[lld] r257119 - ELF: Simplify Target::isSizeReloc and add comments.

[Rui Ueyama via llvm-commits]

Author: ruiu
Date: Thu Jan  7 18:13:23 2016
New Revision: 257119

URL: http://llvm.org/viewvc/llvm-project?rev=257119&view=rev
Log:
ELF: Simplify Target::isSizeReloc and add comments.

All non-trivial relocation decisions need explanations like this
to help readers understand not only how relocations are handled but
why they are handled these ways. This is a start.

Modified:
    lld/trunk/ELF/InputSection.cpp
    lld/trunk/ELF/Target.cpp
    lld/trunk/ELF/Target.h

Modified: lld/trunk/ELF/InputSection.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputSection.cpp?rev=257119&r1=257118&r2=257119&view=diff
==============================================================================
--- lld/trunk/ELF/InputSection.cpp (original)
+++ lld/trunk/ELF/InputSection.cpp Thu Jan  7 18:13:23 2016
@@ -219,8 +219,13 @@ void InputSectionBase<ELFT>::relocate(ui
     } else if (!Target->needsCopyRel(Type, *Body) &&
                isa<SharedSymbol<ELFT>>(*Body)) {
       continue;
-    } else if (Target->isTlsDynReloc(Type, *Body) ||
-               Target->isSizeDynReloc(Type, *Body)) {
+    } else if (Target->isTlsDynReloc(Type, *Body)) {
+      continue;
+    } else if (Target->isSizeReloc(Type) && canBePreempted(Body, false)) {
+      // A SIZE relocation is supposed to set a symbol size, but if a symbol
+      // can be preempted, the size at runtime may be different than link time.
+      // If that's the case, we leave the field alone rather than filling it
+      // with a possibly incorrect value.
       continue;
     } else if (Config->EMachine == EM_MIPS) {
       if (Type == R_MIPS_HI16 && Body == Config->MipsGpDisp)

Modified: lld/trunk/ELF/Target.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Target.cpp?rev=257119&r1=257118&r2=257119&view=diff
==============================================================================
--- lld/trunk/ELF/Target.cpp (original)
+++ lld/trunk/ELF/Target.cpp Thu Jan  7 18:13:23 2016
@@ -139,7 +139,7 @@ public:
                    uint8_t *PairedLoc = nullptr) const override;
   bool isRelRelative(uint32_t Type) const override;
   bool isTlsOptimized(unsigned Type, const SymbolBody *S) const override;
-  bool isSizeDynReloc(uint32_t Type, const SymbolBody &S) const override;
+  bool isSizeReloc(uint32_t Type) const override;
   unsigned relocateTlsOptimize(uint8_t *Loc, uint8_t *BufEnd, uint32_t Type,
                                uint64_t P, uint64_t SA,
                                const SymbolBody &S) const override;
@@ -269,9 +269,7 @@ unsigned TargetInfo::getPltRefReloc(unsi
 
 bool TargetInfo::isRelRelative(uint32_t Type) const { return true; }
 
-bool TargetInfo::isSizeDynReloc(uint32_t Type, const SymbolBody &S) const {
-  return false;
-}
+bool TargetInfo::isSizeReloc(uint32_t Type) const { return false; }
 
 unsigned TargetInfo::relocateTlsOptimize(uint8_t *Loc, uint8_t *BufEnd,
                                          uint32_t Type, uint64_t P, uint64_t SA,
@@ -722,10 +720,8 @@ bool X86_64TargetInfo::isRelRelative(uin
   }
 }
 
-bool X86_64TargetInfo::isSizeDynReloc(uint32_t Type,
-                                      const SymbolBody &S) const {
-  return (Type == R_X86_64_SIZE32 || Type == R_X86_64_SIZE64) &&
-         canBePreempted(&S, false);
+bool X86_64TargetInfo::isSizeReloc(uint32_t Type) const {
+  return Type == R_X86_64_SIZE32 || Type == R_X86_64_SIZE64;
 }
 
 bool X86_64TargetInfo::isTlsOptimized(unsigned Type,

Modified: lld/trunk/ELF/Target.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Target.h?rev=257119&r1=257118&r2=257119&view=diff
==============================================================================
--- lld/trunk/ELF/Target.h (original)
+++ lld/trunk/ELF/Target.h Thu Jan  7 18:13:23 2016
@@ -58,7 +58,7 @@ public:
                              uint64_t GotEntryAddr, uint64_t PltEntryAddr,
                              int32_t Index, unsigned RelOff) const = 0;
   virtual bool isRelRelative(uint32_t Type) const;
-  virtual bool isSizeDynReloc(uint32_t Type, const SymbolBody &S) const;
+  virtual bool isSizeReloc(uint32_t Type) const;
   virtual bool relocNeedsDynRelative(unsigned Type) const { return false; }
   virtual bool relocNeedsGot(uint32_t Type, const SymbolBody &S) const = 0;
   virtual bool relocNeedsPlt(uint32_t Type, const SymbolBody &S) const = 0;