Add setSymbolAddress plugin API and lit test coverage:

- LinkerWrapper::setSymbolAddress(Symbol, Addr): detaches a defined
  symbol from its fragment and assigns it an absolute (SHN_ABS) value,
  callable during AfterLayout. Limited to data symbols only and ensure
  address range is within that of the target architecture. Annotation
  is shown in the map file for affected symbols.

Signed-off-by: Troy Curtiss <trcurtiss@gmail.com>

Author: tcurtiss

include/eld/Core/LinkerScript.h

@@ -273,6 +273,9 @@ class LinkerScript {
   void removeSymbolOp(plugin::LinkerWrapper *W, eld::Module *M,
                       const ResolveInfo *S);
 
+  void setSymbolAddressOp(plugin::LinkerWrapper *W, eld::Module *M,
+                          const ResolveInfo *S, uint64_t Addr);
+
   void updateRuleOp(plugin::LinkerWrapper *W, eld::Module *M, RuleContainer *R,
                     ELFSection *S, const std::string &Annotation = "");
   void updateLinkStatsOp(plugin::LinkerWrapper *W, eld::Module *M,

include/eld/Core/Module.h

@@ -522,6 +522,9 @@ class Module {
   // ---------------------------resetSymbol support -------------------------
   bool resetSymbol(ResolveInfo *, Fragment *F);
 
+  // ---------------------------setSymbolAddress support ---------------------
+  bool setSymbolAddress(ResolveInfo *, uint64_t Addr);
+
   // ---------------------------ImageLayoutChecksum support------------------
   uint64_t getImageLayoutChecksum() const;
 

include/eld/Diagnostics/PluginDiags.inc

@@ -22,6 +22,14 @@ DIAG(error_failed_to_add_sym_to_chunk, DiagnosticEngine::Error,
      "Failed to add symbol '%0' to chunk")
 DIAG(error_failed_to_reset_symbol, DiagnosticEngine::Error,
      "Failed to reset symbol '%0'")
+DIAG(error_failed_to_set_symbol_address, DiagnosticEngine::Error,
+     "Failed to set address of symbol '%0' defined in '%1'")
+DIAG(error_set_symbol_address_on_function, DiagnosticEngine::Error,
+     "Cannot set address of symbol '%0' defined in '%1' because it is a "
+     "function symbol; setSymbolAddress is only allowed on data symbols")
+DIAG(error_set_symbol_address_out_of_range, DiagnosticEngine::Error,
+     "Cannot set address of symbol '%0' defined in '%1' to 0x%2 because it "
+     "exceeds the maximum address 0x%3 supported by the target")
 DIAG(error_failed_to_insert_rule, DiagnosticEngine::Error,
      "Failed to insert rule")
 DIAG(error_invalid_use, DiagnosticEngine::Error, "Invalid Use")

include/eld/LayoutMap/LDYAML.h

@@ -47,6 +47,7 @@ struct Symbol {
   SymbolScope Scope;
   llvm::yaml::Hex32 Size;
   llvm::yaml::Hex64 Value;
+  std::string SetAddressBy;
 };
 // Display Input file if it is used or not.
 struct InputFile {

include/eld/LayoutMap/LayoutInfo.h

@@ -151,6 +151,9 @@ class LayoutInfo {
 
   typedef llvm::DenseMap<const ResolveInfo *, PluginOp *> RemoveSymbolOpsMapT;
 
+  typedef llvm::DenseMap<const ResolveInfo *, PluginOp *>
+      SetSymbolAddressOpsMapT;
+
   typedef llvm::DenseMap<ELFSection *, std::vector<PluginOp *>> SectionOpsMapT;
 
   typedef llvm::DenseMap<const Fragment *, std::vector<PluginOp *>>
@@ -309,6 +312,9 @@ class LayoutInfo {
 
   void recordRemoveSymbol(plugin::LinkerWrapper *W, RemoveSymbolPluginOp *O);
 
+  void recordSetSymbolAddress(plugin::LinkerWrapper *W,
+                              SetSymbolAddressPluginOp *O);
+
   void recordRelocationData(plugin::LinkerWrapper *W,
                             RelocationDataPluginOp *O);
 
@@ -358,6 +364,10 @@ class LayoutInfo {
 
   const RemoveSymbolOpsMapT &getRemovedSymbols() { return RemovedSymbols; }
 
+  const SetSymbolAddressOpsMapT &getSetSymbolAddressOps() {
+    return SetSymbolAddressOps;
+  }
+
   ChunkOpsMapT &getChunkOps() { return ChunkOps; }
 
   SectionOpsMapT &getSectionOps() { return ChangeOutputSectionOps; }
@@ -431,6 +441,8 @@ class LayoutInfo {
   SectionOpsMapT ChangeOutputSectionOps;
   ChunkOpsMapT ChunkOps;
   RemoveSymbolOpsMapT RemovedSymbols;
+
+  SetSymbolAddressOpsMapT SetSymbolAddressOps;
   llvm::DenseSet<plugin::LinkerWrapper *> Plugins;
   // FIXME: Why do member names here start from underscore?
   // Names starting from an underscore is generally used to

include/eld/LayoutMap/YamlLayoutPrinter.h

@@ -59,6 +59,8 @@ class YamlLayoutPrinter {
   void getTrampolineMap(eld::Module &Module,
                         std::vector<eld::LDYAML::TrampolineInfo> &R);
 
+  std::string getSetAddressByStr(const ResolveInfo *R) const;
+
 private:
   std::vector<CommandLineDefault> Defaults;
   std::string CommandLine;

include/eld/Plugin/PluginActivityLog.h

@@ -56,6 +56,8 @@ class PluginActivityLog {
 
   llvm::json::Object toJSON(const RemoveSymbolPluginOp &P) const;
 
+  llvm::json::Object toJSON(const SetSymbolAddressPluginOp &P) const;
+
   llvm::json::Object toJSON(const RelocationDataPluginOp &P) const;
 
   llvm::json::Object toJSON(const UpdateLinkStatsPluginOp &P) const;

include/eld/Plugin/PluginOp.h

@@ -37,7 +37,8 @@ class PluginOp {
     UpdateRule,
     RelocationData,
     UpdateLinkState,
-    SortInputSectionsForMerging
+    SortInputSectionsForMerging,
+    SetSymbolAddress
   };
 
   explicit PluginOp(plugin::LinkerWrapper *, PluginOpType T,
@@ -67,6 +68,7 @@ class PluginOp {
       ADD_CASE(RelocationData)
       ADD_CASE(UpdateLinkState)
       ADD_CASE(SortInputSectionsForMerging)
+      ADD_CASE(SetSymbolAddress)
     }
 #undef ADD_CASE
     return "Unknown";
@@ -194,6 +196,26 @@ class RemoveSymbolPluginOp : public PluginOp {
   const ResolveInfo *RemovedSymbol;
 };
 
+class SetSymbolAddressPluginOp : public PluginOp {
+public:
+  SetSymbolAddressPluginOp(plugin::LinkerWrapper *W, const eld::ResolveInfo *S,
+                           uint64_t Addr);
+
+  static bool classof(const PluginOp *P) {
+    return P->getPluginOpType() == PluginOpType::SetSymbolAddress;
+  }
+
+  std::string getPluginOpStr() const override { return "SA"; }
+
+  const ResolveInfo *getSymbol() const { return Symbol; }
+
+  uint64_t getAddress() const { return Address; }
+
+private:
+  const ResolveInfo *Symbol;
+  uint64_t Address;
+};
+
 class RelocationDataPluginOp : public PluginOp {
 public:
   RelocationDataPluginOp(plugin::LinkerWrapper *W, const eld::Relocation *R,

include/eld/PluginAPI/Diagnostics.h

@@ -17,6 +17,7 @@ DLL_A_EXPORT DiagnosticEntry::DiagIDType warn_no_section_overrides_found();
 DLL_A_EXPORT DiagnosticEntry::DiagIDType error_failed_to_register_reloc();
 DLL_A_EXPORT DiagnosticEntry::DiagIDType error_failed_to_add_sym_to_chunk();
 DLL_A_EXPORT DiagnosticEntry::DiagIDType error_failed_to_reset_symbol();
+DLL_A_EXPORT DiagnosticEntry::DiagIDType error_failed_to_set_symbol_address();
 DLL_A_EXPORT DiagnosticEntry::DiagIDType error_failed_to_insert_rule();
 DLL_A_EXPORT DiagnosticEntry::DiagIDType error_invalid_use();
 DLL_A_EXPORT DiagnosticEntry::DiagIDType error_empty_data();

include/eld/PluginAPI/LinkerWrapper.h

@@ -571,6 +571,33 @@ class DLL_A_EXPORT LinkerWrapper {
   /// be reset is a defined symbol with an initial value.
   eld::Expected<void> resetSymbol(plugin::Symbol S, Chunk C);
 
+  /// Detach symbol S from its current fragment (if any) and make it an
+  /// absolute symbol with value Addr. The symbol's output section index
+  /// becomes SHN_ABS, and its value is no longer derived from any chunk's
+  /// placement.
+  ///
+  /// Unlike resetSymbol(), this works on already-defined symbols.
+  ///
+  /// \param S Symbol whose address is to be set.
+  /// \param Addr Absolute value to assign to the symbol.
+  ///
+  /// \note This function must only be used in the \em AfterLayout link
+  /// state, i.e. after layout, garbage-collection, and relaxation have
+  /// converged, and before the symbol table and relocations are finalized
+  /// and emitted.
+  ///
+  /// \note Reassigning a symbol's address this way does not change the
+  /// address range that the linker's virtual-address overlap check
+  /// associates with the symbol's original output section. If the new
+  /// address could fall inside another section's address range, declare
+  /// the symbol's output section with the \c INFO, \c COPY, \c DSECT, or
+  /// \c OVERLAY linker script section type. These types are equivalent in
+  /// ELD: each removes the section from the overlap check (and from
+  /// PT_LOAD segment placement) by clearing \c SHF_ALLOC on the section,
+  /// which is recommended whenever the section's addresses are bookkeeping
+  /// only and are not meant to be loaded at runtime.
+  eld::Expected<void> setSymbolAddress(plugin::Symbol S, uint64_t Addr);
+
   /// Create and return a Use for a Chunk, and add it to the Chunk.
   eld::Expected<Use> createAndAddUse(Chunk C, off_t Offset,
                                      uint32_t RelocationType, plugin::Symbol S,