compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs

   1 use crate::common::CodegenCx;
   2 use crate::coverageinfo;
   3 use crate::llvm;
   4
   5 use llvm::coverageinfo::CounterMappingRegion;
   6 use rustc_codegen_ssa::coverageinfo::map::{Counter, CounterExpression};
   7 use rustc_codegen_ssa::traits::{BaseTypeMethods, ConstMethods};
   8 use rustc_data_structures::fx::FxIndexSet;
   9 use rustc_llvm::RustString;
  10 use rustc_middle::mir::coverage::CodeRegion;
  11
  12 use std::ffi::CString;
  13
  14 use tracing::debug;
  15
  16 /// Generates and exports the Coverage Map.
  17 ///
  18 /// This Coverage Map complies with Coverage Mapping Format version 3 (zero-based encoded as 2),
  19 /// as defined at [LLVM Code Coverage Mapping Format](https://github.com/rust-lang/llvm-project/blob/llvmorg-8.0.0/llvm/docs/CoverageMappingFormat.rst#llvm-code-coverage-mapping-format)
  20 /// and published in Rust's current (July 2020) fork of LLVM. This version is supported by the
  21 /// LLVM coverage tools (`llvm-profdata` and `llvm-cov`) bundled with Rust's fork of LLVM.
  22 ///
  23 /// Consequently, Rust's bundled version of Clang also generates Coverage Maps compliant with
  24 /// version 3. Clang's implementation of Coverage Map generation was referenced when implementing
  25 /// this Rust version, and though the format documentation is very explicit and detailed, some
  26 /// undocumented details in Clang's implementation (that may or may not be important) were also
  27 /// replicated for Rust's Coverage Map.
  28 pub fn finalize<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>) {
  29     let function_coverage_map = cx.coverage_context().take_function_coverage_map();
  30     if function_coverage_map.is_empty() {
  31         // This module has no functions with coverage instrumentation
  32         return;
  33     }
  34
  35     let mut mapgen = CoverageMapGenerator::new();
  36
  37     // Encode coverage mappings and generate function records
  38     let mut function_records = Vec::<&'ll llvm::Value>::new();
  39     let coverage_mappings_buffer = llvm::build_byte_buffer(|coverage_mappings_buffer| {
  40         for (instance, function_coverage) in function_coverage_map.into_iter() {
  41             debug!("Generate coverage map for: {:?}", instance);
  42
  43             let mangled_function_name = cx.tcx.symbol_name(instance).to_string();
  44             let function_source_hash = function_coverage.source_hash();
  45             let (expressions, counter_regions) =
  46                 function_coverage.get_expressions_and_counter_regions();
  47
  48             let old_len = coverage_mappings_buffer.len();
  49             mapgen.write_coverage_mappings(expressions, counter_regions, coverage_mappings_buffer);
  50             let mapping_data_size = coverage_mappings_buffer.len() - old_len;
  51             debug_assert!(
  52                 mapping_data_size > 0,
  53                 "Every `FunctionCoverage` should have at least one counter"
  54             );
  55
  56             let function_record = mapgen.make_function_record(
  57                 cx,
  58                 mangled_function_name,
  59                 function_source_hash,
  60                 mapping_data_size,
  61             );
  62             function_records.push(function_record);
  63         }
  64     });
  65
  66     // Encode all filenames referenced by counters/expressions in this module
  67     let filenames_buffer = llvm::build_byte_buffer(|filenames_buffer| {
  68         coverageinfo::write_filenames_section_to_buffer(&mapgen.filenames, filenames_buffer);
  69     });
  70
  71     // Generate the LLVM IR representation of the coverage map and store it in a well-known global
  72     mapgen.save_generated_coverage_map(
  73         cx,
  74         function_records,
  75         filenames_buffer,
  76         coverage_mappings_buffer,
  77     );
  78 }
  79
  80 struct CoverageMapGenerator {
  81     filenames: FxIndexSet<CString>,
  82 }
  83
  84 impl CoverageMapGenerator {
  85     fn new() -> Self {
  86         Self { filenames: FxIndexSet::default() }
  87     }
  88
  89     /// Using the `expressions` and `counter_regions` collected for the current function, generate
  90     /// the `mapping_regions` and `virtual_file_mapping`, and capture any new filenames. Then use
  91     /// LLVM APIs to encode the `virtual_file_mapping`, `expressions`, and `mapping_regions` into
  92     /// the given `coverage_mappings` byte buffer, compliant with the LLVM Coverage Mapping format.
  93     fn write_coverage_mappings(
  94         &mut self,
  95         expressions: Vec<CounterExpression>,
  96         counter_regions: impl Iterator<Item = (Counter, &'a CodeRegion)>,
  97         coverage_mappings_buffer: &RustString,
  98     ) {
  99         let mut counter_regions = counter_regions.collect::<Vec<_>>();
 100         if counter_regions.is_empty() {
 101             return;
 102         }
 103
 104         let mut virtual_file_mapping = Vec::new();
 105         let mut mapping_regions = Vec::new();
 106         let mut current_file_name = None;
 107         let mut current_file_id = 0;
 108
 109         // Convert the list of (Counter, CodeRegion) pairs to an array of `CounterMappingRegion`, sorted
 110         // by filename and position. Capture any new files to compute the `CounterMappingRegion`s
 111         // `file_id` (indexing files referenced by the current function), and construct the
 112         // function-specific `virtual_file_mapping` from `file_id` to its index in the module's
 113         // `filenames` array.
 114         counter_regions.sort_unstable_by_key(|(_counter, region)| *region);
 115         for (counter, region) in counter_regions {
 116             let CodeRegion { file_name, start_line, start_col, end_line, end_col } = *region;
 117             let same_file = current_file_name.as_ref().map_or(false, |p| *p == file_name);
 118             if !same_file {
 119                 if current_file_name.is_some() {
 120                     current_file_id += 1;
 121                 }
 122                 current_file_name = Some(file_name);
 123                 let c_filename = CString::new(file_name.to_string())
 124                     .expect("null error converting filename to C string");
 125                 debug!("  file_id: {} = '{:?}'", current_file_id, c_filename);
 126                 let (filenames_index, _) = self.filenames.insert_full(c_filename);
 127                 virtual_file_mapping.push(filenames_index as u32);
 128             }
 129             mapping_regions.push(CounterMappingRegion::code_region(
 130                 counter,
 131                 current_file_id,
 132                 start_line,
 133                 start_col,
 134                 end_line,
 135                 end_col,
 136             ));
 137         }
 138
 139         // Encode and append the current function's coverage mapping data
 140         coverageinfo::write_mapping_to_buffer(
 141             virtual_file_mapping,
 142             expressions,
 143             mapping_regions,
 144             coverage_mappings_buffer,
 145         );
 146     }
 147
 148     /// Generate and return the function record `Value`
 149     fn make_function_record(
 150         &mut self,
 151         cx: &CodegenCx<'ll, 'tcx>,
 152         mangled_function_name: String,
 153         function_source_hash: u64,
 154         mapping_data_size: usize,
 155     ) -> &'ll llvm::Value {
 156         let name_ref = coverageinfo::compute_hash(&mangled_function_name);
 157         let name_ref_val = cx.const_u64(name_ref);
 158         let mapping_data_size_val = cx.const_u32(mapping_data_size as u32);
 159         let func_hash_val = cx.const_u64(function_source_hash);
 160         cx.const_struct(
 161             &[name_ref_val, mapping_data_size_val, func_hash_val],
 162             /*packed=*/ true,
 163         )
 164     }
 165
 166     /// Combine the filenames and coverage mappings buffers, construct coverage map header and the
 167     /// array of function records, and combine everything into the complete coverage map. Save the
 168     /// coverage map data into the LLVM IR as a static global using a specific, well-known section
 169     /// and name.
 170     fn save_generated_coverage_map(
 171         self,
 172         cx: &CodegenCx<'ll, 'tcx>,
 173         function_records: Vec<&'ll llvm::Value>,
 174         filenames_buffer: Vec<u8>,
 175         mut coverage_mappings_buffer: Vec<u8>,
 176     ) {
 177         // Concatenate the encoded filenames and encoded coverage mappings, and add additional zero
 178         // bytes as-needed to ensure 8-byte alignment.
 179         let mut coverage_size = coverage_mappings_buffer.len();
 180         let filenames_size = filenames_buffer.len();
 181         let remaining_bytes =
 182             (filenames_size + coverage_size) % coverageinfo::COVMAP_VAR_ALIGN_BYTES;
 183         if remaining_bytes > 0 {
 184             let pad = coverageinfo::COVMAP_VAR_ALIGN_BYTES - remaining_bytes;
 185             coverage_mappings_buffer.append(&mut [0].repeat(pad));
 186             coverage_size += pad;
 187         }
 188         let filenames_and_coverage_mappings = [filenames_buffer, coverage_mappings_buffer].concat();
 189         let filenames_and_coverage_mappings_val =
 190             cx.const_bytes(&filenames_and_coverage_mappings[..]);
 191
 192         debug!(
 193             "cov map: n_records = {}, filenames_size = {}, coverage_size = {}, 0-based version = {}",
 194             function_records.len(),
 195             filenames_size,
 196             coverage_size,
 197             coverageinfo::mapping_version()
 198         );
 199
 200         // Create the coverage data header
 201         let n_records_val = cx.const_u32(function_records.len() as u32);
 202         let filenames_size_val = cx.const_u32(filenames_size as u32);
 203         let coverage_size_val = cx.const_u32(coverage_size as u32);
 204         let version_val = cx.const_u32(coverageinfo::mapping_version());
 205         let cov_data_header_val = cx.const_struct(
 206             &[n_records_val, filenames_size_val, coverage_size_val, version_val],
 207             /*packed=*/ false,
 208         );
 209
 210         // Create the function records array
 211         let name_ref_from_u64 = cx.type_i64();
 212         let mapping_data_size_from_u32 = cx.type_i32();
 213         let func_hash_from_u64 = cx.type_i64();
 214         let function_record_ty = cx.type_struct(
 215             &[name_ref_from_u64, mapping_data_size_from_u32, func_hash_from_u64],
 216             /*packed=*/ true,
 217         );
 218         let function_records_val = cx.const_array(function_record_ty, &function_records[..]);
 219
 220         // Create the complete LLVM coverage data value to add to the LLVM IR
 221         let cov_data_val = cx.const_struct(
 222             &[cov_data_header_val, function_records_val, filenames_and_coverage_mappings_val],
 223             /*packed=*/ false,
 224         );
 225
 226         // Save the coverage data value to LLVM IR
 227         coverageinfo::save_map_to_mod(cx, cov_data_val);
 228     }
 229 }