[Coverage][WebAssembly] Add initial support for WebAssembly/WASI (#111332)

Currently, WebAssembly/WASI target does not provide direct support for
code coverage.
This patch set fixes several issues to unlock the feature. The main
changes are:

1. Port `compiler-rt/lib/profile` to WebAssembly/WASI.
2. Adjust profile metadata sections for Wasm object file format.
- [CodeGen] Emit `__llvm_covmap` and `__llvm_covfun` as custom sections
instead of data segments.
    - [lld] Align the interval space of custom sections at link time.
- [llvm-cov] Copy misaligned custom section data if the start address is
not aligned.
    - [llvm-cov] Read `__llvm_prf_names` from data segments
3. [clang] Link with profile runtime libraries if requested

See each commit message for more details and rationale.
This is part of the effort to add code coverage support in Wasm target
of Swift toolchain.

1 files changed, 72 insertions, 15 deletions

diff --git a/llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp b/llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp
index bc4e780..461fc43d 100644
--- a/llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp
+++ b/llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp
@@ -18,12 +18,14 @@
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/BinaryFormat/Wasm.h"
 #include "llvm/Object/Archive.h"
 #include "llvm/Object/Binary.h"
 #include "llvm/Object/COFF.h"
 #include "llvm/Object/Error.h"
 #include "llvm/Object/MachOUniversal.h"
 #include "llvm/Object/ObjectFile.h"
+#include "llvm/Object/Wasm.h"
 #include "llvm/ProfileData/InstrProf.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Compression.h"
@@ -894,13 +896,15 @@ static Error readCoverageMappingData(
 Expected<std::unique_ptr<BinaryCoverageReader>>
 BinaryCoverageReader::createCoverageReaderFromBuffer(
     StringRef Coverage, FuncRecordsStorage &&FuncRecords,
+    CoverageMapCopyStorage &&CoverageMap,
     std::unique_ptr<InstrProfSymtab> ProfileNamesPtr, uint8_t BytesInAddress,
     llvm::endianness Endian, StringRef CompilationDir) {
   if (ProfileNamesPtr == nullptr)
     return make_error<CoverageMapError>(coveragemap_error::malformed,
                                         "Caller must provide ProfileNames");
-  std::unique_ptr<BinaryCoverageReader> Reader(new BinaryCoverageReader(
-      std::move(ProfileNamesPtr), std::move(FuncRecords)));
+  std::unique_ptr<BinaryCoverageReader> Reader(
+      new BinaryCoverageReader(std::move(ProfileNamesPtr),
+                               std::move(FuncRecords), std::move(CoverageMap)));
   InstrProfSymtab &ProfileNames = *Reader->ProfileNames;
   StringRef FuncRecordsRef = Reader->FuncRecords->getBuffer();
   if (BytesInAddress == 4 && Endian == llvm::endianness::little) {
@@ -1035,8 +1039,8 @@ loadTestingFormat(StringRef Data, StringRef CompilationDir) {
       MemoryBuffer::getMemBuffer(Data);
 
   return BinaryCoverageReader::createCoverageReaderFromBuffer(
-      CoverageMapping, std::move(CoverageRecords), std::move(ProfileNames),
-      BytesInAddress, Endian, CompilationDir);
+      CoverageMapping, std::move(CoverageRecords), nullptr,
+      std::move(ProfileNames), BytesInAddress, Endian, CompilationDir);
 }
 
 /// Find all sections that match \p IPSK name. There may be more than one if
@@ -1075,6 +1079,53 @@ lookupSections(ObjectFile &OF, InstrProfSectKind IPSK) {
   return Sections;
 }
 
+/// Find a section that matches \p Name and is allocatable at runtime.
+///
+/// Returns the contents of the section and its start offset in the object file.
+static Expected<std::pair<StringRef, uint64_t>>
+lookupAllocatableSection(ObjectFile &OF, InstrProfSectKind IPSK) {
+  // On Wasm, allocatable sections can live only in data segments.
+  if (auto *WOF = dyn_cast<WasmObjectFile>(&OF)) {
+    std::vector<const WasmSegment *> Segments;
+    auto ObjFormat = OF.getTripleObjectFormat();
+    auto Name =
+        getInstrProfSectionName(IPSK, ObjFormat, /*AddSegmentInfo=*/false);
+    for (const auto &DebugName : WOF->debugNames()) {
+      if (DebugName.Type != wasm::NameType::DATA_SEGMENT ||
+          DebugName.Name != Name)
+        continue;
+      if (DebugName.Index >= WOF->dataSegments().size())
+        return make_error<CoverageMapError>(coveragemap_error::malformed);
+      auto &Segment = WOF->dataSegments()[DebugName.Index];
+      Segments.push_back(&Segment);
+    }
+    if (Segments.empty())
+      return make_error<CoverageMapError>(coveragemap_error::no_data_found);
+    if (Segments.size() != 1)
+      return make_error<CoverageMapError>(coveragemap_error::malformed);
+
+    const auto &Segment = *Segments.front();
+    auto &Data = Segment.Data;
+    StringRef Content(reinterpret_cast<const char *>(Data.Content.data()),
+                      Data.Content.size());
+    return std::make_pair(Content, Segment.SectionOffset);
+  }
+
+  // On other object file types, delegate to lookupSections to find the section.
+  auto Sections = lookupSections(OF, IPSK);
+  if (!Sections)
+    return Sections.takeError();
+  if (Sections->size() != 1)
+    return make_error<CoverageMapError>(
+        coveragemap_error::malformed,
+        "the size of coverage mapping section is not one");
+  auto &Section = Sections->front();
+  auto ContentsOrErr = Section.getContents();
+  if (!ContentsOrErr)
+    return ContentsOrErr.takeError();
+  return std::make_pair(*ContentsOrErr, Section.getAddress());
+}
+
 static Expected<std::unique_ptr<BinaryCoverageReader>>
 loadBinaryFormat(std::unique_ptr<Binary> Bin, StringRef Arch,
                  StringRef CompilationDir = "",
@@ -1105,23 +1156,20 @@ loadBinaryFormat(std::unique_ptr<Binary> Bin, StringRef Arch,
 
   // Look for the sections that we are interested in.
   auto ProfileNames = std::make_unique<InstrProfSymtab>();
-  std::vector<SectionRef> NamesSectionRefs;
   // If IPSK_name is not found, fallback to search for IPK_covname, which is
   // used when binary correlation is enabled.
-  auto NamesSection = lookupSections(*OF, IPSK_name);
+  auto NamesSection = lookupAllocatableSection(*OF, IPSK_name);
   if (auto E = NamesSection.takeError()) {
     consumeError(std::move(E));
-    NamesSection = lookupSections(*OF, IPSK_covname);
+    NamesSection = lookupAllocatableSection(*OF, IPSK_covname);
     if (auto E = NamesSection.takeError())
       return std::move(E);
   }
-  NamesSectionRefs = *NamesSection;
 
-  if (NamesSectionRefs.size() != 1)
-    return make_error<CoverageMapError>(
-        coveragemap_error::malformed,
-        "the size of coverage mapping section is not one");
-  if (Error E = ProfileNames->create(NamesSectionRefs.back()))
+  uint64_t NamesAddress;
+  StringRef NamesContent;
+  std::tie(NamesContent, NamesAddress) = *NamesSection;
+  if (Error E = ProfileNames->create(NamesContent, NamesAddress))
     return std::move(E);
 
   auto CoverageSection = lookupSections(*OF, IPSK_covmap);
@@ -1136,6 +1184,15 @@ loadBinaryFormat(std::unique_ptr<Binary> Bin, StringRef Arch,
     return CoverageMappingOrErr.takeError();
   StringRef CoverageMapping = CoverageMappingOrErr.get();
 
+  // If the coverage mapping section is not aligned to 8 bytes, copy it to a
+  // new buffer that is. Wasm format typically has unaligned section contents
+  // because it doesn't have a good way to insert padding bytes.
+  std::unique_ptr<MemoryBuffer> CoverageMapCopy;
+  if (!isAddrAligned(Align(8), CoverageMapping.data())) {
+    CoverageMapCopy = MemoryBuffer::getMemBufferCopy(CoverageMapping);
+    CoverageMapping = CoverageMapCopy->getBuffer();
+  }
+
   // Look for the coverage records section (Version4 only).
   auto CoverageRecordsSections = lookupSections(*OF, IPSK_covfun);
 
@@ -1184,8 +1241,8 @@ loadBinaryFormat(std::unique_ptr<Binary> Bin, StringRef Arch,
     *BinaryID = getBuildID(OF.get());
 
   return BinaryCoverageReader::createCoverageReaderFromBuffer(
-      CoverageMapping, std::move(FuncRecords), std::move(ProfileNames),
-      BytesInAddress, Endian, CompilationDir);
+      CoverageMapping, std::move(FuncRecords), std::move(CoverageMapCopy),
+      std::move(ProfileNames), BytesInAddress, Endian, CompilationDir);
 }
 
 /// Determine whether \p Arch is invalid or empty, given \p Bin.