[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:

@ibhagatgnu, I'm a little but unsure about this part. This is the interpretation I get from the specification, and I think it matches [this](https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=libsframe/sframe.c;h=824d1fd7ed99e28f07f2e3f935080228efa38b24;hb=HEAD#l497) endiannes-flipping code in libsframe. However, that's not what happens in the actual [parsing code](https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=libsframe/sframe.c;h=824d1fd7ed99e28f07f2e3f935080228efa38b24;hb=HEAD#l961). Can I assume the last part to be an omission/bug?

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