[lld] r282705 - [ELF] Change the way we compute file offsets

[Eugene Leviant via llvm-commits]

Author: evgeny777
Date: Thu Sep 29 04:20:33 2016
New Revision: 282705

URL: http://llvm.org/viewvc/llvm-project?rev=282705&view=rev
Log:
[ELF] Change the way we compute file offsets 

If we two sections reside in the same PT_LOAD segment,
we compute second section using the following formula:
Off2 = Off1 + VA2 - VA1. This allows OS kernel allocating
sections correctly when loading an image.

Differential revision: https://reviews.llvm.org/D25014

Modified:
    lld/trunk/ELF/OutputSections.h
    lld/trunk/ELF/Writer.cpp
    lld/trunk/test/ELF/linkerscript/outsections-addr.s

Modified: lld/trunk/ELF/OutputSections.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.h?rev=282705&r1=282704&r2=282705&view=diff
==============================================================================
--- lld/trunk/ELF/OutputSections.h (original)
+++ lld/trunk/ELF/OutputSections.h Thu Sep 29 04:20:33 2016
@@ -77,6 +77,7 @@ public:
   void setVA(uintX_t VA) { Header.sh_addr = VA; }
   uintX_t getVA() const { return Header.sh_addr; }
   void setFileOffset(uintX_t Off) { Header.sh_offset = Off; }
+  uintX_t getFileOffset() { return Header.sh_offset; }
   void setSHName(unsigned Val) { Header.sh_name = Val; }
   void writeHeaderTo(Elf_Shdr *SHdr);
   StringRef getName() { return Name; }
@@ -108,6 +109,14 @@ public:
   // Typically the first section of each PT_LOAD segment has this flag.
   bool PageAlign = false;
 
+  // Pointer to the first section in PT_LOAD segment, which this section
+  // also resides in. This field is used to correctly compute file offset
+  // of a section. When two sections share the same load segment, difference
+  // between their file offsets should be equal to difference between their
+  // virtual addresses. To compute some section offset we use the following
+  // formula: Off = Off_first + VA - VA_first.
+  OutputSectionBase<ELFT> *FirstInPtLoad = nullptr;
+
   virtual void finalize() {}
   virtual void finalizePieces() {}
   virtual void assignOffsets() {}

Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=282705&r1=282704&r2=282705&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Thu Sep 29 04:20:33 2016
@@ -542,6 +542,8 @@ void PhdrEntry<ELFT>::add(OutputSectionB
   if (!First)
     First = Sec;
   H.p_align = std::max<typename ELFT::uint>(H.p_align, Sec->getAlignment());
+  if (H.p_type == PT_LOAD && !Config->OFormatBinary)
+    Sec->FirstInPtLoad = First;
 }
 
 template <class ELFT>
@@ -1190,7 +1192,13 @@ static uintX_t getFileAlignment(uintX_t
   // and does not need any other offset adjusting.
   if (Config->Relocatable || !(Sec->getFlags() & SHF_ALLOC))
     return Off;
-  return alignTo(Off, Config->MaxPageSize, Sec->getVA());
+
+  OutputSectionBase<ELFT> *First = Sec->FirstInPtLoad;
+  // If two sections share the same PT_LOAD the file offset is calculated using
+  // this formula: Off2 = Off1 + (VA2 - VA1).
+  if (!First || Sec == First)
+    return alignTo(Off, Target->MaxPageSize, Sec->getVA());
+  return First->getFileOffset() + Sec->getVA() - First->getVA();
 }
 
 template <class ELFT, class uintX_t>

Modified: lld/trunk/test/ELF/linkerscript/outsections-addr.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/linkerscript/outsections-addr.s?rev=282705&r1=282704&r2=282705&view=diff
==============================================================================
--- lld/trunk/test/ELF/linkerscript/outsections-addr.s (original)
+++ lld/trunk/test/ELF/linkerscript/outsections-addr.s Thu Sep 29 04:20:33 2016
@@ -81,7 +81,7 @@
 #CHECK:      SHF_ALLOC
 #CHECK:    ]
 #CHECK:    Address: 0x4008
-#CHECK:    Offset: 0x2008
+#CHECK:    Offset: 0x3008
 #CHECK:    Size: 8
 #CHECK:    Link: 0
 #CHECK:    Info: 0
@@ -96,7 +96,7 @@
 #CHECK:      SHF_ALLOC
 #CHECK:    ]
 #CHECK:    Address: 0x5010
-#CHECK:    Offset: 0x2010
+#CHECK:    Offset: 0x4010
 #CHECK:    Size: 8
 #CHECK:    Link: 0
 #CHECK:    Info: 0