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Simplify relocation offset adjustment.

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Previously, relocation offsets are recalculated for .eh_frame sections
inside the main loop, and that messed up the main loop. This patch
separates that logic into a dedicated class.

llvm-svn: 298785
This commit is contained in:
Rui Ueyama
2017-03-26 02:26:33 +00:00
parent 5eb585836a
commit 08aede362b
1 changed files with 50 additions and 25 deletions
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75
lld/ELF/Relocations.cpp
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@@ -638,6 +638,50 @@ mergeMipsN32RelTypes(uint32_t Type, uint32_t Offset, RelTy *I, RelTy *E) {
return std::make_pair(Type, Processed);
}
// .eh_frame sections are mergeable input sections, so their input
// offsets are not linearly mapped to output section. For each input
// offset, we need to find a section piece containing the offset and
// add the piece's base address to the input offset to compute the
// output offset. That isn't cheap.
//
// This class is to speed up the offset computation. When we process
// relocations, we access offsets in the monotonically increasing
// order. So we can optimize for that access pattern.
//
// For sections other than .eh_frame, this class doesn't do anything.
namespace {
class OffsetGetter {
public:
explicit OffsetGetter(InputSectionBase &Sec) {
if (auto *Eh = dyn_cast<EhInputSection>(&Sec)) {
P = Eh->Pieces;
Size = Eh->Pieces.size();
}
}
uint64_t get(uint64_t Off) {
if (P.empty())
return Off;
while (I != Size && P[I].InputOff + P[I].size() <= Off)
++I;
if (I == Size)
return Off;
assert(P[I].InputOff <= Off && "Relocation not in any piece");
// Offset -1 means that the piece is dead (i.e. garbage collected).
if (P[I].OutputOff == -1)
return -1;
return P[I].OutputOff + Off - P[I].InputOff;
}
private:
ArrayRef<EhSectionPiece> P;
size_t I = 0;
size_t Size;
};
}
// The reason we have to do this early scan is as follows
// * To mmap the output file, we need to know the size
// * For that, we need to know how many dynamic relocs we will have.
@@ -666,13 +710,7 @@ static void scanRelocs(InputSectionBase &C, ArrayRef<RelTy> Rels) {
const elf::ObjectFile<ELFT> *File = C.getFile<ELFT>();
ArrayRef<uint8_t> SectionData = C.Data;
const uint8_t *Buf = SectionData.begin();
ArrayRef<EhSectionPiece> Pieces;
if (auto *Eh = dyn_cast<EhInputSection>(&C))
Pieces = Eh->Pieces;
ArrayRef<EhSectionPiece>::iterator PieceI = Pieces.begin();
ArrayRef<EhSectionPiece>::iterator PieceE = Pieces.end();
OffsetGetter GetOffset(C);
for (auto I = Rels.begin(), E = Rels.end(); I != E; ++I) {
const RelTy &RI = *I;
@@ -686,6 +724,11 @@ static void scanRelocs(InputSectionBase &C, ArrayRef<RelTy> Rels) {
I += Processed;
}
// Compute the offset of this section in the output section.
uintX_t Offset = GetOffset.get(RI.r_offset);
if (Offset == uintX_t(-1))
continue;
// Report undefined symbols. The fact that we report undefined
// symbols here means that we report undefined symbols only when
// they have relocations pointing to them. We don't care about
@@ -705,24 +748,6 @@ static void scanRelocs(InputSectionBase &C, ArrayRef<RelTy> Rels) {
if (ErrorCount)
continue;
// Skip a relocation that points to a dead piece
// in a eh_frame section.
while (PieceI != PieceE &&
(PieceI->InputOff + PieceI->size() <= RI.r_offset))
++PieceI;
// Compute the offset of this section in the output section. We do it here
// to try to compute it only once.
uintX_t Offset;
if (PieceI != PieceE) {
assert(PieceI->InputOff <= RI.r_offset && "Relocation not in any piece");
if (PieceI->OutputOff == -1)
continue;
Offset = PieceI->OutputOff + RI.r_offset - PieceI->InputOff;
} else {
Offset = RI.r_offset;
}
// This relocation does not require got entry, but it is relative to got and
// needs it to be created. Here we request for that.
if (isRelExprOneOf<R_GOTONLY_PC, R_GOTONLY_PC_FROM_END, R_GOTREL,