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[ELF] Change the way we compute file offsets

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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

llvm-svn: 282705
This commit is contained in:
Eugene Leviant
2016-09-29 09:20:33 +00:00
parent 71e9e44ae9
commit 3d9abec091
3 changed files with 20 additions and 3 deletions
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9
lld/ELF/OutputSections.h
View File

@@ -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() {}

10
lld/ELF/Writer.cpp
View File

@@ -542,6 +542,8 @@ 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)
Sec->FirstInPtLoad = First;
}
template <class ELFT>
@@ -1190,7 +1192,13 @@ static uintX_t getFileAlignment(uintX_t Off, OutputSectionBase<ELFT> *Sec) {
// 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>

4
lld/test/ELF/linkerscript/outsections-addr.s
View File

@@ -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