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 rustc::session::config::DebugInfo;
  19 use type_::Type;
  20 use value::Value;
  21 use traits::BuilderMethods;
  22
  23 use syntax::attr;
  24
  25
  26 /// Inserts a side-effect free instruction sequence that makes sure that the
  27 /// .debug_gdb_scripts global is referenced, so it isn't removed by the linker.
  28 pub fn insert_reference_to_gdb_debug_scripts_section_global(bx: &Builder) {
  29     if needs_gdb_debug_scripts_section(bx.cx) {
  30         let gdb_debug_scripts_section = get_or_insert_gdb_debug_scripts_section_global(bx.cx);
  31         // Load just the first byte as that's all that's necessary to force
  32         // LLVM to keep around the reference to the global.
  33         let indices = [C_i32(bx.cx, 0), C_i32(bx.cx, 0)];
  34         let element = bx.inbounds_gep(gdb_debug_scripts_section, &indices);
  35         let volative_load_instruction = bx.volatile_load(element);
  36         unsafe {
  37             llvm::LLVMSetAlignment(volative_load_instruction, 1);
  38         }
  39     }
  40 }
  41
  42 /// Allocates the global variable responsible for the .debug_gdb_scripts binary
  43 /// section.
  44 pub fn get_or_insert_gdb_debug_scripts_section_global(cx: &CodegenCx<'ll, '_>)
  45                                                   -> &'ll Value {
  46     let c_section_var_name = "__rustc_debug_gdb_scripts_section__\0";
  47     let section_var_name = &c_section_var_name[..c_section_var_name.len()-1];
  48
  49     let section_var = unsafe {
  50         llvm::LLVMGetNamedGlobal(cx.llmod,
  51                                  c_section_var_name.as_ptr() as *const _)
  52     };
  53
  54     section_var.unwrap_or_else(|| {
  55         let section_name = b".debug_gdb_scripts\0";
  56         let section_contents = b"\x01gdb_load_rust_pretty_printers.py\0";
  57
  58         unsafe {
  59             let llvm_type = Type::array::<Value>(Type::i8(cx),
  60                                         section_contents.len() as u64);
  61
  62             let section_var = declare::define_global(cx, section_var_name,
  63                                                      llvm_type).unwrap_or_else(||{
  64                 bug!("symbol `{}` is already defined", section_var_name)
  65             });
  66             llvm::LLVMSetSection(section_var, section_name.as_ptr() as *const _);
  67             llvm::LLVMSetInitializer(section_var, C_bytes(cx, section_contents));
  68             llvm::LLVMSetGlobalConstant(section_var, llvm::True);
  69             llvm::LLVMSetUnnamedAddr(section_var, llvm::True);
  70             llvm::LLVMRustSetLinkage(section_var, llvm::Linkage::LinkOnceODRLinkage);
  71             // This should make sure that the whole section is not larger than
  72             // the string it contains. Otherwise we get a warning from GDB.
  73             llvm::LLVMSetAlignment(section_var, 1);
  74             section_var
  75         }
  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 != DebugInfo::None &&
  86     cx.sess().target.target.options.emit_debug_gdb_scripts
  87 }