diff options
Diffstat (limited to 'compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs')
-rw-r--r-- | compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs | 120 |
1 files changed, 120 insertions, 0 deletions
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs b/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs new file mode 100644 index 000000000..80fd9726f --- /dev/null +++ b/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs @@ -0,0 +1,120 @@ +// .debug_gdb_scripts binary section. + +use crate::llvm; + +use crate::builder::Builder; +use crate::common::CodegenCx; +use crate::value::Value; +use rustc_codegen_ssa::base::collect_debugger_visualizers_transitive; +use rustc_codegen_ssa::traits::*; +use rustc_hir::def_id::LOCAL_CRATE; +use rustc_middle::bug; +use rustc_session::config::{CrateType, DebugInfo}; + +use rustc_span::symbol::sym; +use rustc_span::DebuggerVisualizerType; + +/// Inserts a side-effect free instruction sequence that makes sure that the +/// .debug_gdb_scripts global is referenced, so it isn't removed by the linker. +pub fn insert_reference_to_gdb_debug_scripts_section_global(bx: &mut Builder<'_, '_, '_>) { + if needs_gdb_debug_scripts_section(bx) { + let gdb_debug_scripts_section = + bx.const_bitcast(get_or_insert_gdb_debug_scripts_section_global(bx), bx.type_i8p()); + // Load just the first byte as that's all that's necessary to force + // LLVM to keep around the reference to the global. + let volative_load_instruction = bx.volatile_load(bx.type_i8(), gdb_debug_scripts_section); + unsafe { + llvm::LLVMSetAlignment(volative_load_instruction, 1); + } + } +} + +/// Allocates the global variable responsible for the .debug_gdb_scripts binary +/// section. +pub fn get_or_insert_gdb_debug_scripts_section_global<'ll>(cx: &CodegenCx<'ll, '_>) -> &'ll Value { + let c_section_var_name = "__rustc_debug_gdb_scripts_section__\0"; + let section_var_name = &c_section_var_name[..c_section_var_name.len() - 1]; + + let section_var = + unsafe { llvm::LLVMGetNamedGlobal(cx.llmod, c_section_var_name.as_ptr().cast()) }; + + section_var.unwrap_or_else(|| { + let section_name = b".debug_gdb_scripts\0"; + let mut section_contents = Vec::new(); + + // Add the pretty printers for the standard library first. + section_contents.extend_from_slice(b"\x01gdb_load_rust_pretty_printers.py\0"); + + // Next, add the pretty printers that were specified via the `#[debugger_visualizer]` attribute. + let visualizers = collect_debugger_visualizers_transitive( + cx.tcx, + DebuggerVisualizerType::GdbPrettyPrinter, + ); + let crate_name = cx.tcx.crate_name(LOCAL_CRATE); + for (index, visualizer) in visualizers.iter().enumerate() { + // The initial byte `4` instructs GDB that the following pretty printer + // is defined inline as opposed to in a standalone file. + section_contents.extend_from_slice(b"\x04"); + let vis_name = format!("pretty-printer-{}-{}\n", crate_name, index); + section_contents.extend_from_slice(vis_name.as_bytes()); + section_contents.extend_from_slice(&visualizer.src); + + // The final byte `0` tells GDB that the pretty printer has been + // fully defined and can continue searching for additional + // pretty printers. + section_contents.extend_from_slice(b"\0"); + } + + unsafe { + let section_contents = section_contents.as_slice(); + let llvm_type = cx.type_array(cx.type_i8(), section_contents.len() as u64); + + let section_var = cx + .define_global(section_var_name, llvm_type) + .unwrap_or_else(|| bug!("symbol `{}` is already defined", section_var_name)); + llvm::LLVMSetSection(section_var, section_name.as_ptr().cast()); + llvm::LLVMSetInitializer(section_var, cx.const_bytes(section_contents)); + llvm::LLVMSetGlobalConstant(section_var, llvm::True); + llvm::LLVMSetUnnamedAddress(section_var, llvm::UnnamedAddr::Global); + llvm::LLVMRustSetLinkage(section_var, llvm::Linkage::LinkOnceODRLinkage); + // This should make sure that the whole section is not larger than + // the string it contains. Otherwise we get a warning from GDB. + llvm::LLVMSetAlignment(section_var, 1); + section_var + } + }) +} + +pub fn needs_gdb_debug_scripts_section(cx: &CodegenCx<'_, '_>) -> bool { + let omit_gdb_pretty_printer_section = + cx.tcx.sess.contains_name(cx.tcx.hir().krate_attrs(), sym::omit_gdb_pretty_printer_section); + + // To ensure the section `__rustc_debug_gdb_scripts_section__` will not create + // ODR violations at link time, this section will not be emitted for rlibs since + // each rlib could produce a different set of visualizers that would be embedded + // in the `.debug_gdb_scripts` section. For that reason, we make sure that the + // section is only emitted for leaf crates. + let embed_visualizers = cx.sess().crate_types().iter().any(|&crate_type| match crate_type { + CrateType::Executable | CrateType::Dylib | CrateType::Cdylib | CrateType::Staticlib => { + // These are crate types for which we will embed pretty printers since they + // are treated as leaf crates. + true + } + CrateType::ProcMacro => { + // We could embed pretty printers for proc macro crates too but it does not + // seem like a good default, since this is a rare use case and we don't + // want to slow down the common case. + false + } + CrateType::Rlib => { + // As per the above description, embedding pretty printers for rlibs could + // lead to ODR violations so we skip this crate type as well. + false + } + }); + + !omit_gdb_pretty_printer_section + && cx.sess().opts.debuginfo != DebugInfo::None + && cx.sess().target.emit_debug_gdb_scripts + && embed_visualizers +} |