[ELF][ARM] Use SyntheticSections for Thunks

    
Thunks are now implemented by redirecting the relocation to the
symbol S, to a symbol TS in a Thunk. The Thunk will transfer control
to S. This has the following implications:
- All the side-effects of Thunks happen within createThunks()
- Thunks are no longer stored in InputSections and Symbols no longer
  need to hold a pointer to a Thunk
- The synthetic Thunk sections need to be merged into OutputSections
    
This implementation is almost a direct conversion of the existing
Thunks with the following exceptions:
- Mips LA25 Thunks are placed before the InputSection that defines
  the symbol that needs a Thunk.
- All ARM Thunks are placed at the end of the OutputSection of the
  first caller to the Thunk.
    
Range extension Thunks are not supported yet so it is optimistically
assumed that all Thunks can be reused.

Differential Revision:  https://reviews.llvm.org/D29129

llvm-svn: 293283

1 files changed, 5 insertions, 10 deletions

diff --git a/lld/ELF/Target.h b/lld/ELF/Target.h
index 76db720d4da..e439b20f852 100644
--- a/lld/ELF/Target.h
+++ b/lld/ELF/Target.h
@@ -41,8 +41,8 @@ public:
   virtual void writePlt(uint8_t *Buf, uint64_t GotEntryAddr,
                         uint64_t PltEntryAddr, int32_t Index,
                         unsigned RelOff) const {}
-  virtual void addPltHeaderSymbols(InputSectionData* IS) const {}
-  virtual void addPltSymbols(InputSectionData* IS, uint64_t Off) const {}
+  virtual void addPltHeaderSymbols(InputSectionData *IS) const {}
+  virtual void addPltSymbols(InputSectionData *IS, uint64_t Off) const {}
   // Returns true if a relocation only uses the low bits of a value such that
   // all those bits are in in the same page. For example, if the relocation
   // only uses the low 12 bits in a system with 4k pages. If this is true, the
@@ -51,14 +51,9 @@ public:
   virtual bool usesOnlyLowPageBits(uint32_t Type) const;
 
   // Decide whether a Thunk is needed for the relocation from File
-  // targeting S. Returns one of:
-  // Expr if there is no Thunk required
-  // R_THUNK_ABS if thunk is required and expression is absolute
-  // R_THUNK_PC if thunk is required and expression is pc rel
-  // R_THUNK_PLT_PC if thunk is required to PLT entry and expression is pc rel
-  virtual RelExpr getThunkExpr(RelExpr Expr, uint32_t RelocType,
-                               const InputFile *File,
-                               const SymbolBody &S) const;
+  // targeting S.
+  virtual bool needsThunk(RelExpr Expr, uint32_t RelocType,
+                          const InputFile *File, const SymbolBody &S) const;
   virtual RelExpr getRelExpr(uint32_t Type, const SymbolBody &S) const = 0;
   virtual void relocateOne(uint8_t *Loc, uint32_t Type, uint64_t Val) const = 0;
   virtual ~TargetInfo();