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[JITLink] Allow multiple relocations at same offset in EHFrameEdgeFix…
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…er (#68252)

The pass only requires that it can determine a uniquely identified
target at some offsets. Multiple relocations at the same offset are fine
otherwise and will be required when adding exception handling support
for RISC-V.
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@hahnjo
hahnjo committed Oct 22, 2023
1 parent 9f3b06d commit 508a697
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Showing 2 changed files with 41 additions and 21 deletions.
46 changes: 31 additions & 15 deletions llvm/lib/ExecutionEngine/JITLink/EHFrameSupport.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -126,16 +126,23 @@ Error EHFrameEdgeFixer::processBlock(ParseContext &PC, Block &B) {
}

// Find the offsets of any existing edges from this block.
BlockEdgeMap BlockEdges;
BlockEdgesInfo BlockEdges;
for (auto &E : B.edges())
if (E.isRelocation()) {
if (BlockEdges.count(E.getOffset()))
return make_error<JITLinkError>(
"Multiple relocations at offset " +
formatv("{0:x16}", E.getOffset()) + " in " + EHFrameSectionName +
" block at address " + formatv("{0:x16}", B.getAddress()));

BlockEdges[E.getOffset()] = EdgeTarget(E);
// Check if we already saw more than one relocation at this offset.
if (BlockEdges.Multiple.contains(E.getOffset()))
continue;

// Otherwise check if we previously had exactly one relocation at this
// offset. If so, we now have a second one and move it from the TargetMap
// into the Multiple set.
auto It = BlockEdges.TargetMap.find(E.getOffset());
if (It != BlockEdges.TargetMap.end()) {
BlockEdges.TargetMap.erase(It);
BlockEdges.Multiple.insert(E.getOffset());
} else {
BlockEdges.TargetMap[E.getOffset()] = EdgeTarget(E);
}
}

BinaryStreamReader BlockReader(
Expand Down Expand Up @@ -172,7 +179,7 @@ Error EHFrameEdgeFixer::processBlock(ParseContext &PC, Block &B) {

Error EHFrameEdgeFixer::processCIE(ParseContext &PC, Block &B,
size_t CIEDeltaFieldOffset,
const BlockEdgeMap &BlockEdges) {
const BlockEdgesInfo &BlockEdges) {

LLVM_DEBUG(dbgs() << " Record is CIE\n");

Expand Down Expand Up @@ -285,7 +292,7 @@ Error EHFrameEdgeFixer::processCIE(ParseContext &PC, Block &B,
Error EHFrameEdgeFixer::processFDE(ParseContext &PC, Block &B,
size_t CIEDeltaFieldOffset,
uint32_t CIEDelta,
const BlockEdgeMap &BlockEdges) {
const BlockEdgesInfo &BlockEdges) {
LLVM_DEBUG(dbgs() << " Record is FDE\n");

orc::ExecutorAddr RecordAddress = B.getAddress();
Expand All @@ -303,12 +310,17 @@ Error EHFrameEdgeFixer::processFDE(ParseContext &PC, Block &B,

{
// Process the CIE pointer field.
auto CIEEdgeItr = BlockEdges.find(CIEDeltaFieldOffset);
if (BlockEdges.Multiple.contains(CIEDeltaFieldOffset))
return make_error<JITLinkError>(
"CIE pointer field already has multiple edges at " +
formatv("{0:x16}", RecordAddress + CIEDeltaFieldOffset));

auto CIEEdgeItr = BlockEdges.TargetMap.find(CIEDeltaFieldOffset);

orc::ExecutorAddr CIEAddress =
RecordAddress + orc::ExecutorAddrDiff(CIEDeltaFieldOffset) -
orc::ExecutorAddrDiff(CIEDelta);
if (CIEEdgeItr == BlockEdges.end()) {
if (CIEEdgeItr == BlockEdges.TargetMap.end()) {
LLVM_DEBUG({
dbgs() << " Adding edge at "
<< (RecordAddress + CIEDeltaFieldOffset)
Expand Down Expand Up @@ -497,7 +509,7 @@ Error EHFrameEdgeFixer::skipEncodedPointer(uint8_t PointerEncoding,
}

Expected<Symbol *> EHFrameEdgeFixer::getOrCreateEncodedPointerEdge(
ParseContext &PC, const BlockEdgeMap &BlockEdges, uint8_t PointerEncoding,
ParseContext &PC, const BlockEdgesInfo &BlockEdges, uint8_t PointerEncoding,
BinaryStreamReader &RecordReader, Block &BlockToFix,
size_t PointerFieldOffset, const char *FieldName) {
using namespace dwarf;
Expand All @@ -508,8 +520,8 @@ Expected<Symbol *> EHFrameEdgeFixer::getOrCreateEncodedPointerEdge(
// If there's already an edge here then just skip the encoded pointer and
// return the edge's target.
{
auto EdgeI = BlockEdges.find(PointerFieldOffset);
if (EdgeI != BlockEdges.end()) {
auto EdgeI = BlockEdges.TargetMap.find(PointerFieldOffset);
if (EdgeI != BlockEdges.TargetMap.end()) {
LLVM_DEBUG({
dbgs() << " Existing edge at "
<< (BlockToFix.getAddress() + PointerFieldOffset) << " to "
Expand All @@ -522,6 +534,10 @@ Expected<Symbol *> EHFrameEdgeFixer::getOrCreateEncodedPointerEdge(
return std::move(Err);
return EdgeI->second.Target;
}

if (BlockEdges.Multiple.contains(PointerFieldOffset))
return make_error<JITLinkError>("Multiple relocations at offset " +
formatv("{0:x16}", PointerFieldOffset));
}

// Switch absptr to corresponding udata encoding.
Expand Down
16 changes: 10 additions & 6 deletions llvm/lib/ExecutionEngine/JITLink/EHFrameSupportImpl.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -60,7 +60,11 @@ class EHFrameEdgeFixer {
Edge::AddendT Addend = 0;
};

using BlockEdgeMap = DenseMap<Edge::OffsetT, EdgeTarget>;
struct BlockEdgesInfo {
DenseMap<Edge::OffsetT, EdgeTarget> TargetMap;
DenseSet<Edge::OffsetT> Multiple;
};

using CIEInfosMap = DenseMap<orc::ExecutorAddr, CIEInformation>;

struct ParseContext {
Expand All @@ -82,9 +86,9 @@ class EHFrameEdgeFixer {

Error processBlock(ParseContext &PC, Block &B);
Error processCIE(ParseContext &PC, Block &B, size_t CIEDeltaFieldOffset,
const BlockEdgeMap &BlockEdges);
const BlockEdgesInfo &BlockEdges);
Error processFDE(ParseContext &PC, Block &B, size_t CIEDeltaFieldOffset,
uint32_t CIEDelta, const BlockEdgeMap &BlockEdges);
uint32_t CIEDelta, const BlockEdgesInfo &BlockEdges);

Expected<AugmentationInfo>
parseAugmentationString(BinaryStreamReader &RecordReader);
Expand All @@ -94,9 +98,9 @@ class EHFrameEdgeFixer {
Error skipEncodedPointer(uint8_t PointerEncoding,
BinaryStreamReader &RecordReader);
Expected<Symbol *> getOrCreateEncodedPointerEdge(
ParseContext &PC, const BlockEdgeMap &BlockEdges, uint8_t PointerEncoding,
BinaryStreamReader &RecordReader, Block &BlockToFix,
size_t PointerFieldOffset, const char *FieldName);
ParseContext &PC, const BlockEdgesInfo &BlockEdges,
uint8_t PointerEncoding, BinaryStreamReader &RecordReader,
Block &BlockToFix, size_t PointerFieldOffset, const char *FieldName);

Expected<Symbol &> getOrCreateSymbol(ParseContext &PC,
orc::ExecutorAddr Addr);
Expand Down

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