src/librustc_trans/attributes.rs

   1 // Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10 //! Set and unset common attributes on LLVM values.
  11
  12 use std::ffi::{CStr, CString};
  13
  14 use rustc::session::config::Sanitizer;
  15
  16 use llvm::{self, Attribute, ValueRef};
  17 use llvm::AttributePlace::Function;
  18 pub use syntax::attr::{self, InlineAttr};
  19 use syntax::ast;
  20 use context::CrateContext;
  21
  22 /// Mark LLVM function to use provided inline heuristic.
  23 #[inline]
  24 pub fn inline(val: ValueRef, inline: InlineAttr) {
  25     use self::InlineAttr::*;
  26     match inline {
  27         Hint   => Attribute::InlineHint.apply_llfn(Function, val),
  28         Always => Attribute::AlwaysInline.apply_llfn(Function, val),
  29         Never  => Attribute::NoInline.apply_llfn(Function, val),
  30         None   => {
  31             Attribute::InlineHint.unapply_llfn(Function, val);
  32             Attribute::AlwaysInline.unapply_llfn(Function, val);
  33             Attribute::NoInline.unapply_llfn(Function, val);
  34         },
  35     };
  36 }
  37
  38 /// Tell LLVM to emit or not emit the information necessary to unwind the stack for the function.
  39 #[inline]
  40 pub fn emit_uwtable(val: ValueRef, emit: bool) {
  41     Attribute::UWTable.toggle_llfn(Function, val, emit);
  42 }
  43
  44 /// Tell LLVM whether the function can or cannot unwind.
  45 #[inline]
  46 pub fn unwind(val: ValueRef, can_unwind: bool) {
  47     Attribute::NoUnwind.toggle_llfn(Function, val, !can_unwind);
  48 }
  49
  50 /// Tell LLVM whether it should optimize function for size.
  51 #[inline]
  52 #[allow(dead_code)] // possibly useful function
  53 pub fn set_optimize_for_size(val: ValueRef, optimize: bool) {
  54     Attribute::OptimizeForSize.toggle_llfn(Function, val, optimize);
  55 }
  56
  57 /// Tell LLVM if this function should be 'naked', i.e. skip the epilogue and prologue.
  58 #[inline]
  59 pub fn naked(val: ValueRef, is_naked: bool) {
  60     Attribute::Naked.toggle_llfn(Function, val, is_naked);
  61 }
  62
  63 pub fn set_frame_pointer_elimination(ccx: &CrateContext, llfn: ValueRef) {
  64     // FIXME: #11906: Omitting frame pointers breaks retrieving the value of a
  65     // parameter.
  66     if ccx.sess().must_not_eliminate_frame_pointers() {
  67         llvm::AddFunctionAttrStringValue(
  68             llfn, llvm::AttributePlace::Function,
  69             cstr("no-frame-pointer-elim\0"), cstr("true\0"));
  70     }
  71 }
  72
  73 pub fn set_probestack(ccx: &CrateContext, llfn: ValueRef) {
  74     // Only use stack probes if the target specification indicates that we
  75     // should be using stack probes
  76     if !ccx.sess().target.target.options.stack_probes {
  77         return
  78     }
  79
  80     // Currently stack probes seem somewhat incompatible with the address
  81     // sanitizer. With asan we're already protected from stack overflow anyway
  82     // so we don't really need stack probes regardless.
  83     match ccx.sess().opts.debugging_opts.sanitizer {
  84         Some(Sanitizer::Address) => return,
  85         _ => {}
  86     }
  87
  88     // Flag our internal `__rust_probestack` function as the stack probe symbol.
  89     // This is defined in the `compiler-builtins` crate for each architecture.
  90     llvm::AddFunctionAttrStringValue(
  91         llfn, llvm::AttributePlace::Function,
  92         cstr("probe-stack\0"), cstr("__rust_probestack\0"));
  93 }
  94
  95 /// Composite function which sets LLVM attributes for function depending on its AST (#[attribute])
  96 /// attributes.
  97 pub fn from_fn_attrs(ccx: &CrateContext, attrs: &[ast::Attribute], llfn: ValueRef) {
  98     use syntax::attr::*;
  99     inline(llfn, find_inline_attr(Some(ccx.sess().diagnostic()), attrs));
 100
 101     set_frame_pointer_elimination(ccx, llfn);
 102     set_probestack(ccx, llfn);
 103     let mut target_features = vec![];
 104     for attr in attrs {
 105         if attr.check_name("target_feature") {
 106             if let Some(val) = attr.value_str() {
 107                 for feat in val.as_str().split(",").map(|f| f.trim()) {
 108                     if !feat.is_empty() && !feat.contains('\0') {
 109                         target_features.push(feat.to_string());
 110                     }
 111                 }
 112             }
 113         } else if attr.check_name("cold") {
 114             Attribute::Cold.apply_llfn(Function, llfn);
 115         } else if attr.check_name("naked") {
 116             naked(llfn, true);
 117         } else if attr.check_name("allocator") {
 118             Attribute::NoAlias.apply_llfn(
 119                 llvm::AttributePlace::ReturnValue, llfn);
 120         } else if attr.check_name("unwind") {
 121             unwind(llfn, true);
 122         } else if attr.check_name("rustc_allocator_nounwind") {
 123             unwind(llfn, false);
 124         }
 125     }
 126     if !target_features.is_empty() {
 127         let val = CString::new(target_features.join(",")).unwrap();
 128         llvm::AddFunctionAttrStringValue(
 129             llfn, llvm::AttributePlace::Function,
 130             cstr("target-features\0"), &val);
 131     }
 132 }
 133
 134 fn cstr(s: &'static str) -> &CStr {
 135     CStr::from_bytes_with_nul(s.as_bytes()).expect("null-terminated string")
 136 }