commit 3a7c2f6f44627ab325a0af706760e53d3f491c76
author Rui Ueyama <ruiu@google.com> Fri Jan 08 00:13:23 2016 +0000
committer Rui Ueyama <ruiu@google.com> Fri Jan 08 00:13:23 2016 +0000
tree d3252d2745e6f565e93fed4a64d84eac560307fa
parent b626231a503258a894eb696363db48d897742c16

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.

llvm-svn: 257119

lld/ELF/InputSection.cpp

diff --git a/lld/ELF/InputSection.cpp b/lld/ELF/InputSection.cpp
index b490793..3e949ff 100644
--- a/lld/ELF/InputSection.cpp
+++ b/lld/ELF/InputSection.cpp
@@ -219,8 +219,13 @@
     } 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)

lld/ELF/Target.cpp

diff --git a/lld/ELF/Target.cpp b/lld/ELF/Target.cpp
index bd302ac..ccc59fd 100644
--- a/lld/ELF/Target.cpp
+++ b/lld/ELF/Target.cpp
@@ -139,7 +139,7 @@
                    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 @@
 
 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::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,

lld/ELF/Target.h

diff --git a/lld/ELF/Target.h b/lld/ELF/Target.h
index 52c2697..dcdd5f8 100644
--- a/lld/ELF/Target.h
+++ b/lld/ELF/Target.h
@@ -58,7 +58,7 @@
                              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;