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
+}