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[Object] Parsing and dumping of SFrame Frame Row Entries #151301

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[Object] Parsing and dumping of SFrame Frame Row Entries
labath Jul 16, 2025
7b64ce4
Merge remote-tracking branch 'origin/main' into sframe2
labath Aug 6, 2025
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labath Aug 6, 2025
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1 change: 1 addition & 0 deletions llvm/include/llvm/BinaryFormat/SFrame.h
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Original file line number Diff line number Diff line change
Expand Up @@ -169,6 +169,7 @@ LLVM_ABI ArrayRef<EnumEntry<FREType>> getFRETypes();
LLVM_ABI ArrayRef<EnumEntry<FDEType>> getFDETypes();
LLVM_ABI ArrayRef<EnumEntry<AArch64PAuthKey>> getAArch64PAuthKeys();
LLVM_ABI ArrayRef<EnumEntry<FREOffset>> getFREOffsets();
LLVM_ABI ArrayRef<EnumEntry<BaseReg>> getBaseRegisters();

} // namespace sframe
} // namespace llvm
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51 changes: 51 additions & 0 deletions llvm/include/llvm/Object/SFrameParser.h
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Expand Up @@ -10,6 +10,7 @@
#define LLVM_OBJECT_SFRAME_H

#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/fallible_iterator.h"
#include "llvm/BinaryFormat/SFrame.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Error.h"
Expand All @@ -19,6 +20,8 @@ namespace llvm {
namespace object {

template <endianness E> class SFrameParser {
class FallibleFREIterator;

public:
static Expected<SFrameParser> create(ArrayRef<uint8_t> Contents,
uint64_t SectionAddress);
Expand All @@ -42,6 +45,21 @@ template <endianness E> class SFrameParser {
// objects returned by the `fdes()` function.
uint64_t getAbsoluteStartAddress(typename FDERange::iterator FDE) const;

struct FrameRowEntry {
uint32_t StartAddress;
sframe::FREInfo<endianness::native> Info;
SmallVector<int32_t, 3> Offsets;
};

using fre_iterator = fallible_iterator<FallibleFREIterator>;
iterator_range<fre_iterator> fres(const sframe::FuncDescEntry<E> &FDE,
Error &Err) const;

std::optional<int32_t> getCFAOffset(const FrameRowEntry &FRE) const;
std::optional<int32_t> getRAOffset(const FrameRowEntry &FRE) const;
std::optional<int32_t> getFPOffset(const FrameRowEntry &FRE) const;
ArrayRef<int32_t> getExtraOffsets(const FrameRowEntry &FRE) const;

private:
ArrayRef<uint8_t> Data;
uint64_t SectionAddress;
Expand All @@ -54,6 +72,39 @@ template <endianness E> class SFrameParser {
uint64_t getFDEBase() const {
return sizeof(Header) + Header.AuxHdrLen + Header.FDEOff;
}

uint64_t getFREBase() const {
return getFDEBase() + Header.NumFDEs * sizeof(sframe::FuncDescEntry<E>);
}
};

template <endianness E> class SFrameParser<E>::FallibleFREIterator {
public:
// NB: This iterator starts out in the before_begin() state. It must be
// ++'ed to reach the first element.
FallibleFREIterator(ArrayRef<uint8_t> Data, sframe::FREType FREType,
uint32_t Idx, uint32_t Size, uint64_t Offset)
: Data(Data), FREType(FREType), Idx(Idx), Size(Size), Offset(Offset) {}

Error inc();
const FrameRowEntry &operator*() const { return FRE; }

friend bool operator==(const FallibleFREIterator &LHS,
const FallibleFREIterator &RHS) {
assert(LHS.Data.data() == RHS.Data.data());
assert(LHS.Data.size() == RHS.Data.size());
assert(LHS.FREType == RHS.FREType);
assert(LHS.Size == RHS.Size);
return LHS.Idx == RHS.Idx;
}

private:
ArrayRef<uint8_t> Data;
sframe::FREType FREType;
uint32_t Idx;
uint32_t Size;
uint64_t Offset;
FrameRowEntry FRE;
};

extern template class LLVM_TEMPLATE_ABI SFrameParser<endianness::big>;
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8 changes: 8 additions & 0 deletions llvm/lib/BinaryFormat/SFrame.cpp
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Expand Up @@ -68,3 +68,11 @@ ArrayRef<EnumEntry<sframe::FREOffset>> sframe::getFREOffsets() {
};
return ArrayRef(FREOffsets);
}

ArrayRef<EnumEntry<sframe::BaseReg>> sframe::getBaseRegisters() {
static constexpr EnumEntry<sframe::BaseReg> BaseRegs[] = {
{"FP", sframe::BaseReg::FP},
{"SP", sframe::BaseReg::SP},
};
return ArrayRef(BaseRegs);
}
Comment on lines +72 to +78
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I'm probably missing something, but why not just have the static local exposed as a constant without the function wrapper?

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If you mean something like:

// SFrame.h
extern ArrayRef<EnumEntry<sframe::BaseReg>> BaseRegisters;
// SFrame.cpp
static constexpr EnumEntry<sframe::BaseReg> BaseRegs[] = ...
ArrayRef<EnumEntry<sframe::BaseReg>> BaseRegisters = BaseRegs;

then I believe that should work (without creating new global constructors or anything). I did it this way because that's how this is implemented elsewhere (BinaryFormat/DXContainer.h, DebugInfo/CodeView/EnumTables.h)

132 changes: 128 additions & 4 deletions llvm/lib/Object/SFrameParser.cpp
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Expand Up @@ -32,14 +32,25 @@ getDataSlice(ArrayRef<uint8_t> Data, uint64_t Offset, uint64_t Size) {
}

template <typename T>
static Expected<const T &> getDataSliceAs(ArrayRef<uint8_t> Data,
uint64_t Offset) {
static Expected<ArrayRef<T>>
getDataSliceAsArrayOf(ArrayRef<uint8_t> Data, uint64_t Offset, uint64_t Count) {
static_assert(std::is_trivial_v<T>);
Expected<ArrayRef<uint8_t>> Slice = getDataSlice(Data, Offset, sizeof(T));
Expected<ArrayRef<uint8_t>> Slice =
getDataSlice(Data, Offset, sizeof(T) * Count);
if (!Slice)
return Slice.takeError();

return *reinterpret_cast<const T *>(Slice->data());
return ArrayRef(reinterpret_cast<const T *>(Slice->data()), Count);
}

template <typename T>
static Expected<const T &> getDataSliceAs(ArrayRef<uint8_t> Data,
uint64_t Offset) {
Expected<ArrayRef<T>> Array = getDataSliceAsArrayOf<T>(Data, Offset, 1);
if (!Array)
return Array.takeError();

return Array->front();
}

template <endianness E>
Expand Down Expand Up @@ -100,6 +111,119 @@ uint64_t SFrameParser<E>::getAbsoluteStartAddress(
return Result;
}

template <typename EndianT>
static Error readArray(ArrayRef<uint8_t> Data, uint64_t Count, uint64_t &Offset,
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Why is this returning an Error rather than an Expected?

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Mainly because it simplifies the caller, which would otherwise need to unpack the Expected and copy/move the value into the larger object. I wouldn't do that for a public interface, but these functions are essentially an implementation detail of FallibleFREIterator::inc(), so I thought that would be okay.

I can that if you feel strongly about it, but I think version looks better.

SmallVectorImpl<int32_t> &Vec) {
Expected<ArrayRef<EndianT>> RawArray =
getDataSliceAsArrayOf<EndianT>(Data, Offset, Count);
if (!RawArray)
return RawArray.takeError();
Offset += Count * sizeof(EndianT);
Vec.resize(Count);
llvm::copy(*RawArray, Vec.begin());
return Error::success();
}

template <typename T, endianness E>
static Error readFRE(ArrayRef<uint8_t> Data, uint64_t &Offset,
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Same question.

typename SFrameParser<E>::FrameRowEntry &FRE) {
Expected<sframe::FrameRowEntry<T, E>> RawFRE =
getDataSliceAs<sframe::FrameRowEntry<T, E>>(Data, Offset);
if (!RawFRE)
return RawFRE.takeError();

Offset += sizeof(*RawFRE);
FRE.StartAddress = RawFRE->StartAddress;
FRE.Info.Info = RawFRE->Info.Info;

switch (FRE.Info.getOffsetSize()) {
case sframe::FREOffset::B1:
return readArray<sframe::detail::packed<int8_t, E>>(
Data, FRE.Info.getOffsetCount(), Offset, FRE.Offsets);
case sframe::FREOffset::B2:
return readArray<sframe::detail::packed<int16_t, E>>(
Data, FRE.Info.getOffsetCount(), Offset, FRE.Offsets);
case sframe::FREOffset::B4:
return readArray<sframe::detail::packed<int32_t, E>>(
Data, FRE.Info.getOffsetCount(), Offset, FRE.Offsets);
default:
return createError("unsupported/unknown offset size");
}
}

template <endianness E> Error SFrameParser<E>::FallibleFREIterator::inc() {
if (++Idx == Size)
return Error::success();

switch (FREType) {
case sframe::FREType::Addr1:
return readFRE<uint8_t, E>(Data, Offset, FRE);
case sframe::FREType::Addr2:
return readFRE<uint16_t, E>(Data, Offset, FRE);
case sframe::FREType::Addr4:
return readFRE<uint32_t, E>(Data, Offset, FRE);
default:
return createError("invalid/unsupported FRE type");
}
}

template <endianness E>
iterator_range<typename SFrameParser<E>::fre_iterator>
SFrameParser<E>::fres(const sframe::FuncDescEntry<E> &FDE, Error &Err) const {
uint64_t Offset = getFREBase() + FDE.StartFREOff;
fre_iterator BeforeBegin = make_fallible_itr(
FallibleFREIterator(Data, FDE.getFREType(), -1, FDE.NumFREs, Offset),
Err);
fre_iterator End = make_fallible_end(
FallibleFREIterator(Data, FDE.getFREType(), FDE.NumFREs, FDE.NumFREs,
/*Offset=*/0));
return {++BeforeBegin, End};
}

static std::optional<int32_t> getOffset(ArrayRef<int32_t> Offsets, size_t Idx) {
if (Offsets.size() > Idx)
return Offsets[Idx];
return std::nullopt;
}

// The interpretation of offsets is ABI-specific. The implementation of this and
// the following functions may need to be adjusted when adding support for a new
// ABI.
template <endianness E>
std::optional<int32_t>
SFrameParser<E>::getCFAOffset(const FrameRowEntry &FRE) const {
return getOffset(FRE.Offsets, 0);
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I'm a little concerned about this and the similar code in the following blocks, mostly because future ABIs/architectures won't necessarily have the same meanings for the different offsets. It's probably sufficient for now to add a comment or two highlighting that all supported ABIs use the specified offset.

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Yeah, I expect that the implementation of these functions will need to change when adding a new ABI. In fact, it looks like the recently updated specification adds support for the s390x architecture/ABI. The offset numbers don't really change, but their interpretation is a lot more complicated (mainly to account for the fact that FP/RA registers can be saved in another register.

That will most likely mean changing the interface (return value) of these functions as well.

I added a comment as requested. I will also look into adding s390x support to make the parser complete.

}

template <endianness E>
std::optional<int32_t>
SFrameParser<E>::getRAOffset(const FrameRowEntry &FRE) const {
if (usesFixedRAOffset())
return Header.CFAFixedRAOffset;
return getOffset(FRE.Offsets, 1);
}

template <endianness E>
std::optional<int32_t>
SFrameParser<E>::getFPOffset(const FrameRowEntry &FRE) const {
if (usesFixedFPOffset())
return Header.CFAFixedFPOffset;
return getOffset(FRE.Offsets, usesFixedRAOffset() ? 1 : 2);
}

template <endianness E>
ArrayRef<int32_t>
SFrameParser<E>::getExtraOffsets(const FrameRowEntry &FRE) const {
size_t UsedOffsets = 1; // CFA
if (!usesFixedRAOffset())
++UsedOffsets;
if (!usesFixedFPOffset())
++UsedOffsets;
if (FRE.Offsets.size() > UsedOffsets)
return ArrayRef(FRE.Offsets).drop_front(UsedOffsets);
return {};
}

template class LLVM_EXPORT_TEMPLATE llvm::object::SFrameParser<endianness::big>;
template class LLVM_EXPORT_TEMPLATE
llvm::object::SFrameParser<endianness::little>;
10 changes: 8 additions & 2 deletions llvm/test/tools/llvm-readobj/ELF/sframe-fde.test
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Expand Up @@ -108,6 +108,8 @@ Sections:
# CASE1-NEXT: }
# CASE1-NEXT: Repetitive block size: 0xDE
# CASE1-NEXT: Padding2: 0xAD
# CASE1-NEXT: FREs [
# CASE1-NEXT: ]
# CASE1-NEXT: }
# CASE1-NEXT: ]
# CASE1-NEXT:}
Expand Down Expand Up @@ -169,6 +171,8 @@ Sections:
# CASE1-NEXT: }
# CASE1-NEXT: Repetitive block size (unused): 0xDE
# CASE1-NEXT: Padding2: 0xAD
# CASE1-NEXT: FREs [
# CASE1-NEXT: ]
# CASE1-NEXT: }
# CASE1-NEXT: ]
# CASE1-NEXT:}
Expand Down Expand Up @@ -196,7 +200,7 @@ Sections:
0x00, 0xde, 0xad, 0x00, # Start Address
0x00, 0x00, 0x01, 0xbe, # Size
0x00, 0x00, 0x00, 0x10, # Start FRE Offset
0x00, 0x00, 0x00, 0x10, # Number of FREs
0x00, 0x00, 0x00, 0x00, # Number of FREs
0x02, 0xde, 0xad, 0x00, # Info, RepSize, Padding2
]
# CASE2-LABEL:SFrame section '.sframe' {
Expand All @@ -223,7 +227,7 @@ Sections:
# CASE2-NEXT: PC: 0xDEAD1C
# CASE2-NEXT: Size: 0x1BE
# CASE2-NEXT: Start FRE Offset: 0x10
# CASE2-NEXT: Num FREs: 16
# CASE2-NEXT: Num FREs: 0
# CASE2-NEXT: Info {
# CASE2-NEXT: FRE Type: Addr4 (0x2)
# CASE2-NEXT: FDE Type: PCInc (0x0)
Expand All @@ -232,6 +236,8 @@ Sections:
# CASE2-NEXT: }
# CASE2-NEXT: Repetitive block size (unused): 0xDE
# CASE2-NEXT: Padding2: 0xAD00
# CASE2-NEXT: FREs [
# CASE2-NEXT: ]
# CASE2-NEXT: }
# CASE2-NEXT: ]
# CASE2-NEXT:}
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