Index: lld/ELF/Driver.cpp =================================================================== --- lld/ELF/Driver.cpp +++ lld/ELF/Driver.cpp @@ -1033,6 +1033,12 @@ for (StringRef S : Config->Undefined) Symtab->fetchIfLazy(S); + // Handle the --just-symbols option. This may add absolute symbols + // to the symbol table. + for (auto *Arg : Args.filtered(OPT_just_symbols)) + if (Optional MB = readFile(Arg->getValue())) + readJustSymbolsFile(*MB); + // If an entry symbol is in a static archive, pull out that file now // to complete the symbol table. After this, no new names except a // few linker-synthesized ones will be added to the symbol table. Index: lld/ELF/InputFiles.h =================================================================== --- lld/ELF/InputFiles.h +++ lld/ELF/InputFiles.h @@ -58,6 +58,9 @@ // Opens a given file. llvm::Optional readFile(StringRef Path); +// For --just-symbols. +template void readJustSymbolsFile(MemoryBufferRef); + // The root class of input files. class InputFile { public: Index: lld/ELF/InputFiles.cpp =================================================================== --- lld/ELF/InputFiles.cpp +++ lld/ELF/InputFiles.cpp @@ -1116,6 +1116,43 @@ } } +// This is for --just-symbols. +// +// This option allows you to link your output against other existing +// program, so that if you load both your program and the other program +// into memory, your output can use program's symbols. +// +// What we are doing here is to read defined symbols from a given ELF +// file and add them as absolute symbols. +template void elf::readJustSymbolsFile(MemoryBufferRef MB) { + typedef typename ELFT::Shdr Elf_Shdr; + typedef typename ELFT::Sym Elf_Sym; + typedef typename ELFT::SymRange Elf_Sym_Range; + + StringRef ObjName = MB.getBufferIdentifier(); + ELFFile Obj = check(ELFFile::create(MB.getBuffer())); + ArrayRef Sections = CHECK(Obj.sections(), ObjName); + + for (const Elf_Shdr &Sec : Sections) { + if (Sec.sh_type != SHT_SYMTAB) + continue; + + Elf_Sym_Range Syms = CHECK(Obj.symbols(&Sec), ObjName); + uint32_t FirstNonLocal = Sec.sh_info; + StringRef StringTable = + CHECK(Obj.getStringTableForSymtab(Sec, Sections), ObjName); + + std::vector> Ret; + for (const Elf_Sym &Sym : Syms.slice(FirstNonLocal)) + if (Sym.st_shndx != SHN_UNDEF) + Symtab->addRegular(CHECK(Sym.getName(StringTable), ObjName), + Sym.st_other, Sym.getType(), Sym.st_value, + Sym.st_size, Sym.getBinding(), nullptr, + nullptr); + return; + } +} + template void ArchiveFile::parse(); template void ArchiveFile::parse(); template void ArchiveFile::parse(); @@ -1150,3 +1187,8 @@ template void BinaryFile::parse(); template void BinaryFile::parse(); template void BinaryFile::parse(); + +template void elf::readJustSymbolsFile(MemoryBufferRef); +template void elf::readJustSymbolsFile(MemoryBufferRef); +template void elf::readJustSymbolsFile(MemoryBufferRef); +template void elf::readJustSymbolsFile(MemoryBufferRef); Index: lld/ELF/Options.td =================================================================== --- lld/ELF/Options.td +++ lld/ELF/Options.td @@ -153,6 +153,8 @@ defm init: Eq<"init">, HelpText<"Specify an initializer function">, MetaVarName<"">; +defm just_symbols: Eq<"just-symbols">, HelpText<"Just link symbols">; + defm library: Eq<"library">, HelpText<"Root name of library to use">, MetaVarName<"">; Index: lld/test/ELF/Inputs/just-symbols.s =================================================================== --- /dev/null +++ lld/test/ELF/Inputs/just-symbols.s @@ -0,0 +1,9 @@ +.globl foo, bar +foo: + ret + +.section .data +.type bar, @object +.size bar, 40 +bar: + .zero 40 Index: lld/test/ELF/just-symbols.s =================================================================== --- /dev/null +++ lld/test/ELF/just-symbols.s @@ -0,0 +1,17 @@ +# REQUIRES: x86 + +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %S/Inputs/just-symbols.s -o %t1 +# RUN: ld.lld %t1 -o %t1.exe -Ttext=0x10000 + +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t2 +# RUN: ld.lld %t2 -just-symbols=%t1.exe -o %t2.exe +# RUN: llvm-readelf -symbols %t2.exe | FileCheck %s + +# CHECK: 0000000000011000 40 OBJECT GLOBAL DEFAULT ABS bar +# CHECK: 0000000000010000 0 NOTYPE GLOBAL DEFAULT ABS foo + +.globl _start +_start: + call foo + call bar + ret