I get a crash when I try to link multiple modules registered in their
individual contexts.
Documentation for Linker::LinkModules doesn't mention anything about
contexts, and the first link succeeds. But the second link crashes.
Is this not the right way to merge such modules? If not, then what is
the right way?
In any case, documentation for Linker::LinkModules should say if
contexts are or aren't expected to be the same.
Yuri
---testcase---
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/Linker/Linker.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/IR/DiagnosticPrinter.h"
#include <string>
#include <iostream>
using namespace llvm;
using namespace std;
int main() {
// vars
string Message;
raw_string_ostream Stream(Message);
DiagnosticPrinterRawOStream DP(Stream);
LLVMBool Result;
// create blank modules and contexts
LLVMContext *ctx1 = new LLVMContext;
Module* module1 = new Module("module1", *ctx1);
LLVMContext *ctx2 = new LLVMContext;
Module* module2 = new Module("module2", *ctx2);
LLVMContext *ctx3 = new LLVMContext;
Module* module3 = new Module("module3", *ctx3);
// fill modules
llvm::Function::Create(llvm::FunctionType::get(Type::getInt32Ty(*ctx1),
false), llvm::Function::ExternalLinkage, "f1", module1);
llvm::Function::Create(llvm::FunctionType::get(Type::getInt32Ty(*ctx2),
false), llvm::Function::ExternalLinkage, "f2", module2);
llvm::Function::Create(llvm::FunctionType::get(Type::getInt32Ty(*ctx3),
false), llvm::Function::ExternalLinkage, "f3", module3);
// merge f1 <- f2
Result = Linker::LinkModules(module1, module2, [&](const
DiagnosticInfo &DI) {DI.print(DP);});
cout << "merge result=" << Result << endl;
delete ctx2;
cout << "--done merge #1--" << endl;
// merge f3 <- f1
Result = Linker::LinkModules(module3, module1, [&](const
DiagnosticInfo &DI) {DI.print(DP);});
cout << "merge result=" << Result << endl;
delete ctx1;
cout << "--done merge #2--" << endl;
return 0;
}
---output---
merge result=0
--done merge #1--
Bus error
rev.237344
I'm pretty sure module linking is expected to occur in the same LLVM context. IIRC Duncan had some proposal for how ld64 could do something clever with multiple contexts, but I've totally forgotten what it was. On Fri, May 29, 2015 at 5:18 PM, Yuri <yuri at rawbw.com> wrote:> I get a crash when I try to link multiple modules registered in their > individual contexts. > Documentation for Linker::LinkModules doesn't mention anything about > contexts, and the first link succeeds. But the second link crashes. > > Is this not the right way to merge such modules? If not, then what is the > right way? > > In any case, documentation for Linker::LinkModules should say if contexts > are or aren't expected to be the same. > > Yuri > > > ---testcase--- > #include "llvm/IR/LLVMContext.h" > #include "llvm/IR/Module.h" > #include "llvm/Linker/Linker.h" > #include "llvm/Support/raw_ostream.h" > #include "llvm/IR/DiagnosticPrinter.h" > #include <string> > #include <iostream> > > using namespace llvm; > using namespace std; > > int main() { > // vars > string Message; > raw_string_ostream Stream(Message); > DiagnosticPrinterRawOStream DP(Stream); > LLVMBool Result; > // create blank modules and contexts > LLVMContext *ctx1 = new LLVMContext; > Module* module1 = new Module("module1", *ctx1); > LLVMContext *ctx2 = new LLVMContext; > Module* module2 = new Module("module2", *ctx2); > LLVMContext *ctx3 = new LLVMContext; > Module* module3 = new Module("module3", *ctx3); > // fill modules > llvm::Function::Create(llvm::FunctionType::get(Type::getInt32Ty(*ctx1), > false), llvm::Function::ExternalLinkage, "f1", module1); > llvm::Function::Create(llvm::FunctionType::get(Type::getInt32Ty(*ctx2), > false), llvm::Function::ExternalLinkage, "f2", module2); > llvm::Function::Create(llvm::FunctionType::get(Type::getInt32Ty(*ctx3), > false), llvm::Function::ExternalLinkage, "f3", module3); > > // merge f1 <- f2 > Result = Linker::LinkModules(module1, module2, [&](const DiagnosticInfo > &DI) {DI.print(DP);}); > cout << "merge result=" << Result << endl; > delete ctx2; > cout << "--done merge #1--" << endl; > > // merge f3 <- f1 > Result = Linker::LinkModules(module3, module1, [&](const DiagnosticInfo > &DI) {DI.print(DP);}); > cout << "merge result=" << Result << endl; > delete ctx1; > cout << "--done merge #2--" << endl; > > return 0; > } > > ---output--- > merge result=0 > --done merge #1-- > Bus error > > rev.237344 > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150601/dbb247c6/attachment.html>
Duncan P. N. Exon Smith
2015-Jun-01 18:43 UTC
[LLVMdev] Linking modules across contexts crashes
> On 2015-Jun-01, at 11:06, Reid Kleckner <rnk at google.com> wrote: > > I'm pretty sure module linking is expected to occur in the same LLVM context.Correct.> IIRC Duncan had some proposal for how ld64 could do something clever with multiple contexts, but I've totally forgotten what it was.This was for LTO (probably unrelated to Yuri's scenario?). 1. Lazy-load each module in its own context, parse its symbols (without actually loading functions, metadata, etc.), and destroy the module and context. 2. Decide which modules we should link (based on symbol parsing). 3. Load all the chosen modules into a single context and link them together. lib/LTO has a bunch of the pieces for this, but I got the idea from Rafael's work on tools/gold-plugin/gold-plugin.cpp. It might be easier to look at there.> On Fri, May 29, 2015 at 5:18 PM, Yuri <yuri at rawbw.com> wrote: > I get a crash when I try to link multiple modules registered in their individual contexts. > Documentation for Linker::LinkModules doesn't mention anything about contexts, and the first link succeeds. But the second link crashes.The problem is that a fair number of things referenced by a Module are owned by its LLVMContext (types, constants, metadata, and some other things).> Is this not the right way to merge such modules? If not, then what is the right way?You can round-trip to bitcode, reading the module into the destination context. The following pseudo-code gives the idea: bool linkModuleFromDifferentContext(Module &D, const Module &S) { SmallVector<char, 256> Buffer; writeBitcodeToBuffer(S, Buffer); std::unique_ptr<Module> M = readBitcodeFromBuffer(D.getContext()); return Linker::LinkModules(&D, M.get()); }> In any case, documentation for Linker::LinkModules should say if contexts are or aren't expected to be the same.Good idea; patch welcome.> > Yuri > > > ---testcase--- > #include "llvm/IR/LLVMContext.h" > #include "llvm/IR/Module.h" > #include "llvm/Linker/Linker.h" > #include "llvm/Support/raw_ostream.h" > #include "llvm/IR/DiagnosticPrinter.h" > #include <string> > #include <iostream> > > using namespace llvm; > using namespace std; > > int main() { > // vars > string Message; > raw_string_ostream Stream(Message); > DiagnosticPrinterRawOStream DP(Stream); > LLVMBool Result; > // create blank modules and contexts > LLVMContext *ctx1 = new LLVMContext; > Module* module1 = new Module("module1", *ctx1); > LLVMContext *ctx2 = new LLVMContext; > Module* module2 = new Module("module2", *ctx2); > LLVMContext *ctx3 = new LLVMContext; > Module* module3 = new Module("module3", *ctx3); > // fill modules > llvm::Function::Create(llvm::FunctionType::get(Type::getInt32Ty(*ctx1), false), llvm::Function::ExternalLinkage, "f1", module1); > llvm::Function::Create(llvm::FunctionType::get(Type::getInt32Ty(*ctx2), false), llvm::Function::ExternalLinkage, "f2", module2); > llvm::Function::Create(llvm::FunctionType::get(Type::getInt32Ty(*ctx3), false), llvm::Function::ExternalLinkage, "f3", module3); > > // merge f1 <- f2 > Result = Linker::LinkModules(module1, module2, [&](const DiagnosticInfo &DI) {DI.print(DP);}); > cout << "merge result=" << Result << endl; > delete ctx2; > cout << "--done merge #1--" << endl; > > // merge f3 <- f1 > Result = Linker::LinkModules(module3, module1, [&](const DiagnosticInfo &DI) {DI.print(DP);}); > cout << "merge result=" << Result << endl; > delete ctx1; > cout << "--done merge #2--" << endl; > > return 0; > } > > ---output--- > merge result=0 > --done merge #1-- > Bus error > > rev.237344 > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev >