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[ELF] Allow references to reserved symbols in linker scripts 

This requires collectign all symbols referenced in the linker script
and adding them to symbol table as undefined symbol.

Differential Revision: https://reviews.llvm.org/D31147

llvm-svn: 298577
This commit is contained in:
Petr Hosek 2017-03-23 03:52:34 +00:00
parent 968381ef22
commit 30f16b2339
4 changed files with 31 additions and 4 deletions
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5
lld/ELF/Driver.cpp
View File

@ -921,6 +921,11 @@ template <class ELFT> void LinkerDriver::link(opt::InputArgList &Args) {
if (ErrorCount)
return;
// Some symbols (such as __ehdr_start) are defined lazily only when there
// are undefined symbols for them, so we add these to trigger that logic.
for (StringRef Sym : Script->Opt.UndefinedSymbols)
Symtab.addUndefined(Sym);
for (auto *Arg : Args.filtered(OPT_wrap))
Symtab.wrap(Arg->getValue());

11
lld/ELF/LinkerScript.cpp
View File

@ -999,8 +999,8 @@ ExprValue LinkerScript::getSymbolValue(const Twine &Loc, StringRef S) {
if (SymbolBody *B = findSymbol(S)) {
if (auto *D = dyn_cast<DefinedRegular>(B))
return {D->Section, D->Value};
auto *C = cast<DefinedCommon>(B);
return {InX::Common, C->Offset};
if (auto *C = dyn_cast<DefinedCommon>(B))
return {InX::Common, C->Offset};
}
error(Loc + ": symbol not found: " + S);
return 0;
@ -1867,8 +1867,11 @@ Expr ScriptParser::readPrimary() {
return [=] { return V; };
// Tok is a symbol name.
if (Tok != "." && !isValidCIdentifier(Tok))
setError("malformed number: " + Tok);
if (Tok != ".") {
if (!isValidCIdentifier(Tok))
setError("malformed number: " + Tok);
Script->Opt.UndefinedSymbols.push_back(Tok);
}
return [=] { return Script->getSymbolValue(Location, Tok); };
}

3
lld/ELF/LinkerScript.h
View File

@ -217,6 +217,9 @@ struct ScriptConfiguration {
// A map from memory region name to a memory region descriptor.
llvm::DenseMap<llvm::StringRef, MemoryRegion> MemoryRegions;
// A list of undefined symbols referenced by the script.
std::vector<llvm::StringRef> UndefinedSymbols;
};
class LinkerScript {

16
lld/test/ELF/linkerscript/symbol-reserved.s Normal file
View File

@ -0,0 +1,16 @@
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
# RUN: echo "PROVIDE_HIDDEN(newsym = __ehdr_start + 5);" > %t.script
# RUN: ld.lld -o %t1 %t.script %t
# RUN: llvm-objdump -t %t1 | FileCheck %s
# CHECK: 0000000000200005 .text 00000000 .hidden newsym
# RUN: ld.lld -o %t1.so %t.script %t -shared
# RUN: llvm-objdump -t %t1.so | FileCheck --check-prefix=SHARED %s
# SHARED: 0000000000000005 .dynsym 00000000 .hidden newsym
.global _start
_start:
lea newsym(%rip),%rax