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

[Eugene Leviant via llvm-commits]

I had test failures when I used the same scheme for binary output
format. May be something has changed since that time.
I don't use binary output, so I don't have any objections against this change

Thanks,
Eugene.

2016-09-29 19:03 GMT+03:00 Rafael Espíndola <rafael.espindola at gmail.com>:
> 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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