[lld] r294816 - Create only one section symbol per section.
Rafael Espindola via llvm-commits
llvm-commits at lists.llvm.org
Fri Feb 10 17:40:50 PST 2017
Author: rafael
Date: Fri Feb 10 19:40:49 2017
New Revision: 294816
URL: http://llvm.org/viewvc/llvm-project?rev=294816&view=rev
Log:
Create only one section symbol per section.
Unfortunately some consumers of our .o files produced with -r expect
only one section symbol per section. That is true of at least of go's
own linker.
Combining them is a somewhat convoluted process. We have to create a
symbol for every section since we don't know which ones will be
needed. The relocation sections also have to be written first to
handle the Elf_Rel addend.
I did consider a completely different approach:
We could remove the -r special case of relocation sections when
reading. We would instead have a copyRelocs function that is used
instead of scanRelocs. It would create a DynamicReloc for each
relocation and a RelocationSection for each input relocation section.
A complication of such change is that DynamicReloc would have to take
a section index and a input section instead of a symbol since with
-emit-relocs some DynamicReloc would hold relocations referring to the
dynamic symbol table and other to the static symbol table.
That would be a pretty big change, and if we do it it is probably
better to do it as a refactoring.
Added:
lld/trunk/test/ELF/relocatable-section-symbol.s
Modified:
lld/trunk/ELF/InputSection.cpp
lld/trunk/ELF/SyntheticSections.cpp
lld/trunk/ELF/Writer.cpp
lld/trunk/test/ELF/emit-relocs.s
lld/trunk/test/ELF/mips-sto-pic-flag.s
lld/trunk/test/ELF/relocatable-bss.s
Modified: lld/trunk/ELF/InputSection.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputSection.cpp?rev=294816&r1=294815&r2=294816&view=diff
==============================================================================
--- lld/trunk/ELF/InputSection.cpp (original)
+++ lld/trunk/ELF/InputSection.cpp Fri Feb 10 19:40:49 2017
@@ -236,6 +236,22 @@ void InputSection<ELFT>::copyRelocations
if (Config->Rela)
P->r_addend = getAddend<ELFT>(Rel);
+ if (Body.Type == STT_SECTION) {
+ // We combine multiple section symbols into only one per
+ // section. This means we have to update the addend. That is
+ // trivial for Elf_Rela, but for Elf_Rel we have to write to the
+ // section data. We do that by adding to the Relocation vector.
+ if (Config->Rela) {
+ P->r_addend += Body.getVA<ELFT>() -
+ cast<DefinedRegular<ELFT>>(Body).Section->OutSec->Addr;
+ } else if (Config->Relocatable) {
+ const uint8_t *BufLoc = RelocatedSection->Data.begin() + Rel.r_offset;
+ uint64_t Implicit = Target->getImplicitAddend(BufLoc, Type);
+ RelocatedSection->Relocations.push_back(
+ {R_ABS, Type, Rel.r_offset, Implicit, &Body});
+ }
+ }
+
// Output section VA is zero for -r, so r_offset is an offset within the
// section, but for --emit-relocs it is an virtual address.
P->r_offset = RelocatedSection->OutSec->Addr +
Modified: lld/trunk/ELF/SyntheticSections.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/SyntheticSections.cpp?rev=294816&r1=294815&r2=294816&view=diff
==============================================================================
--- lld/trunk/ELF/SyntheticSections.cpp (original)
+++ lld/trunk/ELF/SyntheticSections.cpp Fri Feb 10 19:40:49 2017
@@ -1127,8 +1127,16 @@ template <class ELFT> void SymbolTableSe
template <class ELFT>
size_t SymbolTableSection<ELFT>::getSymbolIndex(SymbolBody *Body) {
- auto I = llvm::find_if(
- Symbols, [&](const SymbolTableEntry &E) { return E.Symbol == Body; });
+ auto I = llvm::find_if(Symbols, [&](const SymbolTableEntry &E) {
+ if (E.Symbol == Body)
+ return true;
+ // This is used for -r, so we have to handle multiple section
+ // symbols being combined.
+ if (Body->Type == STT_SECTION && E.Symbol->Type == STT_SECTION)
+ return cast<DefinedRegular<ELFT>>(Body)->Section->OutSec ==
+ cast<DefinedRegular<ELFT>>(E.Symbol)->Section->OutSec;
+ return false;
+ });
if (I == Symbols.end())
return 0;
return I - Symbols.begin() + 1;
Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=294816&r1=294815&r2=294816&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Fri Feb 10 19:40:49 2017
@@ -51,6 +51,7 @@ public:
private:
void createSyntheticSections();
void copyLocalSymbols();
+ void addSectionSymbols();
void addReservedSymbols();
void addInputSec(InputSectionBase<ELFT> *S);
void createSections();
@@ -228,6 +229,9 @@ template <class ELFT> void Writer<ELFT>:
if (Config->Discard != DiscardPolicy::All)
copyLocalSymbols();
+ if (Config->copyRelocs())
+ addSectionSymbols();
+
// Now that we have a complete set of output sections. This function
// completes section contents. For example, we need to add strings
// to the string table, and add entries to .got and .plt.
@@ -446,13 +450,9 @@ template <class ELFT> void Writer<ELFT>:
template <class ELFT>
static bool shouldKeepInSymtab(InputSectionBase<ELFT> *Sec, StringRef SymName,
const SymbolBody &B) {
- if (B.isFile())
+ if (B.isFile() || B.isSection())
return false;
- // We keep sections in symtab for relocatable output and --emit-reloc.
- if (B.isSection())
- return Config->copyRelocs();
-
// If sym references a section in a discarded group, don't keep it.
if (Sec == &InputSection<ELFT>::Discarded)
return false;
@@ -518,6 +518,27 @@ template <class ELFT> void Writer<ELFT>:
}
}
+template <class ELFT> void Writer<ELFT>::addSectionSymbols() {
+ // Create one STT_SECTION symbol for each output section we might
+ // have a relocation with.
+ for (OutputSectionBase *Sec : OutputSections) {
+ InputSectionData *First = nullptr;
+ Sec->forEachInputSection([&](InputSectionData *D) {
+ if (!First)
+ First = D;
+ });
+ auto *IS = dyn_cast_or_null<InputSection<ELFT>>(First);
+ if (!IS || isa<SyntheticSection<ELFT>>(IS) || IS->Type == SHT_REL ||
+ IS->Type == SHT_RELA)
+ continue;
+ auto *B = new (BAlloc)
+ DefinedRegular<ELFT>("", /*IsLocal=*/true, /*StOther*/ 0, STT_SECTION,
+ /*Value*/ 0, /*Size*/ 0, IS, nullptr);
+
+ In<ELFT>::SymTab->addLocal(B);
+ }
+}
+
// PPC64 has a number of special SHT_PROGBITS+SHF_ALLOC+SHF_WRITE sections that
// we would like to make sure appear is a specific order to maximize their
// coverage by a single signed 16-bit offset from the TOC base pointer.
@@ -1782,8 +1803,17 @@ template <class ELFT> void Writer<ELFT>:
OutputSectionBase *EhFrameHdr =
In<ELFT>::EhFrameHdr ? In<ELFT>::EhFrameHdr->OutSec : nullptr;
+
+ // In -r or -emit-relocs mode, write the relocation sections first as in
+ // ELf_Rel targets we might find out that we need to modify the relocated
+ // section while doing it.
+ for (OutputSectionBase *Sec : OutputSections)
+ if (Sec->Type == SHT_REL || Sec->Type == SHT_RELA)
+ Sec->writeTo(Buf + Sec->Offset);
+
for (OutputSectionBase *Sec : OutputSections)
- if (Sec != Out<ELFT>::Opd && Sec != EhFrameHdr)
+ if (Sec != Out<ELFT>::Opd && Sec != EhFrameHdr && Sec->Type != SHT_REL &&
+ Sec->Type != SHT_RELA)
Sec->writeTo(Buf + Sec->Offset);
// The .eh_frame_hdr depends on .eh_frame section contents, therefore
Modified: lld/trunk/test/ELF/emit-relocs.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/emit-relocs.s?rev=294816&r1=294815&r2=294816&view=diff
==============================================================================
--- lld/trunk/test/ELF/emit-relocs.s (original)
+++ lld/trunk/test/ELF/emit-relocs.s Fri Feb 10 19:40:49 2017
@@ -15,7 +15,7 @@
# CHECK-NEXT: Section ({{.*}}) .rela.text {
# CHECK-NEXT: 0x201002 R_X86_64_32 .text 0x1
# CHECK-NEXT: 0x201007 R_X86_64_PLT32 fn 0xFFFFFFFFFFFFFFFC
-# CHECK-NEXT: 0x20100E R_X86_64_32 .text 0x1
+# CHECK-NEXT: 0x20100E R_X86_64_32 .text 0xD
# CHECK-NEXT: 0x201013 R_X86_64_PLT32 fn2 0xFFFFFFFFFFFFFFFC
# CHECK-NEXT: }
# CHECK-NEXT: ]
@@ -53,15 +53,6 @@
# CHECK-NEXT: Size: 0
# CHECK-NEXT: Binding: Local
# CHECK-NEXT: Type: Section
-# CHECK-NEXT: Other: 0
-# CHECK-NEXT: Section: .text
-# CHECK-NEXT: }
-# CHECK-NEXT: Symbol {
-# CHECK-NEXT: Name:
-# CHECK-NEXT: Value: 0x20100C
-# CHECK-NEXT: Size: 0
-# CHECK-NEXT: Binding: Local
-# CHECK-NEXT: Type: Section
# CHECK-NEXT: Other: 0
# CHECK-NEXT: Section: .text
# CHECK-NEXT: }
Modified: lld/trunk/test/ELF/mips-sto-pic-flag.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/mips-sto-pic-flag.s?rev=294816&r1=294815&r2=294816&view=diff
==============================================================================
--- lld/trunk/test/ELF/mips-sto-pic-flag.s (original)
+++ lld/trunk/test/ELF/mips-sto-pic-flag.s Fri Feb 10 19:40:49 2017
@@ -19,8 +19,8 @@
# CHECK-NEXT: Other: 0
# CHECK-NEXT: Section: .text
# CHECK-NEXT: }
-# CHECK-NEXT: Symbol {
-# CHECK-NEXT: Name: foo1a
+# CHECK: Symbol {
+# CHECK: Name: foo1a
# CHECK-NEXT: Value:
# CHECK-NEXT: Size:
# CHECK-NEXT: Binding: Global
Modified: lld/trunk/test/ELF/relocatable-bss.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/relocatable-bss.s?rev=294816&r1=294815&r2=294816&view=diff
==============================================================================
--- lld/trunk/test/ELF/relocatable-bss.s (original)
+++ lld/trunk/test/ELF/relocatable-bss.s Fri Feb 10 19:40:49 2017
@@ -20,7 +20,7 @@
# CHECK-NEXT: Version:
# CHECK-NEXT: Entry:
# CHECK-NEXT: ProgramHeaderOffset:
-# CHECK-NEXT: SectionHeaderOffset: 0xA8
+# CHECK-NEXT: SectionHeaderOffset: 0xD8
# CHECK-NEXT: Flags [
# CHECK-NEXT: ]
# CHECK-NEXT: HeaderSize:
Added: lld/trunk/test/ELF/relocatable-section-symbol.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/relocatable-section-symbol.s?rev=294816&view=auto
==============================================================================
--- lld/trunk/test/ELF/relocatable-section-symbol.s (added)
+++ lld/trunk/test/ELF/relocatable-section-symbol.s Fri Feb 10 19:40:49 2017
@@ -0,0 +1,49 @@
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+# RUN: ld.lld -r -o %t %t.o %t.o
+# RUN: llvm-readobj -r %t | FileCheck --check-prefix=RELA %s
+
+# RELA: Relocations [
+# RELA-NEXT: Section ({{.*}}) .rela.data {
+# RELA-NEXT: 0x0 R_X86_64_32 .text 0x1
+# RELA-NEXT: 0x4 R_X86_64_32 .text 0x5
+# RELA-NEXT: }
+# RELA-NEXT: ]
+
+
+# RUN: llvm-mc -filetype=obj -triple=i686-pc-linux %s -o %t.o
+# RUN: ld.lld -r -o %t %t.o %t.o
+# RUN: llvm-readobj -r -s -section-data %t | FileCheck --check-prefix=REL %s
+
+
+# REL: Section {
+# REL: Index:
+# REL: Name: .data
+# REL-NEXT: Type: SHT_PROGBITS
+# REL-NEXT: Flags [
+# REL-NEXT: SHF_ALLOC
+# REL-NEXT: SHF_WRITE
+# REL-NEXT: ]
+# REL-NEXT: Address:
+# REL-NEXT: Offset:
+# REL-NEXT: Size:
+# REL-NEXT: Link:
+# REL-NEXT: Info:
+# REL-NEXT: AddressAlignment:
+# REL-NEXT: EntrySize:
+# REL-NEXT: SectionData (
+# REL-NEXT: 0000: 01000000 05000000 |
+# REL-NEXT: )
+# REL-NEXT: }
+
+
+# REL: Relocations [
+# REL-NEXT: Section ({{.*}}) .rel.data {
+# REL-NEXT: 0x0 R_386_32 .text 0x0
+# REL-NEXT: 0x4 R_386_32 .text 0x0
+# REL-NEXT: }
+# REL-NEXT: ]
+
+
+.long 42
+.data
+.long .text + 1
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