src/librustc_trans/debuginfo/gdb.rs

   1 // Copyright 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
  11 // .debug_gdb_scripts binary section.
  12
  13 use llvm;
  14
  15 use common::{C_bytes, CrateContext, C_i32};
  16 use declare;
  17 use type_::Type;
  18 use session::config::NoDebugInfo;
  19
  20 use std::ffi::CString;
  21 use std::ptr;
  22 use syntax::attr;
  23
  24
  25 /// Inserts a side-effect free instruction sequence that makes sure that the
  26 /// .debug_gdb_scripts global is referenced, so it isn't removed by the linker.
  27 pub fn insert_reference_to_gdb_debug_scripts_section_global(ccx: &CrateContext) {
  28     if needs_gdb_debug_scripts_section(ccx) {
  29         let empty = CString::new("").unwrap();
  30         let gdb_debug_scripts_section_global =
  31             get_or_insert_gdb_debug_scripts_section_global(ccx);
  32         unsafe {
  33             // Load just the first byte as that's all that's necessary to force
  34             // LLVM to keep around the reference to the global.
  35             let indices = [C_i32(ccx, 0), C_i32(ccx, 0)];
  36             let element =
  37                 llvm::LLVMBuildInBoundsGEP(ccx.raw_builder(),
  38                                            gdb_debug_scripts_section_global,
  39                                            indices.as_ptr(),
  40                                            indices.len() as ::libc::c_uint,
  41                                            empty.as_ptr());
  42             let volative_load_instruction =
  43                 llvm::LLVMBuildLoad(ccx.raw_builder(),
  44                                     element,
  45                                     empty.as_ptr());
  46             llvm::LLVMSetVolatile(volative_load_instruction, llvm::True);
  47             llvm::LLVMSetAlignment(volative_load_instruction, 1);
  48         }
  49     }
  50 }
  51
  52 /// Allocates the global variable responsible for the .debug_gdb_scripts binary
  53 /// section.
  54 pub fn get_or_insert_gdb_debug_scripts_section_global(ccx: &CrateContext)
  55                                                   -> llvm::ValueRef {
  56     let c_section_var_name = "__rustc_debug_gdb_scripts_section__\0";
  57     let section_var_name = &c_section_var_name[..c_section_var_name.len()-1];
  58
  59     let section_var = unsafe {
  60         llvm::LLVMGetNamedGlobal(ccx.llmod(),
  61                                  c_section_var_name.as_ptr() as *const _)
  62     };
  63
  64     if section_var == ptr::null_mut() {
  65         let section_name = b".debug_gdb_scripts\0";
  66         let section_contents = b"\x01gdb_load_rust_pretty_printers.py\0";
  67
  68         unsafe {
  69             let llvm_type = Type::array(&Type::i8(ccx),
  70                                         section_contents.len() as u64);
  71
  72             let section_var = declare::define_global(ccx, section_var_name,
  73                                                      llvm_type).unwrap_or_else(||{
  74                 bug!("symbol `{}` is already defined", section_var_name)
  75             });
  76             llvm::LLVMSetSection(section_var, section_name.as_ptr() as *const _);
  77             llvm::LLVMSetInitializer(section_var, C_bytes(ccx, section_contents));
  78             llvm::LLVMSetGlobalConstant(section_var, llvm::True);
  79             llvm::LLVMSetUnnamedAddr(section_var, llvm::True);
  80             llvm::SetLinkage(section_var, llvm::Linkage::LinkOnceODRLinkage);
  81             // This should make sure that the whole section is not larger than
  82             // the string it contains. Otherwise we get a warning from GDB.
  83             llvm::LLVMSetAlignment(section_var, 1);
  84             section_var
  85         }
  86     } else {
  87         section_var
  88     }
  89 }
  90
  91 pub fn needs_gdb_debug_scripts_section(ccx: &CrateContext) -> bool {
  92     let omit_gdb_pretty_printer_section =
  93         attr::contains_name(&ccx.tcx().map.krate_attrs(),
  94                             "omit_gdb_pretty_printer_section");
  95
  96     !omit_gdb_pretty_printer_section &&
  97     !ccx.sess().target.target.options.is_like_osx &&
  98     !ccx.sess().target.target.options.is_like_windows &&
  99     ccx.sess().opts.debuginfo != NoDebugInfo
 100 }