attributes;
18 use crate::llvm::AttributePlace::Function;
19 use crate::llvm::{self, Attribute};
20 use crate::llvm_util;
21 pub use rustc_attr::{InlineAttr, InstructionSetAttr, OptimizeAttr};
22
23 use crate::context::CodegenCx;
24 use crate::value::Value;
25
26 /// Mark LLVM function to use provided inline heuristic.
27 #[inline]
inline(cx: &CodegenCx<'ll, '_>, val: &'ll Value, inline: InlineAttr)28 fn inline(cx: &CodegenCx<'ll, '_>, val: &'ll Value, inline: InlineAttr) {
29 use self::InlineAttr::*;
30 match inline {
31 Hint => Attribute::InlineHint.apply_llfn(Function, val),
32 Always => Attribute::AlwaysInline.apply_llfn(Function, val),
33 Never => {
34 if cx.tcx().sess.target.arch != "amdgpu" {
35 Attribute::NoInline.apply_llfn(Function, val);
36 }
37 }
38 None => {}
39 };
40 }
41
42 /// Apply LLVM sanitize attributes.
43 #[inline]
sanitize(cx: &CodegenCx<'ll, '_>, no_sanitize: SanitizerSet, llfn: &'ll Value)44 pub fn sanitize(cx: &CodegenCx<'ll, '_>, no_sanitize: SanitizerSet, llfn: &'ll Value) {
45 let enabled = cx.tcx.sess.opts.debugging_opts.sanitizer - no_sanitize;
46 if enabled.contains(SanitizerSet::ADDRESS) {
47 llvm::Attribute::SanitizeAddress.apply_llfn(Function, llfn);
48 }
49 if enabled.contains(SanitizerSet::MEMORY) {
50 llvm::Attribute::SanitizeMemory.apply_llfn(Function, llfn);
51 }
52 if enabled.contains(SanitizerSet::THREAD) {
53 llvm::Attribute::SanitizeThread.apply_llfn(Function, llfn);
54 }
55 if enabled.contains(SanitizerSet::HWADDRESS) {
56 llvm::Attribute::SanitizeHWAddress.apply_llfn(Function, llfn);
57 }
58 }
59
60 /// Tell LLVM to emit or not emit the information necessary to unwind the stack for the function.
61 #[inline]
emit_uwtable(val: &'ll Value, emit: bool)62 pub fn emit_uwtable(val: &'ll Value, emit: bool) {
63 Attribute::UWTable.toggle_llfn(Function, val, emit);
64 }
65
66 /// Tell LLVM if this function should be 'naked', i.e., skip the epilogue and prologue.
67 #[inline]
naked(val: &'ll Value, is_naked: bool)68 fn naked(val: &'ll Value, is_naked: bool) {
69 Attribute::Naked.toggle_llfn(Function, val, is_naked);
70 }
71
set_frame_pointer_type(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value)72 pub fn set_frame_pointer_type(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
73 let mut fp = cx.sess().target.frame_pointer;
74 // "mcount" function relies on stack pointer.
75 // See <https://sourceware.org/binutils/docs/gprof/Implementation.html>.
76 if cx.sess().instrument_mcount() || matches!(cx.sess().opts.cg.force_frame_pointers, Some(true))
77 {
78 fp = FramePointer::Always;
79 }
80 let attr_value = match fp {
81 FramePointer::Always => cstr!("all"),
82 FramePointer::NonLeaf => cstr!("non-leaf"),
83 FramePointer::MayOmit => return,
84 };
85 llvm::AddFunctionAttrStringValue(
86 llfn,
87 llvm::AttributePlace::Function,
88 cstr!("frame-pointer"),
89 attr_value,
90 );
91 }
92
93 /// Tell LLVM what instrument function to insert.
94 #[inline]
set_instrument_function(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value)95 fn set_instrument_function(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
96 if cx.sess().instrument_mcount() {
97 // Similar to `clang -pg` behavior. Handled by the
98 // `post-inline-ee-instrument` LLVM pass.
99
100 // The function name varies on platforms.
101 // See test/CodeGen/mcount.c in clang.
102 let mcount_name = CString::new(cx.sess().target.mcount.as_str().as_bytes()).unwrap();
103
104 llvm::AddFunctionAttrStringValue(
105 llfn,
106 llvm::AttributePlace::Function,
107 cstr!("instrument-function-entry-inlined"),
108 &mcount_name,
109 );
110 }
111 }
112
set_probestack(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value)113 fn set_probestack(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
114 // Currently stack probes seem somewhat incompatible with the address
115 // sanitizer and thread sanitizer. With asan we're already protected from
116 // stack overflow anyway so we don't really need stack probes regardless.
117 if cx
118 .sess()
119 .opts
120 .debugging_opts
121 .sanitizer
122 .intersects(SanitizerSet::ADDRESS | SanitizerSet::THREAD)
123 {
124 return;
125 }
126
127 // probestack doesn't play nice either with `-C profile-generate`.
128 if cx.sess().opts.cg.profile_generate.enabled() {
129 return;
130 }
131
132 // probestack doesn't play nice either with gcov profiling.
133 if cx.sess().opts.debugging_opts.profile {
134 return;
135 }
136
137 let attr_value = match cx.sess().target.stack_probes {
138 StackProbeType::None => None,
139 // Request LLVM to generate the probes inline. If the given LLVM version does not support
140 // this, no probe is generated at all (even if the attribute is specified).
141 StackProbeType::Inline => Some(cstr!("inline-asm")),
142 // Flag our internal `__rust_probestack` function as the stack probe symbol.
143 // This is defined in the `compiler-builtins` crate for each architecture.
144 StackProbeType::Call => Some(cstr!("__rust_probestack")),
145 // Pick from the two above based on the LLVM version.
146 StackProbeType::InlineOrCall { min_llvm_version_for_inline } => {
147 if llvm_util::get_version() < min_llvm_version_for_inline {
148 Some(cstr!("__rust_probestack"))
149 } else {
150 Some(cstr!("inline-asm"))
151 }
152 }
153 };
154 if let Some(attr_value) = attr_value {
155 llvm::AddFunctionAttrStringValue(
156 llfn,
157 llvm::AttributePlace::Function,
158 cstr!("probe-stack"),
159 attr_value,
160 );
161 }
162 }
163
set_stackprotector(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value)164 fn set_stackprotector(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
165 let sspattr = match cx.sess().stack_protector() {
166 StackProtector::None => return,
167 StackProtector::All => Attribute::StackProtectReq,
168 StackProtector::Strong => Attribute::StackProtectStrong,
169 StackProtector::Basic => Attribute::StackProtect,
170 };
171
172 sspattr.apply_llfn(Function, llfn)
173 }
174
apply_target_cpu_attr(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value)175 pub fn apply_target_cpu_attr(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
176 let target_cpu = SmallCStr::new(llvm_util::target_cpu(cx.tcx.sess));
177 llvm::AddFunctionAttrStringValue(
178 llfn,
179 llvm::AttributePlace::Function,
180 cstr!("target-cpu"),
181 target_cpu.as_c_str(),
182 );
183 }
184
apply_tune_cpu_attr(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value)185 pub fn apply_tune_cpu_attr(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
186 if let Some(tune) = llvm_util::tune_cpu(cx.tcx.sess) {
187 let tune_cpu = SmallCStr::new(tune);
188 llvm::AddFunctionAttrStringValue(
189 llfn,
190 llvm::AttributePlace::Function,
191 cstr!("tune-cpu"),
192 tune_cpu.as_c_str(),
193 );
194 }
195 }
196
197 /// Sets the `NonLazyBind` LLVM attribute on a given function,
198 /// assuming the codegen options allow skipping the PLT.
non_lazy_bind(sess: &Session, llfn: &'ll Value)199 pub fn non_lazy_bind(sess: &Session, llfn: &'ll Value) {
200 // Don't generate calls through PLT if it's not necessary
201 if !sess.needs_plt() {
202 Attribute::NonLazyBind.apply_llfn(Function, llfn);
203 }
204 }
205
default_optimisation_attrs(sess: &Session, llfn: &'ll Value)206 pub(crate) fn default_optimisation_attrs(sess: &Session, llfn: &'ll Value) {
207 match sess.opts.optimize {
208 OptLevel::Size => {
209 llvm::Attribute::MinSize.unapply_llfn(Function, llfn);
210 llvm::Attribute::OptimizeForSize.apply_llfn(Function, llfn);
211 llvm::Attribute::OptimizeNone.unapply_llfn(Function, llfn);
212 }
213 OptLevel::SizeMin => {
214 llvm::Attribute::MinSize.apply_llfn(Function, llfn);
215 llvm::Attribute::OptimizeForSize.apply_llfn(Function, llfn);
216 llvm::Attribute::OptimizeNone.unapply_llfn(Function, llfn);
217 }
218 OptLevel::No => {
219 llvm::Attribute::MinSize.unapply_llfn(Function, llfn);
220 llvm::Attribute::OptimizeForSize.unapply_llfn(Function, llfn);
221 llvm::Attribute::OptimizeNone.unapply_llfn(Function, llfn);
222 }
223 _ => {}
224 }
225 }
226
227 /// Composite function which sets LLVM attributes for function depending on its AST (`#[attribute]`)
228 /// attributes.
from_fn_attrs(cx: &CodegenCx<'ll, 'tcx>, llfn: &'ll Value, instance: ty::Instance<'tcx>)229 pub fn from_fn_attrs(cx: &CodegenCx<'ll, 'tcx>, llfn: &'ll Value, instance: ty::Instance<'tcx>) {
230 let codegen_fn_attrs = cx.tcx.codegen_fn_attrs(instance.def_id());
231
232 match codegen_fn_attrs.optimize {
233 OptimizeAttr::None => {
234 default_optimisation_attrs(cx.tcx.sess, llfn);
235 }
236 OptimizeAttr::Speed => {
237 llvm::Attribute::MinSize.unapply_llfn(Function, llfn);
238 llvm::Attribute::OptimizeForSize.unapply_llfn(Function, llfn);
239 llvm::Attribute::OptimizeNone.unapply_llfn(Function, llfn);
240 }
241 OptimizeAttr::Size => {
242 llvm::Attribute::MinSize.apply_llfn(Function, llfn);
243 llvm::Attribute::OptimizeForSize.apply_llfn(Function, llfn);
244 llvm::Attribute::OptimizeNone.unapply_llfn(Function, llfn);
245 }
246 }
247
248 let inline_attr = if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
249 InlineAttr::Never
250 } else if codegen_fn_attrs.inline == InlineAttr::None && instance.def.requires_inline(cx.tcx) {
251 InlineAttr::Hint
252 } else {
253 codegen_fn_attrs.inline
254 };
255 inline(cx, llfn, inline_attr);
256
257 // The `uwtable` attribute according to LLVM is:
258 //
259 // This attribute indicates that the ABI being targeted requires that an
260 // unwind table entry be produced for this function even if we can show
261 // that no exceptions passes by it. This is normally the case for the
262 // ELF x86-64 abi, but it can be disabled for some compilation units.
263 //
264 // Typically when we're compiling with `-C panic=abort` (which implies this
265 // `no_landing_pads` check) we don't need `uwtable` because we can't
266 // generate any exceptions! On Windows, however, exceptions include other
267 // events such as illegal instructions, segfaults, etc. This means that on
268 // Windows we end up still needing the `uwtable` attribute even if the `-C
269 // panic=abort` flag is passed.
270 //
271 // You can also find more info on why Windows always requires uwtables here:
272 // https://bugzilla.mozilla.org/show_bug.cgi?id=1302078
273 if cx.sess().must_emit_unwind_tables() {
274 attributes::emit_uwtable(llfn, true);
275 }
276
277 if cx.sess().opts.debugging_opts.profile_sample_use.is_some() {
278 llvm::AddFunctionAttrString(llfn, Function, cstr!("use-sample-profile"));
279 }
280
281 // FIXME: none of these three functions interact with source level attributes.
282 set_frame_pointer_type(cx, llfn);
283 set_instrument_function(cx, llfn);
284 set_probestack(cx, llfn);
285 set_stackprotector(cx, llfn);
286
287 if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
288 Attribute::Cold.apply_llfn(Function, llfn);
289 }
290 if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::FFI_RETURNS_TWICE) {
291 Attribute::ReturnsTwice.apply_llfn(Function, llfn);
292 }
293 if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::FFI_PURE) {
294 Attribute::ReadOnly.apply_llfn(Function, llfn);
295 }
296 if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::FFI_CONST) {
297 Attribute::ReadNone.apply_llfn(Function, llfn);
298 }
299 if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
300 naked(llfn, true);
301 }
302 if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::ALLOCATOR) {
303 Attribute::NoAlias.apply_llfn(llvm::AttributePlace::ReturnValue, llfn);
304 }
305 if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::CMSE_NONSECURE_ENTRY) {
306 llvm::AddFunctionAttrString(llfn, Function, cstr!("cmse_nonsecure_entry"));
307 }
308 if let Some(align) = codegen_fn_attrs.alignment {
309 llvm::set_alignment(llfn, align as usize);
310 }
311 sanitize(cx, codegen_fn_attrs.no_sanitize, llfn);
312
313 // Always annotate functions with the target-cpu they are compiled for.
314 // Without this, ThinLTO won't inline Rust functions into Clang generated
315 // functions (because Clang annotates functions this way too).
316 apply_target_cpu_attr(cx, llfn);
317 // tune-cpu is only conveyed through the attribute for our purpose.
318 // The target doesn't care; the subtarget reads our attribute.
319 apply_tune_cpu_attr(cx, llfn);
320
321 let mut function_features = codegen_fn_attrs
322 .target_features
323 .iter()
324 .flat_map(|f| {
325 let feature = &f.as_str();
326 llvm_util::to_llvm_feature(cx.tcx.sess, feature)
327 .into_iter()
328 .map(|f| format!("+{}", f))
329 .collect::<Vec<String>>()
330 })
331 .chain(codegen_fn_attrs.instruction_set.iter().map(|x| match x {
332 InstructionSetAttr::ArmA32 => "-thumb-mode".to_string(),
333 InstructionSetAttr::ArmT32 => "+thumb-mode".to_string(),
334 }))
335 .collect::<Vec<String>>();
336
337 if cx.tcx.sess.target.is_like_wasm {
338 // If this function is an import from the environment but the wasm
339 // import has a specific module/name, apply them here.
340 if let Some(module) = wasm_import_module(cx.tcx, instance.def_id()) {
341 llvm::AddFunctionAttrStringValue(
342 llfn,
343 llvm::AttributePlace::Function,
344 cstr!("wasm-import-module"),
345 &module,
346 );
347
348 let name =
349 codegen_fn_attrs.link_name.unwrap_or_else(|| cx.tcx.item_name(instance.def_id()));
350 let name = CString::new(&name.as_str()[..]).unwrap();
351 llvm::AddFunctionAttrStringValue(
352 llfn,
353 llvm::AttributePlace::Function,
354 cstr!("wasm-import-name"),
355 &name,
356 );
357 }
358
359 // The `"wasm"` abi on wasm targets automatically enables the
360 // `+multivalue` feature because the purpose of the wasm abi is to match
361 // the WebAssembly specification, which has this feature. This won't be
362 // needed when LLVM enables this `multivalue` feature by default.
363 if !cx.tcx.is_closure(instance.def_id()) {
364 let abi = cx.tcx.fn_sig(instance.def_id()).abi();
365 if abi == Abi::Wasm {
366 function_features.push("+multivalue".to_string());
367 }
368 }
369 }
370
371 if !function_features.is_empty() {
372 let mut global_features = llvm_util::llvm_global_features(cx.tcx.sess);
373 global_features.extend(function_features.into_iter());
374 let features = global_features.join(",");
375 let val = CString::new(features).unwrap();
376 llvm::AddFunctionAttrStringValue(
377 llfn,
378 llvm::AttributePlace::Function,
379 cstr!("target-features"),
380 &val,
381 );
382 }
383 }
384
wasm_import_module(tcx: TyCtxt<'_>, id: DefId) -> Option<CString>385 fn wasm_import_module(tcx: TyCtxt<'_>, id: DefId) -> Option<CString> {
386 tcx.wasm_import_module_map(id.krate).get(&id).map(|s| CString::new(&s[..]).unwrap())
387 }
388