src/librustc_codegen_llvm/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, CodegenCx, C_i32};
  16 use builder::Builder;
  17 use declare;
  18 use type_::Type;
  19 use rustc::session::config::NoDebugInfo;
  20
  21 use syntax::attr;
  22
  23
  24 /// Inserts a side-effect free instruction sequence that makes sure that the
  25 /// .debug_gdb_scripts global is referenced, so it isn't removed by the linker.
  26 pub fn insert_reference_to_gdb_debug_scripts_section_global(bx: &Builder) {
  27     if needs_gdb_debug_scripts_section(bx.cx) {
  28         let gdb_debug_scripts_section = get_or_insert_gdb_debug_scripts_section_global(bx.cx);
  29         // Load just the first byte as that's all that's necessary to force
  30         // LLVM to keep around the reference to the global.
  31         let indices = [C_i32(bx.cx, 0), C_i32(bx.cx, 0)];
  32         let element = bx.inbounds_gep(gdb_debug_scripts_section, &indices);
  33         let volative_load_instruction = bx.volatile_load(element);
  34         unsafe {
  35             llvm::LLVMSetAlignment(volative_load_instruction, 1);
  36         }
  37     }
  38 }
  39
  40 /// Allocates the global variable responsible for the .debug_gdb_scripts binary
  41 /// section.
  42 pub fn get_or_insert_gdb_debug_scripts_section_global(cx: &CodegenCx)
  43                                                   -> llvm::ValueRef {
  44     let c_section_var_name = "__rustc_debug_gdb_scripts_section__\0";
  45     let section_var_name = &c_section_var_name[..c_section_var_name.len()-1];
  46
  47     let section_var = unsafe {
  48         llvm::LLVMGetNamedGlobal(cx.llmod,
  49                                  c_section_var_name.as_ptr() as *const _)
  50     };
  51
  52     if section_var.is_null() {
  53         let section_name = b".debug_gdb_scripts\0";
  54         let section_contents = b"\x01gdb_load_rust_pretty_printers.py\0";
  55
  56         unsafe {
  57             let llvm_type = Type::array(&Type::i8(cx),
  58                                         section_contents.len() as u64);
  59
  60             let section_var = declare::define_global(cx, section_var_name,
  61                                                      llvm_type).unwrap_or_else(||{
  62                 bug!("symbol `{}` is already defined", section_var_name)
  63             });
  64             llvm::LLVMSetSection(section_var, section_name.as_ptr() as *const _);
  65             llvm::LLVMSetInitializer(section_var, C_bytes(cx, section_contents));
  66             llvm::LLVMSetGlobalConstant(section_var, llvm::True);
  67             llvm::LLVMSetUnnamedAddr(section_var, llvm::True);
  68             llvm::LLVMRustSetLinkage(section_var, llvm::Linkage::LinkOnceODRLinkage);
  69             // This should make sure that the whole section is not larger than
  70             // the string it contains. Otherwise we get a warning from GDB.
  71             llvm::LLVMSetAlignment(section_var, 1);
  72             section_var
  73         }
  74     } else {
  75         section_var
  76     }
  77 }
  78
  79 pub fn needs_gdb_debug_scripts_section(cx: &CodegenCx) -> bool {
  80     let omit_gdb_pretty_printer_section =
  81         attr::contains_name(&cx.tcx.hir.krate_attrs(),
  82                             "omit_gdb_pretty_printer_section");
  83
  84     !omit_gdb_pretty_printer_section &&
  85     cx.sess().opts.debuginfo != NoDebugInfo &&
  86     cx.sess().target.target.options.emit_debug_gdb_scripts
  87 }