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

[Rafael Espíndola via llvm-commits]

Small question, why do we have to treat --obinary differently?

All tests pass with the attached file.

Cheers,
Rafael


On 29 September 2016 at 08:33, Rafael Espíndola
<rafael.espindola at gmail.com> wrote:
> Thanks!
>
> On 29 September 2016 at 02:20, Eugene Leviant via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
>> 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
>>
>>
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-------------- next part --------------
diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index 7774507..239d45a 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -544,7 +544,7 @@ void PhdrEntry<ELFT>::add(OutputSectionBase<ELFT> *Sec) {
   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)
+  if (H.p_type == PT_LOAD)
     Sec->FirstInPtLoad = First;
 }