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Add support for emitting the symbol table (and its string table) of the

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module to the ELF file.  Test it by adding support for emitting common
symbols.  This allows us to compile this:

%X = weak global int 0
%Y = weak global int 0
%Z = weak global int 0

to an elf file that 'readelf's this:

Symbol table '.symtab' contains 4 entries:
   Num:    Value  Size Type    Bind   Vis      Ndx Name
     0: 00000000     0 NOTYPE  LOCAL  DEFAULT  UND
     1: 00000004     4 OBJECT  GLOBAL DEFAULT  COM X
     2: 00000004     4 OBJECT  GLOBAL DEFAULT  COM Y
     3: 00000004     4 OBJECT  GLOBAL DEFAULT  COM Z


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@22343 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2005-07-07 07:02:20 +00:00
parent e578ab938b
commit 80ed8faaea
1 changed files with 140 additions and 53 deletions
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193
lib/CodeGen/ELFWriter.cpp
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@ -11,17 +11,18 @@
// the ELF file in the following order:
//
// #1. ELF Header
// #2. '.data' section
// #3. '.bss' section
// #2. '.text' section
// #3. '.data' section
// #4. '.bss' section (conceptual position in file)
// ...
// #X. '.shstrtab' section
// #Y. Section Table
//
// The entries in the section table are laid out as:
// #0. Null entry [required]
// #1. ".data" entry - global variables with initializers. [ if needed ]
// #2. ".bss" entry - global variables without initializers. [ if needed ]
// #3. ".text" entry - the program code
// #1. ".text" entry - the program code
// #2. ".data" entry - global variables with initializers. [ if needed ]
// #3. ".bss" entry - global variables without initializers. [ if needed ]
// ...
// #N. ".shstrtab" entry - String table for the section names.
@ -83,62 +84,50 @@ bool ELFWriter::doInitialization(Module &M) {
// Add the null section.
SectionList.push_back(ELFSection());
// Okay, the ELF header has been completed, emit the .data section next.
ELFSection DataSection(".data", OutputBuffer.size());
for (Module::global_iterator I = M.global_begin(), E = M.global_end();
I != E; ++I)
EmitDATASectionGlobal(I);
// Start up the symbol table. The first entry in the symtab is the null
// entry.
SymbolTable.push_back(ELFSym(0));
// If the .data section is nonempty, add it to our list.
if ((DataSection.Size = OutputBuffer.size()-DataSection.Offset)) {
DataSection.Align = 4; // FIXME: Compute!
SectionList.push_back(DataSection);
}
// Okay, emit the .bss section next.
ELFSection BSSSection(".bss", OutputBuffer.size());
for (Module::global_iterator I = M.global_begin(), E = M.global_end();
I != E; ++I)
EmitBSSSectionGlobal(I);
// If the .bss section is nonempty, add it to our list.
if ((BSSSection.Size = OutputBuffer.size()-BSSSection.Offset)) {
BSSSection.Align = 4; // FIXME: Compute!
SectionList.push_back(BSSSection);
}
// FIXME: Should start the .text section.
return false;
}
// isCOMM - A global variable should be emitted to the common area if it is zero
// initialized and has linkage that permits it to be merged with other globals.
static bool isCOMM(GlobalVariable *GV) {
return GV->getInitializer()->isNullValue() &&
(GV->hasLinkOnceLinkage() || GV->hasInternalLinkage() ||
GV->hasWeakLinkage());
}
void ELFWriter::EmitGlobal(GlobalVariable *GV, ELFSection &DataSection,
ELFSection &BSSSection) {
// If this is an external global, emit it...
assert(GV->hasInitializer() && "FIXME: unimp");
// If this global has a zero initializer, it is part of the .bss or common
// section.
if (GV->getInitializer()->isNullValue()) {
// If this global is part of the common block, add it now. Variables are
// part of the common block if they are zero initialized and allowed to be
// merged with other symbols.
if (GV->hasLinkOnceLinkage() || GV->hasWeakLinkage()) {
ELFSym CommonSym(GV);
// Value for common symbols is the alignment required.
const Type *GVType = (const Type*)GV->getType();
CommonSym.Value = TM.getTargetData().getTypeAlignment(GVType);
CommonSym.Size = TM.getTargetData().getTypeSize(GVType);
CommonSym.SetBind(ELFSym::STB_GLOBAL);
CommonSym.SetType(ELFSym::STT_OBJECT);
// TODO SOMEDAY: add ELF visibility.
CommonSym.SectionIdx = ELFSection::SHN_COMMON;
SymbolTable.push_back(CommonSym);
return;
}
// EmitDATASectionGlobal - Emit a global variable to the .data section if it
// belongs there.
void ELFWriter::EmitDATASectionGlobal(GlobalVariable *GV) {
if (!GV->hasInitializer()) return;
// FIXME: Implement the .bss section.
return;
}
// Do not emit a symbol here if it should be emitted to the common area.
if (isCOMM(GV)) return;
// FIXME: handle .rodata
//assert(!GV->isConstant() && "unimp");
EmitGlobal(GV);
}
void ELFWriter::EmitBSSSectionGlobal(GlobalVariable *GV) {
if (!GV->hasInitializer()) return;
// FIXME: We don't support BSS yet!
return;
EmitGlobal(GV);
}
void ELFWriter::EmitGlobal(GlobalVariable *GV) {
// FIXME: handle .data
//assert(0 && "unimp");
}
@ -149,6 +138,37 @@ bool ELFWriter::runOnMachineFunction(MachineFunction &MF) {
/// doFinalization - Now that the module has been completely processed, emit
/// the ELF file to 'O'.
bool ELFWriter::doFinalization(Module &M) {
// Okay, the .text section has now been finalized.
// FIXME: finalize the .text section.
// Okay, the ELF header and .text sections have been completed, build the
// .data, .bss, and "common" sections next.
ELFSection DataSection(".data", OutputBuffer.size());
ELFSection BSSSection (".bss");
for (Module::global_iterator I = M.global_begin(), E = M.global_end();
I != E; ++I)
EmitGlobal(I, DataSection, BSSSection);
// If the .data section is nonempty, add it to our list.
if (DataSection.Size) {
DataSection.Align = 4; // FIXME: Compute!
// FIXME: Set the right flags and stuff.
SectionList.push_back(DataSection);
}
// If the .bss section is nonempty, add it to our list.
if (BSSSection.Size) {
BSSSection.Offset = OutputBuffer.size();
BSSSection.Align = 4; // FIXME: Compute!
// FIXME: Set the right flags and stuff.
SectionList.push_back(BSSSection);
}
// Emit the symbol table now, if non-empty.
EmitSymbolTable();
// FIXME: Emit the relocations now.
// Emit the string table for the sections in the ELF file we have.
EmitSectionTableStringTable();
@ -163,13 +183,80 @@ bool ELFWriter::doFinalization(Module &M) {
return false;
}
/// EmitSymbolTable - If the current symbol table is non-empty, emit the string
/// table for it and then the symbol table itself.
void ELFWriter::EmitSymbolTable() {
if (SymbolTable.size() == 1) return; // Only the null entry.
// FIXME: compact all local symbols to the start of the symtab.
unsigned FirstNonLocalSymbol = 1;
SectionList.push_back(ELFSection(".strtab", OutputBuffer.size()));
ELFSection &StrTab = SectionList.back();
StrTab.Type = ELFSection::SHT_STRTAB;
StrTab.Align = 1;
// Set the zero'th symbol to a null byte, as required.
outbyte(0);
SymbolTable[0].NameIdx = 0;
unsigned Index = 1;
for (unsigned i = 1, e = SymbolTable.size(); i != e; ++i) {
// FIXME: USE A MANGLER!!
const std::string &Name = SymbolTable[i].GV->getName();
if (Name.empty()) {
SymbolTable[i].NameIdx = 0;
} else {
SymbolTable[i].NameIdx = Index;
// Add the name to the output buffer, including the null terminator.
OutputBuffer.insert(OutputBuffer.end(), Name.begin(), Name.end());
// Add a null terminator.
OutputBuffer.push_back(0);
// Keep track of the number of bytes emitted to this section.
Index += Name.size()+1;
}
}
StrTab.Size = OutputBuffer.size()-StrTab.Offset;
// Now that we have emitted the string table and know the offset into the
// string table of each symbol, emit the symbol table itself.
assert(!is64Bit && "Should this be 8 byte aligned for 64-bit?"
" (check .Align below also)");
align(4);
SectionList.push_back(ELFSection(".symtab", OutputBuffer.size()));
ELFSection &SymTab = SectionList.back();
SymTab.Type = ELFSection::SHT_SYMTAB;
SymTab.Align = 4; // FIXME: check for ELF64
SymTab.Link = SectionList.size()-2; // Section Index of .strtab.
SymTab.Info = FirstNonLocalSymbol; // First non-STB_LOCAL symbol.
SymTab.EntSize = 16; // Size of each symtab entry. FIXME: wrong for ELF64
assert(!is64Bit && "check this!");
for (unsigned i = 0, e = SymbolTable.size(); i != e; ++i) {
ELFSym &Sym = SymbolTable[i];
outword(Sym.NameIdx);
outaddr(Sym.Value);
outword(Sym.Size);
outbyte(Sym.Info);
outbyte(Sym.Other);
outhalf(Sym.SectionIdx);
}
SymTab.Size = OutputBuffer.size()-SymTab.Offset;
}
/// EmitSectionTableStringTable - This method adds and emits a section for the
/// ELF Section Table string table: the string table that holds all of the
/// section names.
void ELFWriter::EmitSectionTableStringTable() {
// First step: add the section for the string table to the list of sections:
SectionList.push_back(ELFSection(".shstrtab", OutputBuffer.size()));
SectionList.back().Type = 3; // SHT_STRTAB
SectionList.back().Type = ELFSection::SHT_STRTAB;
// Now that we know which section number is the .shstrtab section, update the
// e_shstrndx entry in the ELF header.