[llvm-dev] Have LLD load a file through memory (original) (raw)

Frank Winter via llvm-dev llvm-dev at lists.llvm.org
Thu Aug 12 14:21:47 PDT 2021

Hi.

I'm trying to use LLD to get it's input file from a string in memory instead of a file.

My use case is a JIT compiler (IR --> AMD GCN ISA) where calling the linker to make it a loadable object via system() is hitting a bug (somewhere in the system).

Here's what I do:

  1. With the AMDGPU backend I write the output to a string
  2. I sneak in this string into LLD via an added access function.
  3. Since LLD invocation is only used in this form: ld.lld -shared k.o -o k.so I modified 'elf::readFile' to

std::string tmp = qdp_jit_get_object(); // this retrieves the sneaky string

llvm::outs() << "size = " << tmp.size() << "\n";

std::unique_ptr mb = MemoryBuffer::getMemBuffer( StringRef( tmp.c_str() , tmp.length() ) );

MemoryBufferRef mbref = mb->getMemBufferRef();

return mbref;

When I then call LLD via lld:🧝:link, I get

size = 2192 ld: error: :1: unknown directive:

A�E�A�E�@���?V@���?V�3��������}j<������� �J�0�ւ���j� ^

This is how the string containing the object was created:

string str_obj; llvm::raw_string_ostream rss(str_obj); llvm::buffer_ostream bos(rss);

if (TargetMachine->addPassesToEmitFile(CodeGenPasses, bos, nullptr, llvm::CodeGenFileType::CGFT_ObjectFile ))

CodeGenPasses.run(*Mod);

Is there anything wrong how I turn the string into a MemoryBuffer so that the link fails?

Thanks, Frank

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