llvm/lib/ExecutionEngine/JITLink/DWARFRecordSectionSplitter.cpp

   1 //===-------- JITLink_DWARFRecordSectionSplitter.cpp - JITLink-------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "llvm/ExecutionEngine/JITLink/DWARFRecordSectionSplitter.h"
  10 #include "llvm/Support/BinaryStreamReader.h"
  11
  12 #define DEBUG_TYPE "jitlink"
  13
  14 namespace llvm {
  15 namespace jitlink {
  16
  17 DWARFRecordSectionSplitter::DWARFRecordSectionSplitter(StringRef SectionName)
  18     : SectionName(SectionName) {}
  19
  20 Error DWARFRecordSectionSplitter::operator()(LinkGraph &G) {
  21   auto *Section = G.findSectionByName(SectionName);
  22
  23   if (!Section) {
  24     LLVM_DEBUG({
  25       dbgs() << "DWARFRecordSectionSplitter: No " << SectionName
  26              << " section. Nothing to do\n";
  27     });
  28     return Error::success();
  29   }
  30
  31   LLVM_DEBUG({
  32     dbgs() << "DWARFRecordSectionSplitter: Processing " << SectionName
  33            << "...\n";
  34   });
  35
  36   DenseMap<Block *, LinkGraph::SplitBlockCache> Caches;
  37
  38   {
  39     // Pre-build the split caches.
  40     for (auto *B : Section->blocks())
  41       Caches[B] = LinkGraph::SplitBlockCache::value_type();
  42     for (auto *Sym : Section->symbols())
  43       Caches[&Sym->getBlock()]->push_back(Sym);
  44     for (auto *B : Section->blocks())
  45       llvm::sort(*Caches[B], [](const Symbol *LHS, const Symbol *RHS) {
  46         return LHS->getOffset() > RHS->getOffset();
  47       });
  48   }
  49
  50   // Iterate over blocks (we do this by iterating over Caches entries rather
  51   // than Section->blocks() as we will be inserting new blocks along the way,
  52   // which would invalidate iterators in the latter sequence.
  53   for (auto &KV : Caches) {
  54     auto &B = *KV.first;
  55     auto &BCache = KV.second;
  56     if (auto Err = processBlock(G, B, BCache))
  57       return Err;
  58   }
  59
  60   return Error::success();
  61 }
  62
  63 Error DWARFRecordSectionSplitter::processBlock(
  64     LinkGraph &G, Block &B, LinkGraph::SplitBlockCache &Cache) {
  65   LLVM_DEBUG(dbgs() << "  Processing block at " << B.getAddress() << "\n");
  66
  67   // Section should not contain zero-fill blocks.
  68   if (B.isZeroFill())
  69     return make_error<JITLinkError>("Unexpected zero-fill block in " +
  70                                     SectionName + " section");
  71
  72   if (B.getSize() == 0) {
  73     LLVM_DEBUG(dbgs() << "    Block is empty. Skipping.\n");
  74     return Error::success();
  75   }
  76
  77   BinaryStreamReader BlockReader(
  78       StringRef(B.getContent().data(), B.getContent().size()),
  79       G.getEndianness());
  80
  81   while (true) {
  82     uint64_t RecordStartOffset = BlockReader.getOffset();
  83
  84     LLVM_DEBUG({
  85       dbgs() << "    Processing CFI record at "
  86              << formatv("{0:x16}", B.getAddress()) << "\n";
  87     });
  88
  89     uint32_t Length;
  90     if (auto Err = BlockReader.readInteger(Length))
  91       return Err;
  92     if (Length != 0xffffffff) {
  93       if (auto Err = BlockReader.skip(Length))
  94         return Err;
  95     } else {
  96       uint64_t ExtendedLength;
  97       if (auto Err = BlockReader.readInteger(ExtendedLength))
  98         return Err;
  99       if (auto Err = BlockReader.skip(ExtendedLength))
 100         return Err;
 101     }
 102
 103     // If this was the last block then there's nothing to split
 104     if (BlockReader.empty()) {
 105       LLVM_DEBUG(dbgs() << "      Extracted " << B << "\n");
 106       return Error::success();
 107     }
 108
 109     uint64_t BlockSize = BlockReader.getOffset() - RecordStartOffset;
 110     auto &NewBlock = G.splitBlock(B, BlockSize, &Cache);
 111     (void)NewBlock;
 112     LLVM_DEBUG(dbgs() << "      Extracted " << NewBlock << "\n");
 113   }
 114 }
 115
 116 } // namespace jitlink
 117 } // namespace llvm