From 868bdde25b030e0b71a29a5dbc04a891036e702e Mon Sep 17 00:00:00 2001 From: Sebastian Poeplau Date: Fri, 1 Aug 2025 12:39:50 +0200 Subject: Preserve the .debug_gdb_scripts section Make sure that compiler and linker don't optimize the section's contents away by adding the global holding the data to "llvm.used". The volatile load in the main shim is retained because "llvm.used", which translates to SHF_GNU_RETAIN on ELF targets, requires a reasonably recent linker; emitting the volatile load ensures compatibility with older linkers, at least when libstd is used. Pretty printers in dylib dependencies are now emitted by the main crate instead of the dylib; apart from matching how rlibs are handled, this approach has the advantage that `omit_gdb_pretty_printer_section` keeps working with dylib dependencies. --- compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs | 30 +++++++++++--------- compiler/rustc_codegen_llvm/src/debuginfo/mod.rs | 36 +++++++++++++++--------- 2 files changed, 38 insertions(+), 28 deletions(-) (limited to 'compiler/rustc_codegen_llvm/src/debuginfo') diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs b/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs index 6eb7042da61..b3e978be570 100644 --- a/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs +++ b/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs @@ -1,5 +1,7 @@ // .debug_gdb_scripts binary section. +use std::ffi::CString; + use rustc_codegen_ssa::base::collect_debugger_visualizers_transitive; use rustc_codegen_ssa::traits::*; use rustc_hir::def_id::LOCAL_CRATE; @@ -31,7 +33,12 @@ pub(crate) fn insert_reference_to_gdb_debug_scripts_section_global(bx: &mut Buil pub(crate) fn get_or_insert_gdb_debug_scripts_section_global<'ll>( cx: &CodegenCx<'ll, '_>, ) -> &'ll Value { - let c_section_var_name = c"__rustc_debug_gdb_scripts_section__"; + let c_section_var_name = CString::new(format!( + "__rustc_debug_gdb_scripts_section_{}_{:08x}", + cx.tcx.crate_name(LOCAL_CRATE), + cx.tcx.stable_crate_id(LOCAL_CRATE), + )) + .unwrap(); let section_var_name = c_section_var_name.to_str().unwrap(); let section_var = unsafe { llvm::LLVMGetNamedGlobal(cx.llmod, c_section_var_name.as_ptr()) }; @@ -84,17 +91,10 @@ pub(crate) fn get_or_insert_gdb_debug_scripts_section_global<'ll>( } pub(crate) fn needs_gdb_debug_scripts_section(cx: &CodegenCx<'_, '_>) -> bool { - // 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. + // We collect pretty printers transitively for all crates, so we make sure + // that the section is only emitted for leaf crates. let embed_visualizers = cx.tcx.crate_types().iter().any(|&crate_type| match crate_type { - CrateType::Executable - | CrateType::Dylib - | CrateType::Cdylib - | CrateType::Staticlib - | CrateType::Sdylib => { + CrateType::Executable | CrateType::Cdylib | CrateType::Staticlib | CrateType::Sdylib => { // These are crate types for which we will embed pretty printers since they // are treated as leaf crates. true @@ -105,9 +105,11 @@ pub(crate) fn needs_gdb_debug_scripts_section(cx: &CodegenCx<'_, '_>) -> bool { // 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. + CrateType::Rlib | CrateType::Dylib => { + // Don't embed pretty printers for these crate types; the compiler + // can see the `#[debug_visualizer]` attributes when using the + // library, and emitting `.debug_gdb_scripts` regardless would + // break `#![omit_gdb_pretty_printer_section]`. false } }); diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs b/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs index 6cbf2dbf7d3..c911435967c 100644 --- a/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs +++ b/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs @@ -30,7 +30,7 @@ use tracing::debug; use self::metadata::{UNKNOWN_COLUMN_NUMBER, UNKNOWN_LINE_NUMBER, file_metadata, type_di_node}; use self::namespace::mangled_name_of_instance; -use self::utils::{DIB, create_DIArray, is_node_local_to_unit}; +use self::utils::{DIB, create_DIArray, debug_context, is_node_local_to_unit}; use crate::builder::Builder; use crate::common::{AsCCharPtr, CodegenCx}; use crate::llvm; @@ -131,20 +131,28 @@ impl<'ll, 'tcx> CodegenUnitDebugContext<'ll, 'tcx> { } /// Creates any deferred debug metadata nodes -pub(crate) fn finalize(cx: &CodegenCx<'_, '_>) { - if let Some(dbg_cx) = &cx.dbg_cx { - debug!("finalize"); - - if gdb::needs_gdb_debug_scripts_section(cx) { - // Add a .debug_gdb_scripts section to this compile-unit. This will - // cause GDB to try and load the gdb_load_rust_pretty_printers.py file, - // which activates the Rust pretty printers for binary this section is - // contained in. - gdb::get_or_insert_gdb_debug_scripts_section_global(cx); - } +pub(crate) fn finalize(cx: &mut CodegenCx<'_, '_>) { + if cx.dbg_cx.is_none() { + return; + } + + debug!("finalize"); - dbg_cx.finalize(cx.sess()); + if gdb::needs_gdb_debug_scripts_section(cx) { + // Add a .debug_gdb_scripts section to this compile-unit. This will + // cause GDB to try and load the gdb_load_rust_pretty_printers.py file, + // which activates the Rust pretty printers for binary this section is + // contained in. + let section_var = gdb::get_or_insert_gdb_debug_scripts_section_global(cx); + + // Make sure that the linker doesn't optimize the global away. Adding + // it to `llvm.used` has the advantage that it works even in no_std + // binaries, where we don't have a main shim and thus don't emit a + // volatile load to preserve the global. + cx.add_used_global(section_var); } + + debug_context(cx).finalize(cx.sess()); } impl<'ll> Builder<'_, 'll, '_> { @@ -614,7 +622,7 @@ impl<'ll, 'tcx> DebugInfoCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> { metadata::extend_scope_to_file(self, scope_metadata, file) } - fn debuginfo_finalize(&self) { + fn debuginfo_finalize(&mut self) { finalize(self) } -- cgit 1.4.1-3-g733a5 From b4d923cea0509933b1fb859930cb20784251f9be Mon Sep 17 00:00:00 2001 From: Sebastian Poeplau Date: Fri, 1 Aug 2025 13:22:06 +0200 Subject: Embed GDB pretty printers in rlibs and dylibs Instead of collecting pretty printers transitively when building executables/staticlibs/cdylibs, let the debugger find each crate's pretty printers via its .debug_gdb_scripts section. This covers the case where libraries defining custom pretty printers are loaded dynamically. --- compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs | 43 ++++++---------------- compiler/rustc_codegen_ssa/src/base.rs | 10 ++++- .../compiletest/src/directives/directive_names.rs | 1 + tests/debuginfo/embedded-visualizer.rs | 2 + 4 files changed, 23 insertions(+), 33 deletions(-) (limited to 'compiler/rustc_codegen_llvm/src/debuginfo') diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs b/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs index b3e978be570..fccd32dec95 100644 --- a/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs +++ b/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs @@ -1,13 +1,13 @@ // .debug_gdb_scripts binary section. +use std::collections::BTreeSet; use std::ffi::CString; -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_middle::middle::debugger_visualizer::DebuggerVisualizerType; -use rustc_session::config::{CrateType, DebugInfo}; +use rustc_session::config::DebugInfo; use crate::builder::Builder; use crate::common::CodegenCx; @@ -51,10 +51,14 @@ pub(crate) fn get_or_insert_gdb_debug_scripts_section_global<'ll>( // Next, add the pretty printers that were specified via the `#[debugger_visualizer]` // attribute. - let visualizers = collect_debugger_visualizers_transitive( - cx.tcx, - DebuggerVisualizerType::GdbPrettyPrinter, - ); + let visualizers = cx + .tcx + .debugger_visualizers(LOCAL_CRATE) + .iter() + .filter(|visualizer| { + visualizer.visualizer_type == DebuggerVisualizerType::GdbPrettyPrinter + }) + .collect::>(); 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 @@ -91,30 +95,5 @@ pub(crate) fn get_or_insert_gdb_debug_scripts_section_global<'ll>( } pub(crate) fn needs_gdb_debug_scripts_section(cx: &CodegenCx<'_, '_>) -> bool { - // We collect pretty printers transitively for all crates, so we make sure - // that the section is only emitted for leaf crates. - let embed_visualizers = cx.tcx.crate_types().iter().any(|&crate_type| match crate_type { - CrateType::Executable | CrateType::Cdylib | CrateType::Staticlib | CrateType::Sdylib => { - // 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 | CrateType::Dylib => { - // Don't embed pretty printers for these crate types; the compiler - // can see the `#[debug_visualizer]` attributes when using the - // library, and emitting `.debug_gdb_scripts` regardless would - // break `#![omit_gdb_pretty_printer_section]`. - false - } - }); - - cx.sess().opts.debuginfo != DebugInfo::None - && cx.sess().target.emit_debug_gdb_scripts - && embed_visualizers + cx.sess().opts.debuginfo != DebugInfo::None && cx.sess().target.emit_debug_gdb_scripts } diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs index eb21468650c..b4556ced0b3 100644 --- a/compiler/rustc_codegen_ssa/src/base.rs +++ b/compiler/rustc_codegen_ssa/src/base.rs @@ -609,7 +609,15 @@ pub fn collect_debugger_visualizers_transitive( ) -> BTreeSet { tcx.debugger_visualizers(LOCAL_CRATE) .iter() - .chain(tcx.crates(()).iter().flat_map(|&cnum| tcx.debugger_visualizers(cnum))) + .chain( + tcx.crates(()) + .iter() + .filter(|&cnum| { + let used_crate_source = tcx.used_crate_source(*cnum); + used_crate_source.rlib.is_some() || used_crate_source.rmeta.is_some() + }) + .flat_map(|&cnum| tcx.debugger_visualizers(cnum)), + ) .filter(|visualizer| visualizer.visualizer_type == visualizer_type) .cloned() .collect::>() diff --git a/src/tools/compiletest/src/directives/directive_names.rs b/src/tools/compiletest/src/directives/directive_names.rs index f7955429d83..099058bf051 100644 --- a/src/tools/compiletest/src/directives/directive_names.rs +++ b/src/tools/compiletest/src/directives/directive_names.rs @@ -68,6 +68,7 @@ pub(crate) const KNOWN_DIRECTIVE_NAMES: &[&str] = &[ "ignore-gnu", "ignore-haiku", "ignore-horizon", + "ignore-i586-unknown-linux-gnu", "ignore-i686-pc-windows-gnu", "ignore-i686-pc-windows-msvc", "ignore-illumos", diff --git a/tests/debuginfo/embedded-visualizer.rs b/tests/debuginfo/embedded-visualizer.rs index cbd8691394d..12d87be7c66 100644 --- a/tests/debuginfo/embedded-visualizer.rs +++ b/tests/debuginfo/embedded-visualizer.rs @@ -1,6 +1,8 @@ //@ compile-flags:-g //@ ignore-lldb //@ ignore-windows-gnu: #128981 +//@ ignore-musl: linker too old in CI +//@ ignore-i586-unknown-linux-gnu: linker too old in CI // === CDB TESTS ================================================================================== -- cgit 1.4.1-3-g733a5