[llvm] [Object] Parsing and dumping of SFrame FDEs (PR #149828)

[Pavel Labath via llvm-commits]

================
@@ -19,24 +19,37 @@ namespace object {
 
 template <endianness E> class SFrameParser {
 public:
-  static Expected<SFrameParser> create(ArrayRef<uint8_t> Contents);
+  static Expected<SFrameParser> create(ArrayRef<uint8_t> Contents,
+                                       uint64_t SectionAddress);
 
   const sframe::Preamble<E> &getPreamble() const { return Header.Preamble; }
   const sframe::Header<E> &getHeader() const { return Header; }
 
+  Expected<ArrayRef<uint8_t>> getAuxHeader() const;
+
   bool usesFixedRAOffset() const {
     return getHeader().ABIArch == sframe::ABI::AMD64EndianLittle;
   }
   bool usesFixedFPOffset() const {
     return false; // Not used in any currently defined ABI.
   }
 
+  using FDERange = ArrayRef<sframe::FuncDescEntry<E>>;
+  Expected<FDERange> fdes() const;
+
+  // Decodes the start address of the given FDE, which must be one of the
+  // objects returned by the `fdes()` function.
+  uint64_t getAbsoluteStartAddress(typename FDERange::iterator FDE) const;
+
 private:
   ArrayRef<uint8_t> Data;
+  uint64_t SectionAddress;
   const sframe::Header<E> &Header;
 
-  SFrameParser(ArrayRef<uint8_t> Data, const sframe::Header<E> &Header)
-      : Data(Data), Header(Header) {}
+  SFrameParser(ArrayRef<uint8_t> Data, uint64_t SectionAddress, const sframe::Header<E> &Header)
+      : Data(Data), SectionAddress(SectionAddress), Header(Header) {}
+
+  uint64_t getFDEBegin() const { return sizeof(Header) + Header.AuxHdrLen + Header.FDEOff; }
----------------
labath wrote:

I'm not sure I understand. The value I linked to is used to locate the FDEs, so if `sfh_fdeoff` is not zero, it will end up looking at the wrong place. Or are you saying that it does not matter *in practice* because the value will always be zero? That, I suppose is true (and I don't see why would anyone use a value other than zero here), but the spec does allow it so I suppose someone *could* do it.

I guess my main question is whether I've implemented the FDE location code correctly.

https://github.com/llvm/llvm-project/pull/149828