rustc_codegen_llvm/
attributes.rs

1//! Set and unset common attributes on LLVM values.
2use rustc_hir::attrs::{InlineAttr, InstructionSetAttr, OptimizeAttr, RtsanSetting};
3use rustc_hir::def_id::DefId;
4use rustc_hir::find_attr;
5use rustc_middle::middle::codegen_fn_attrs::{
6    CodegenFnAttrFlags, CodegenFnAttrs, PatchableFunctionEntry, SanitizerFnAttrs, TargetFeature,
7};
8use rustc_middle::ty::{self, TyCtxt};
9use rustc_session::config::{BranchProtection, FunctionReturn, OptLevel, PAuthKey, PacRet};
10use rustc_span::sym;
11use rustc_symbol_mangling::mangle_internal_symbol;
12use rustc_target::spec::{Arch, FramePointer, SanitizerSet, StackProbeType, StackProtector};
13use smallvec::SmallVec;
14
15use crate::context::SimpleCx;
16use crate::errors::{PackedStackBackchainNeedsSoftfloat, SanitizerMemtagRequiresMte};
17use crate::llvm::AttributePlace::Function;
18use crate::llvm::{
19    self, AllocKindFlags, Attribute, AttributeKind, AttributePlace, MemoryEffects, Value,
20};
21use crate::{Session, attributes, llvm_util};
22
23pub(crate) fn apply_to_llfn(llfn: &Value, idx: AttributePlace, attrs: &[&Attribute]) {
24    if !attrs.is_empty() {
25        llvm::AddFunctionAttributes(llfn, idx, attrs);
26    }
27}
28
29pub(crate) fn apply_to_callsite(callsite: &Value, idx: AttributePlace, attrs: &[&Attribute]) {
30    if !attrs.is_empty() {
31        llvm::AddCallSiteAttributes(callsite, idx, attrs);
32    }
33}
34
35pub(crate) fn has_string_attr(llfn: &Value, name: &str) -> bool {
36    llvm::HasStringAttribute(llfn, name)
37}
38
39pub(crate) fn remove_string_attr_from_llfn(llfn: &Value, name: &str) {
40    llvm::RemoveStringAttrFromFn(llfn, name);
41}
42
43/// Get LLVM attribute for the provided inline heuristic.
44#[inline]
45fn inline_attr<'ll>(
46    cx: &SimpleCx<'ll>,
47    sess: &Session,
48    inline: InlineAttr,
49) -> Option<&'ll Attribute> {
50    if !sess.opts.unstable_opts.inline_llvm {
51        // disable LLVM inlining
52        return Some(AttributeKind::NoInline.create_attr(cx.llcx));
53    }
54    match inline {
55        InlineAttr::Hint => Some(AttributeKind::InlineHint.create_attr(cx.llcx)),
56        InlineAttr::Always | InlineAttr::Force { .. } => {
57            Some(AttributeKind::AlwaysInline.create_attr(cx.llcx))
58        }
59        InlineAttr::Never => {
60            if sess.target.arch != Arch::AmdGpu {
61                Some(AttributeKind::NoInline.create_attr(cx.llcx))
62            } else {
63                None
64            }
65        }
66        InlineAttr::None => None,
67    }
68}
69
70#[inline]
71fn patchable_function_entry_attrs<'ll>(
72    cx: &SimpleCx<'ll>,
73    sess: &Session,
74    attr: Option<PatchableFunctionEntry>,
75) -> SmallVec<[&'ll Attribute; 2]> {
76    let mut attrs = SmallVec::new();
77    let patchable_spec = attr.unwrap_or_else(|| {
78        PatchableFunctionEntry::from_config(sess.opts.unstable_opts.patchable_function_entry)
79    });
80    let entry = patchable_spec.entry();
81    let prefix = patchable_spec.prefix();
82    if entry > 0 {
83        attrs.push(llvm::CreateAttrStringValue(
84            cx.llcx,
85            "patchable-function-entry",
86            &::alloc::__export::must_use({
        ::alloc::fmt::format(format_args!("{0}", entry))
    })format!("{}", entry),
87        ));
88    }
89    if prefix > 0 {
90        attrs.push(llvm::CreateAttrStringValue(
91            cx.llcx,
92            "patchable-function-prefix",
93            &::alloc::__export::must_use({
        ::alloc::fmt::format(format_args!("{0}", prefix))
    })format!("{}", prefix),
94        ));
95    }
96    attrs
97}
98
99/// Get LLVM sanitize attributes.
100#[inline]
101pub(crate) fn sanitize_attrs<'ll, 'tcx>(
102    cx: &SimpleCx<'ll>,
103    tcx: TyCtxt<'tcx>,
104    sanitizer_fn_attr: SanitizerFnAttrs,
105) -> SmallVec<[&'ll Attribute; 4]> {
106    let mut attrs = SmallVec::new();
107    let enabled = tcx.sess.sanitizers() - sanitizer_fn_attr.disabled;
108    if enabled.contains(SanitizerSet::ADDRESS) || enabled.contains(SanitizerSet::KERNELADDRESS) {
109        attrs.push(llvm::AttributeKind::SanitizeAddress.create_attr(cx.llcx));
110    }
111    if enabled.contains(SanitizerSet::MEMORY) {
112        attrs.push(llvm::AttributeKind::SanitizeMemory.create_attr(cx.llcx));
113    }
114    if enabled.contains(SanitizerSet::THREAD) {
115        attrs.push(llvm::AttributeKind::SanitizeThread.create_attr(cx.llcx));
116    }
117    if enabled.contains(SanitizerSet::HWADDRESS) || enabled.contains(SanitizerSet::KERNELHWADDRESS)
118    {
119        attrs.push(llvm::AttributeKind::SanitizeHWAddress.create_attr(cx.llcx));
120    }
121    if enabled.contains(SanitizerSet::SHADOWCALLSTACK) {
122        attrs.push(llvm::AttributeKind::ShadowCallStack.create_attr(cx.llcx));
123    }
124    if enabled.contains(SanitizerSet::MEMTAG) {
125        // Check to make sure the mte target feature is actually enabled.
126        let features = tcx.global_backend_features(());
127        let mte_feature =
128            features.iter().map(|s| &s[..]).rfind(|n| ["+mte", "-mte"].contains(&&n[..]));
129        if let None | Some("-mte") = mte_feature {
130            tcx.dcx().emit_err(SanitizerMemtagRequiresMte);
131        }
132
133        attrs.push(llvm::AttributeKind::SanitizeMemTag.create_attr(cx.llcx));
134    }
135    if enabled.contains(SanitizerSet::SAFESTACK) {
136        attrs.push(llvm::AttributeKind::SanitizeSafeStack.create_attr(cx.llcx));
137    }
138    if tcx.sess.sanitizers().contains(SanitizerSet::REALTIME) {
139        match sanitizer_fn_attr.rtsan_setting {
140            RtsanSetting::Nonblocking => {
141                attrs.push(llvm::AttributeKind::SanitizeRealtimeNonblocking.create_attr(cx.llcx))
142            }
143            RtsanSetting::Blocking => {
144                attrs.push(llvm::AttributeKind::SanitizeRealtimeBlocking.create_attr(cx.llcx))
145            }
146            // caller is the default, so no llvm attribute
147            RtsanSetting::Caller => (),
148        }
149    }
150    attrs
151}
152
153/// Tell LLVM to emit or not emit the information necessary to unwind the stack for the function.
154#[inline]
155pub(crate) fn uwtable_attr(llcx: &llvm::Context, use_sync_unwind: Option<bool>) -> &Attribute {
156    // NOTE: We should determine if we even need async unwind tables, as they
157    // take have more overhead and if we can use sync unwind tables we
158    // probably should.
159    let async_unwind = !use_sync_unwind.unwrap_or(false);
160    llvm::CreateUWTableAttr(llcx, async_unwind)
161}
162
163pub(crate) fn frame_pointer_type_attr<'ll>(
164    cx: &SimpleCx<'ll>,
165    sess: &Session,
166) -> Option<&'ll Attribute> {
167    let mut fp = sess.target.frame_pointer;
168    let opts = &sess.opts;
169    // "mcount" function relies on stack pointer.
170    // See <https://sourceware.org/binutils/docs/gprof/Implementation.html>.
171    if opts.unstable_opts.instrument_mcount {
172        fp.ratchet(FramePointer::Always);
173    }
174    fp.ratchet(opts.cg.force_frame_pointers);
175    let attr_value = match fp {
176        FramePointer::Always => "all",
177        FramePointer::NonLeaf => "non-leaf",
178        FramePointer::MayOmit => return None,
179    };
180    Some(llvm::CreateAttrStringValue(cx.llcx, "frame-pointer", attr_value))
181}
182
183fn function_return_attr<'ll>(cx: &SimpleCx<'ll>, sess: &Session) -> Option<&'ll Attribute> {
184    let function_return_attr = match sess.opts.unstable_opts.function_return {
185        FunctionReturn::Keep => return None,
186        FunctionReturn::ThunkExtern => AttributeKind::FnRetThunkExtern,
187    };
188
189    Some(function_return_attr.create_attr(cx.llcx))
190}
191
192/// Tell LLVM what instrument function to insert.
193#[inline]
194fn instrument_function_attr<'ll>(
195    cx: &SimpleCx<'ll>,
196    sess: &Session,
197) -> SmallVec<[&'ll Attribute; 4]> {
198    let mut attrs = SmallVec::new();
199    if sess.opts.unstable_opts.instrument_mcount {
200        // Similar to `clang -pg` behavior. Handled by the
201        // `post-inline-ee-instrument` LLVM pass.
202
203        // The function name varies on platforms.
204        // See test/CodeGen/mcount.c in clang.
205        let mcount_name = match &sess.target.llvm_mcount_intrinsic {
206            Some(llvm_mcount_intrinsic) => llvm_mcount_intrinsic.as_ref(),
207            None => sess.target.mcount.as_ref(),
208        };
209
210        attrs.push(llvm::CreateAttrStringValue(
211            cx.llcx,
212            "instrument-function-entry-inlined",
213            mcount_name,
214        ));
215    }
216    if let Some(options) = &sess.opts.unstable_opts.instrument_xray {
217        // XRay instrumentation is similar to __cyg_profile_func_{enter,exit}.
218        // Function prologue and epilogue are instrumented with NOP sleds,
219        // a runtime library later replaces them with detours into tracing code.
220        if options.always {
221            attrs.push(llvm::CreateAttrStringValue(cx.llcx, "function-instrument", "xray-always"));
222        }
223        if options.never {
224            attrs.push(llvm::CreateAttrStringValue(cx.llcx, "function-instrument", "xray-never"));
225        }
226        if options.ignore_loops {
227            attrs.push(llvm::CreateAttrString(cx.llcx, "xray-ignore-loops"));
228        }
229        // LLVM will not choose the default for us, but rather requires specific
230        // threshold in absence of "xray-always". Use the same default as Clang.
231        let threshold = options.instruction_threshold.unwrap_or(200);
232        attrs.push(llvm::CreateAttrStringValue(
233            cx.llcx,
234            "xray-instruction-threshold",
235            &threshold.to_string(),
236        ));
237        if options.skip_entry {
238            attrs.push(llvm::CreateAttrString(cx.llcx, "xray-skip-entry"));
239        }
240        if options.skip_exit {
241            attrs.push(llvm::CreateAttrString(cx.llcx, "xray-skip-exit"));
242        }
243    }
244    attrs
245}
246
247fn nojumptables_attr<'ll>(cx: &SimpleCx<'ll>, sess: &Session) -> Option<&'ll Attribute> {
248    if sess.opts.cg.jump_tables {
249        return None;
250    }
251
252    Some(llvm::CreateAttrStringValue(cx.llcx, "no-jump-tables", "true"))
253}
254
255fn probestack_attr<'ll, 'tcx>(cx: &SimpleCx<'ll>, tcx: TyCtxt<'tcx>) -> Option<&'ll Attribute> {
256    // Currently stack probes seem somewhat incompatible with the address
257    // sanitizer and thread sanitizer. With asan we're already protected from
258    // stack overflow anyway so we don't really need stack probes regardless.
259    if tcx.sess.sanitizers().intersects(SanitizerSet::ADDRESS | SanitizerSet::THREAD) {
260        return None;
261    }
262
263    // probestack doesn't play nice either with `-C profile-generate`.
264    if tcx.sess.opts.cg.profile_generate.enabled() {
265        return None;
266    }
267
268    let attr_value = match tcx.sess.target.stack_probes {
269        StackProbeType::None => return None,
270        // Request LLVM to generate the probes inline. If the given LLVM version does not support
271        // this, no probe is generated at all (even if the attribute is specified).
272        StackProbeType::Inline => "inline-asm",
273        // Flag our internal `__rust_probestack` function as the stack probe symbol.
274        // This is defined in the `compiler-builtins` crate for each architecture.
275        StackProbeType::Call => &mangle_internal_symbol(tcx, "__rust_probestack"),
276        // Pick from the two above based on the LLVM version.
277        StackProbeType::InlineOrCall { min_llvm_version_for_inline } => {
278            if llvm_util::get_version() < min_llvm_version_for_inline {
279                &mangle_internal_symbol(tcx, "__rust_probestack")
280            } else {
281                "inline-asm"
282            }
283        }
284    };
285    Some(llvm::CreateAttrStringValue(cx.llcx, "probe-stack", attr_value))
286}
287
288fn stackprotector_attr<'ll>(cx: &SimpleCx<'ll>, sess: &Session) -> Option<&'ll Attribute> {
289    let sspattr = match sess.stack_protector() {
290        StackProtector::None => return None,
291        StackProtector::All => AttributeKind::StackProtectReq,
292        StackProtector::Strong => AttributeKind::StackProtectStrong,
293        StackProtector::Basic => AttributeKind::StackProtect,
294    };
295
296    Some(sspattr.create_attr(cx.llcx))
297}
298
299fn packed_stack_attr<'ll>(
300    cx: &SimpleCx<'ll>,
301    sess: &Session,
302    function_attributes: &Vec<TargetFeature>,
303) -> Option<&'ll Attribute> {
304    if sess.target.arch != Arch::S390x {
305        return None;
306    }
307    if !sess.opts.unstable_opts.packed_stack {
308        return None;
309    }
310
311    // The backchain and softfloat flags can be set via -Ctarget-features=...
312    // or via #[target_features(enable = ...)] so we have to check both possibilities
313    let have_backchain = sess.unstable_target_features.contains(&sym::backchain)
314        || function_attributes.iter().any(|feature| feature.name == sym::backchain);
315    let have_softfloat = sess.unstable_target_features.contains(&sym::soft_float)
316        || function_attributes.iter().any(|feature| feature.name == sym::soft_float);
317
318    // If both, backchain and packedstack, are enabled LLVM cannot generate valid function entry points
319    // with the default ABI. However if the softfloat flag is set LLVM will switch to the softfloat
320    // ABI, where this works.
321    if have_backchain && !have_softfloat {
322        sess.dcx().emit_err(PackedStackBackchainNeedsSoftfloat);
323        return None;
324    }
325
326    Some(llvm::CreateAttrString(cx.llcx, "packed-stack"))
327}
328
329pub(crate) fn target_cpu_attr<'ll>(cx: &SimpleCx<'ll>, sess: &Session) -> &'ll Attribute {
330    let target_cpu = llvm_util::target_cpu(sess);
331    llvm::CreateAttrStringValue(cx.llcx, "target-cpu", target_cpu)
332}
333
334pub(crate) fn tune_cpu_attr<'ll>(cx: &SimpleCx<'ll>, sess: &Session) -> Option<&'ll Attribute> {
335    llvm_util::tune_cpu(sess)
336        .map(|tune_cpu| llvm::CreateAttrStringValue(cx.llcx, "tune-cpu", tune_cpu))
337}
338
339/// Get the `target-features` LLVM attribute.
340pub(crate) fn target_features_attr<'ll, 'tcx>(
341    cx: &SimpleCx<'ll>,
342    tcx: TyCtxt<'tcx>,
343    function_features: Vec<String>,
344) -> Option<&'ll Attribute> {
345    let global_features = tcx.global_backend_features(()).iter().map(String::as_str);
346    let function_features = function_features.iter().map(String::as_str);
347    let target_features =
348        global_features.chain(function_features).intersperse(",").collect::<String>();
349    (!target_features.is_empty())
350        .then(|| llvm::CreateAttrStringValue(cx.llcx, "target-features", &target_features))
351}
352
353/// Get the `NonLazyBind` LLVM attribute,
354/// if the codegen options allow skipping the PLT.
355pub(crate) fn non_lazy_bind_attr<'ll>(
356    cx: &SimpleCx<'ll>,
357    sess: &Session,
358) -> Option<&'ll Attribute> {
359    // Don't generate calls through PLT if it's not necessary
360    if !sess.needs_plt() { Some(AttributeKind::NonLazyBind.create_attr(cx.llcx)) } else { None }
361}
362
363/// Get the default optimizations attrs for a function.
364#[inline]
365pub(crate) fn default_optimisation_attrs<'ll>(
366    cx: &SimpleCx<'ll>,
367    sess: &Session,
368) -> SmallVec<[&'ll Attribute; 2]> {
369    let mut attrs = SmallVec::new();
370    match sess.opts.optimize {
371        OptLevel::Size => {
372            attrs.push(llvm::AttributeKind::OptimizeForSize.create_attr(cx.llcx));
373        }
374        OptLevel::SizeMin => {
375            attrs.push(llvm::AttributeKind::MinSize.create_attr(cx.llcx));
376            attrs.push(llvm::AttributeKind::OptimizeForSize.create_attr(cx.llcx));
377        }
378        _ => {}
379    }
380    attrs
381}
382
383fn create_alloc_family_attr(llcx: &llvm::Context) -> &llvm::Attribute {
384    llvm::CreateAttrStringValue(llcx, "alloc-family", "__rust_alloc")
385}
386
387/// Helper for `FnAbiLlvmExt::apply_attrs_llfn`:
388/// Composite function which sets LLVM attributes for function depending on its AST (`#[attribute]`)
389/// attributes.
390pub(crate) fn llfn_attrs_from_instance<'ll, 'tcx>(
391    cx: &SimpleCx<'ll>,
392    tcx: TyCtxt<'tcx>,
393    llfn: &'ll Value,
394    codegen_fn_attrs: &CodegenFnAttrs,
395    instance: Option<ty::Instance<'tcx>>,
396) {
397    let sess = tcx.sess;
398    let mut to_add = SmallVec::<[_; 16]>::new();
399
400    match codegen_fn_attrs.optimize {
401        OptimizeAttr::Default => {
402            to_add.extend(default_optimisation_attrs(cx, sess));
403        }
404        OptimizeAttr::DoNotOptimize => {
405            to_add.push(llvm::AttributeKind::OptimizeNone.create_attr(cx.llcx));
406        }
407        OptimizeAttr::Size => {
408            to_add.push(llvm::AttributeKind::MinSize.create_attr(cx.llcx));
409            to_add.push(llvm::AttributeKind::OptimizeForSize.create_attr(cx.llcx));
410        }
411        OptimizeAttr::Speed => {}
412    }
413
414    if let Some(instance) = instance {
415        // `optnone` requires `noinline`
416        let inline = match (codegen_fn_attrs.inline, &codegen_fn_attrs.optimize) {
417            (_, OptimizeAttr::DoNotOptimize) => InlineAttr::Never,
418            (InlineAttr::None, _) if instance.def.requires_inline(tcx) => InlineAttr::Hint,
419            (inline, _) => inline,
420        };
421
422        to_add.extend(inline_attr(cx, sess, inline));
423    }
424
425    if sess.must_emit_unwind_tables() {
426        to_add.push(uwtable_attr(cx.llcx, sess.opts.unstable_opts.use_sync_unwind));
427    }
428
429    if sess.opts.unstable_opts.profile_sample_use.is_some() {
430        to_add.push(llvm::CreateAttrString(cx.llcx, "use-sample-profile"));
431    }
432
433    // FIXME: none of these functions interact with source level attributes.
434    to_add.extend(frame_pointer_type_attr(cx, sess));
435    to_add.extend(function_return_attr(cx, sess));
436    to_add.extend(instrument_function_attr(cx, sess));
437    to_add.extend(nojumptables_attr(cx, sess));
438    to_add.extend(probestack_attr(cx, tcx));
439    to_add.extend(stackprotector_attr(cx, sess));
440
441    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NO_BUILTINS) {
442        to_add.push(llvm::CreateAttrString(cx.llcx, "no-builtins"));
443    }
444
445    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::OFFLOAD_KERNEL) {
446        to_add.push(llvm::CreateAttrString(cx.llcx, "offload-kernel"))
447    }
448
449    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
450        to_add.push(AttributeKind::Cold.create_attr(cx.llcx));
451    }
452    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::FFI_PURE) {
453        to_add.push(MemoryEffects::ReadOnly.create_attr(cx.llcx));
454    }
455    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::FFI_CONST) {
456        to_add.push(MemoryEffects::None.create_attr(cx.llcx));
457    }
458    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
459        // do nothing; a naked function is converted into an extern function
460        // and a global assembly block. LLVM's support for naked functions is
461        // not used.
462    } else {
463        // Do not set sanitizer attributes for naked functions.
464        to_add.extend(sanitize_attrs(cx, tcx, codegen_fn_attrs.sanitizers));
465
466        // For non-naked functions, set branch protection attributes on aarch64.
467        if let Some(BranchProtection { bti, pac_ret, gcs }) =
468            sess.opts.unstable_opts.branch_protection
469        {
470            if !(sess.target.arch == Arch::AArch64) {
    ::core::panicking::panic("assertion failed: sess.target.arch == Arch::AArch64")
};assert!(sess.target.arch == Arch::AArch64);
471            if bti {
472                to_add.push(llvm::CreateAttrString(cx.llcx, "branch-target-enforcement"));
473            }
474            if gcs {
475                to_add.push(llvm::CreateAttrString(cx.llcx, "guarded-control-stack"));
476            }
477            if let Some(PacRet { leaf, pc, key }) = pac_ret {
478                if pc {
479                    to_add.push(llvm::CreateAttrString(cx.llcx, "branch-protection-pauth-lr"));
480                }
481                to_add.push(llvm::CreateAttrStringValue(
482                    cx.llcx,
483                    "sign-return-address",
484                    if leaf { "all" } else { "non-leaf" },
485                ));
486                to_add.push(llvm::CreateAttrStringValue(
487                    cx.llcx,
488                    "sign-return-address-key",
489                    if key == PAuthKey::A { "a_key" } else { "b_key" },
490                ));
491            }
492        }
493    }
494    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::ALLOCATOR)
495        || codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::ALLOCATOR_ZEROED)
496    {
497        to_add.push(create_alloc_family_attr(cx.llcx));
498        if let Some(instance) = instance
499            && let Some(name) =
500                {
    {
        'done:
            {
            for i in
                ::rustc_hir::attrs::HasAttrs::get_attrs(instance.def_id(),
                    &tcx) {
                #[allow(unused_imports)]
                use rustc_hir::attrs::AttributeKind::*;
                let i: &rustc_hir::Attribute = i;
                match i {
                    rustc_hir::Attribute::Parsed(RustcAllocatorZeroedVariant {
                        name }) => {
                        break 'done Some(name);
                    }
                    rustc_hir::Attribute::Unparsed(..) =>
                        {}
                        #[deny(unreachable_patterns)]
                        _ => {}
                }
            }
            None
        }
    }
}find_attr!(tcx, instance.def_id(), RustcAllocatorZeroedVariant {name} => name)
501        {
502            to_add.push(llvm::CreateAttrStringValue(
503                cx.llcx,
504                "alloc-variant-zeroed",
505                &mangle_internal_symbol(tcx, name.as_str()),
506            ));
507        }
508        // apply to argument place instead of function
509        let alloc_align = AttributeKind::AllocAlign.create_attr(cx.llcx);
510        attributes::apply_to_llfn(llfn, AttributePlace::Argument(1), &[alloc_align]);
511        to_add.push(llvm::CreateAllocSizeAttr(cx.llcx, 0));
512        let mut flags = AllocKindFlags::Alloc | AllocKindFlags::Aligned;
513        if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::ALLOCATOR) {
514            flags |= AllocKindFlags::Uninitialized;
515        } else {
516            flags |= AllocKindFlags::Zeroed;
517        }
518        to_add.push(llvm::CreateAllocKindAttr(cx.llcx, flags));
519        // apply to return place instead of function (unlike all other attributes applied in this
520        // function)
521        let no_alias = AttributeKind::NoAlias.create_attr(cx.llcx);
522        attributes::apply_to_llfn(llfn, AttributePlace::ReturnValue, &[no_alias]);
523    }
524    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::REALLOCATOR) {
525        to_add.push(create_alloc_family_attr(cx.llcx));
526        to_add.push(llvm::CreateAllocKindAttr(
527            cx.llcx,
528            AllocKindFlags::Realloc | AllocKindFlags::Aligned,
529        ));
530        // applies to argument place instead of function place
531        let allocated_pointer = AttributeKind::AllocatedPointer.create_attr(cx.llcx);
532        attributes::apply_to_llfn(llfn, AttributePlace::Argument(0), &[allocated_pointer]);
533        // apply to argument place instead of function
534        let alloc_align = AttributeKind::AllocAlign.create_attr(cx.llcx);
535        attributes::apply_to_llfn(llfn, AttributePlace::Argument(2), &[alloc_align]);
536        to_add.push(llvm::CreateAllocSizeAttr(cx.llcx, 3));
537        let no_alias = AttributeKind::NoAlias.create_attr(cx.llcx);
538        attributes::apply_to_llfn(llfn, AttributePlace::ReturnValue, &[no_alias]);
539    }
540    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::DEALLOCATOR) {
541        to_add.push(create_alloc_family_attr(cx.llcx));
542        to_add.push(llvm::CreateAllocKindAttr(cx.llcx, AllocKindFlags::Free));
543        // applies to argument place instead of function place
544        let allocated_pointer = AttributeKind::AllocatedPointer.create_attr(cx.llcx);
545        // "Does not capture provenance" means "if the function call stashes the pointer somewhere,
546        // accessing that pointer after the function returns is UB". That is definitely the case here since
547        // freeing will destroy the provenance.
548        let captures_addr = AttributeKind::CapturesAddress.create_attr(cx.llcx);
549        let attrs = &[allocated_pointer, captures_addr];
550        attributes::apply_to_llfn(llfn, AttributePlace::Argument(0), attrs);
551    }
552    if let Some(align) = codegen_fn_attrs.alignment {
553        llvm::set_alignment(llfn, align);
554    }
555    if let Some(packed_stack) = packed_stack_attr(cx, sess, &codegen_fn_attrs.target_features) {
556        to_add.push(packed_stack);
557    }
558    to_add.extend(patchable_function_entry_attrs(
559        cx,
560        sess,
561        codegen_fn_attrs.patchable_function_entry,
562    ));
563
564    // Always annotate functions with the target-cpu they are compiled for.
565    // Without this, ThinLTO won't inline Rust functions into Clang generated
566    // functions (because Clang annotates functions this way too).
567    to_add.push(target_cpu_attr(cx, sess));
568    // tune-cpu is only conveyed through the attribute for our purpose.
569    // The target doesn't care; the subtarget reads our attribute.
570    to_add.extend(tune_cpu_attr(cx, sess));
571
572    let function_features =
573        codegen_fn_attrs.target_features.iter().map(|f| f.name.as_str()).collect::<Vec<&str>>();
574
575    let function_features = function_features
576        .iter()
577        // Convert to LLVMFeatures and filter out unavailable ones
578        .flat_map(|feat| llvm_util::to_llvm_features(sess, feat))
579        // Convert LLVMFeatures & dependencies to +<feats>s
580        .flat_map(|feat| feat.into_iter().map(|f| ::alloc::__export::must_use({ ::alloc::fmt::format(format_args!("+{0}", f)) })format!("+{f}")))
581        .chain(codegen_fn_attrs.instruction_set.iter().map(|x| match x {
582            InstructionSetAttr::ArmA32 => "-thumb-mode".to_string(),
583            InstructionSetAttr::ArmT32 => "+thumb-mode".to_string(),
584        }))
585        .collect::<Vec<String>>();
586
587    if sess.target.is_like_wasm {
588        // If this function is an import from the environment but the wasm
589        // import has a specific module/name, apply them here.
590        if let Some(instance) = instance
591            && let Some(module) = wasm_import_module(tcx, instance.def_id())
592        {
593            to_add.push(llvm::CreateAttrStringValue(cx.llcx, "wasm-import-module", module));
594
595            let name =
596                codegen_fn_attrs.symbol_name.unwrap_or_else(|| tcx.item_name(instance.def_id()));
597            let name = name.as_str();
598            to_add.push(llvm::CreateAttrStringValue(cx.llcx, "wasm-import-name", name));
599        }
600    }
601
602    to_add.extend(target_features_attr(cx, tcx, function_features));
603
604    attributes::apply_to_llfn(llfn, Function, &to_add);
605}
606
607fn wasm_import_module(tcx: TyCtxt<'_>, id: DefId) -> Option<&String> {
608    tcx.wasm_import_module_map(id.krate).get(&id)
609}
rustc_codegen_llvm/attributes.rs

rustc_codegen_llvm/
attributes.rs
