src/librustc_codegen_llvm/debuginfo/gdb.rs

   1 // .debug_gdb_scripts binary section.
   2
   3 use crate::llvm;
   4
   5 use crate::builder::Builder;
   6 use crate::common::CodegenCx;
   7 use crate::value::Value;
   8 use rustc_codegen_ssa::traits::*;
   9 use rustc_middle::bug;
  10 use rustc_session::config::DebugInfo;
  11
  12 use rustc_span::symbol::sym;
  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, '_>) -> &'ll Value {
  33     let c_section_var_name = "__rustc_debug_gdb_scripts_section__\0";
  34     let section_var_name = &c_section_var_name[..c_section_var_name.len() - 1];
  35
  36     let section_var =
  37         unsafe { llvm::LLVMGetNamedGlobal(cx.llmod, c_section_var_name.as_ptr().cast()) };
  38
  39     section_var.unwrap_or_else(|| {
  40         let section_name = b".debug_gdb_scripts\0";
  41         let section_contents = b"\x01gdb_load_rust_pretty_printers.py\0";
  42
  43         unsafe {
  44             let llvm_type = cx.type_array(cx.type_i8(), section_contents.len() as u64);
  45
  46             let section_var = cx
  47                 .define_global(section_var_name, llvm_type)
  48                 .unwrap_or_else(|| bug!("symbol `{}` is already defined", section_var_name));
  49             llvm::LLVMSetSection(section_var, section_name.as_ptr().cast());
  50             llvm::LLVMSetInitializer(section_var, cx.const_bytes(section_contents));
  51             llvm::LLVMSetGlobalConstant(section_var, llvm::True);
  52             llvm::LLVMSetUnnamedAddress(section_var, llvm::UnnamedAddr::Global);
  53             llvm::LLVMRustSetLinkage(section_var, llvm::Linkage::LinkOnceODRLinkage);
  54             // This should make sure that the whole section is not larger than
  55             // the string it contains. Otherwise we get a warning from GDB.
  56             llvm::LLVMSetAlignment(section_var, 1);
  57             section_var
  58         }
  59     })
  60 }
  61
  62 pub fn needs_gdb_debug_scripts_section(cx: &CodegenCx<'_, '_>) -> bool {
  63     let omit_gdb_pretty_printer_section = cx
  64         .tcx
  65         .sess
  66         .contains_name(&cx.tcx.hir().krate_attrs(), sym::omit_gdb_pretty_printer_section);
  67
  68     !omit_gdb_pretty_printer_section
  69         && cx.sess().opts.debuginfo != DebugInfo::None
  70         && cx.sess().target.target.options.emit_debug_gdb_scripts
  71 }