src/librustc_codegen_llvm/debuginfo/gdb.rs

   1 // .debug_gdb_scripts binary section.
   2
   3 use crate::llvm;
   4
   5 use crate::common::CodegenCx;
   6 use crate::builder::Builder;
   7 use crate::value::Value;
   8 use rustc::session::config::DebugInfo;
   9 use rustc_codegen_ssa::traits::*;
  10
  11 use syntax::attr;
  12
  13
  14 /// Inserts a side-effect free instruction sequence that makes sure that the
  15 /// .debug_gdb_scripts global is referenced, so it isn't removed by the linker.
  16 pub fn insert_reference_to_gdb_debug_scripts_section_global(bx: &mut Builder) {
  17     if needs_gdb_debug_scripts_section(bx) {
  18         let gdb_debug_scripts_section = get_or_insert_gdb_debug_scripts_section_global(bx);
  19         // Load just the first byte as that's all that's necessary to force
  20         // LLVM to keep around the reference to the global.
  21         let indices = [bx.const_i32(0), bx.const_i32(0)];
  22         let element = bx.inbounds_gep(gdb_debug_scripts_section, &indices);
  23         let volative_load_instruction = bx.volatile_load(element);
  24         unsafe {
  25             llvm::LLVMSetAlignment(volative_load_instruction, 1);
  26         }
  27     }
  28 }
  29
  30 /// Allocates the global variable responsible for the .debug_gdb_scripts binary
  31 /// section.
  32 pub fn get_or_insert_gdb_debug_scripts_section_global(cx: &CodegenCx<'ll, '_>)
  33                                                   -> &'ll Value {
  34     let c_section_var_name = "__rustc_debug_gdb_scripts_section__\0";
  35     let section_var_name = &c_section_var_name[..c_section_var_name.len()-1];
  36
  37     let section_var = unsafe {
  38         llvm::LLVMGetNamedGlobal(cx.llmod,
  39                                  c_section_var_name.as_ptr() as *const _)
  40     };
  41
  42     section_var.unwrap_or_else(|| {
  43         let section_name = b".debug_gdb_scripts\0";
  44         let section_contents = b"\x01gdb_load_rust_pretty_printers.py\0";
  45
  46         unsafe {
  47             let llvm_type = cx.type_array(cx.type_i8(),
  48                                         section_contents.len() as u64);
  49
  50             let section_var = cx.define_global(section_var_name,
  51                                                      llvm_type).unwrap_or_else(||{
  52                 bug!("symbol `{}` is already defined", section_var_name)
  53             });
  54             llvm::LLVMSetSection(section_var, section_name.as_ptr() as *const _);
  55             llvm::LLVMSetInitializer(section_var, cx.const_bytes(section_contents));
  56             llvm::LLVMSetGlobalConstant(section_var, llvm::True);
  57             llvm::LLVMSetUnnamedAddr(section_var, llvm::True);
  58             llvm::LLVMRustSetLinkage(section_var, llvm::Linkage::LinkOnceODRLinkage);
  59             // This should make sure that the whole section is not larger than
  60             // the string it contains. Otherwise we get a warning from GDB.
  61             llvm::LLVMSetAlignment(section_var, 1);
  62             section_var
  63         }
  64     })
  65 }
  66
  67 pub fn needs_gdb_debug_scripts_section(cx: &CodegenCx) -> bool {
  68     let omit_gdb_pretty_printer_section =
  69         attr::contains_name(&cx.tcx.hir().krate_attrs(),
  70                             "omit_gdb_pretty_printer_section");
  71
  72     !omit_gdb_pretty_printer_section &&
  73     cx.sess().opts.debuginfo != DebugInfo::None &&
  74     cx.sess().target.target.options.emit_debug_gdb_scripts
  75 }