Use the ability to pwrite to simplify the ELF writer.
Now we don't have to do 2 synchronized passes to compute offsets and then
write the file.
This also includes a fix for the corner case of seeking in /dev/null. It
is not an error, but on some systems (Linux) the returned offset is
always 0. An error is signaled by returning -1. This is checked by
the existing tests now that "clang -o /dev/null ..." seeks.
llvm-svn: 234952
diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index 2b8b8ba..583f2fd 100644
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -92,14 +92,11 @@
static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc);
static bool IsELFMetaDataSection(const MCSectionData &SD);
static uint64_t DataSectionSize(const MCSectionData &SD);
- static uint64_t GetSectionFileSize(const MCAsmLayout &Layout,
- const MCSectionData &SD);
static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout,
const MCSectionData &SD);
- void WriteDataSectionData(MCAssembler &Asm,
- const MCAsmLayout &Layout,
- const MCSectionELF &Section);
+ void writeDataSectionData(MCAssembler &Asm, const MCAsmLayout &Layout,
+ const MCSectionData &SD);
/// Helper struct for containing some precomputed information on symbols.
struct ELFSymbolData {
@@ -201,7 +198,6 @@
}
void WriteHeader(const MCAssembler &Asm,
- uint64_t SectionHeaderOffset,
unsigned NumberOfSections);
void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
@@ -409,7 +405,6 @@
// Emit the ELF header.
void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
- uint64_t SectionHeaderOffset,
unsigned NumberOfSections) {
// ELF Header
// ----------
@@ -443,7 +438,7 @@
Write32(ELF::EV_CURRENT); // e_version
WriteWord(0); // e_entry, no entry point in .o file
WriteWord(0); // e_phoff, no program header for .o
- WriteWord(SectionHeaderOffset); // e_shoff = sec hdr table off in bytes
+ WriteWord(0); // e_shoff = sec hdr table off in bytes
// e_flags = whatever the target wants
Write32(Asm.getELFHeaderEFlags());
@@ -1532,13 +1527,6 @@
return Ret;
}
-uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout,
- const MCSectionData &SD) {
- if (IsELFMetaDataSection(SD))
- return DataSectionSize(SD);
- return Layout.getSectionFileSize(&SD);
-}
-
uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
const MCSectionData &SD) {
if (IsELFMetaDataSection(SD))
@@ -1546,14 +1534,9 @@
return Layout.getSectionAddressSize(&SD);
}
-void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm,
+void ELFObjectWriter::writeDataSectionData(MCAssembler &Asm,
const MCAsmLayout &Layout,
- const MCSectionELF &Section) {
- const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
-
- uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
- WriteZeros(Padding);
-
+ const MCSectionData &SD) {
if (IsELFMetaDataSection(SD)) {
for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
++i) {
@@ -1655,45 +1638,49 @@
const_cast<MCAsmLayout&>(Layout),
SectionIndexMap);
- uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
- uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
- sizeof(ELF::Elf32_Ehdr);
- uint64_t FileOff = HeaderSize;
-
std::vector<const MCSectionELF*> Sections;
ComputeSectionOrder(Asm, Sections);
unsigned NumSections = Sections.size();
SectionOffsetMapTy SectionOffsetMap;
- for (unsigned i = 0; i < NumSections; ++i) {
-
- const MCSectionELF &Section = *Sections[i];
- const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
-
- FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
-
- // Remember the offset into the file for this section.
- SectionOffsetMap[&Section] = FileOff;
-
- // Get the size of the section in the output file (including padding).
- FileOff += GetSectionFileSize(Layout, SD);
- }
-
- FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
-
- const unsigned SectionHeaderOffset = FileOff;
// Write out the ELF header ...
- WriteHeader(Asm, SectionHeaderOffset, NumSections + 1);
+ WriteHeader(Asm, NumSections + 1);
// ... then the sections ...
- for (unsigned i = 0; i < NumSections; ++i)
- WriteDataSectionData(Asm, Layout, *Sections[i]);
+ for (unsigned i = 0; i < NumSections; ++i) {
+ const MCSectionELF &Section = *Sections[i];
+ const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
+ uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
+ WriteZeros(Padding);
+ // Remember the offset into the file for this section.
+ SectionOffsetMap[&Section] = OS.tell();
+
+ writeDataSectionData(Asm, Layout, SD);
+ }
+
+ uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
WriteZeros(Padding);
+ const unsigned SectionHeaderOffset = OS.tell();
+
// ... then the section header table ...
writeSectionHeader(Asm, GroupMap, Layout, SectionIndexMap, SectionOffsetMap);
+
+ if (is64Bit()) {
+ uint64_t Val = SectionHeaderOffset;
+ if (sys::IsLittleEndianHost != IsLittleEndian)
+ sys::swapByteOrder(Val);
+ OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
+ offsetof(ELF::Elf64_Ehdr, e_shoff));
+ } else {
+ uint32_t Val = SectionHeaderOffset;
+ if (sys::IsLittleEndianHost != IsLittleEndian)
+ sys::swapByteOrder(Val);
+ OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
+ offsetof(ELF::Elf32_Ehdr, e_shoff));
+ }
}
bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(