About

This directory contains the services required to execute both nexes and pexes.

Using

For information about how to build and use nexes and pexes from within Mojo, refer to the mojo/nacl directory.

Non-SFI Nexe Content Handler

The nexe content handler is simple. It:

1. Acquires the desired nexe and dumps it into a temporary file,
2. Accesses the MojoHandle connecting the content handler to the shell, and
3. Launches the Non-SFI nexe.

Non-SFI Pexe Content Handler

The pexe content handler is slightly more complex. Although it is similar in structure to the Non-SFI nexe content handler, it has an additional step between item 1 and 2: convert the incoming pexe into a nexe.

This pexe to nexe translation requires two steps: compilation and linking. For each of these steps, a helper service is launched. These helper services are actually executed as nexes -- pnacl_llc.nexe and ld.nexe. The translation done by these nexes is executed as part of a callback to IRT functions, nacl_irt_private_pnacl_translator_compile, and nacl_irt_private_pnacl_translator_link. This makes communication between the content handler and these helper nexes more complicated.

For the full picture of the compilation process:

• PexeContentHandler
  • Create a message pipe, which has a parent and child handle
  • Call PexeCompilerStart, passing in the child end of the message pipe. This contacts a new service which is responsible for launching pnacl_llc.nexe.
• PexeCompiler (new process)
  • Launch the pnacl_llc nexe using the child end of the pipe received from the PexeContentHandler
  • The pnacl_llc nexe uses the IRT to make a call to ServeTranslateRequest (defined in mojo/nacl/nonsfi/irt_pnacl_translator_compile.cc). This creates the PexeCompiler service, which is ready to handle a single request. It is bound to the child end of the pipe.
• Meanwhile, back in the PexeContentHandler:
  • Bind the parent end of the pipe to a PexeCompiler service. Now, PexeCompile can be called with inputs defined by a mojom interface, and outputs can be received via callback
  • Call PexeCompile, passing in the name of the pexe, and receiving the object files created by compilation
• Meanwhile, back in the pnacl_llc nexe:
  • Actually do the requested compilation, and pass back the newly created object files

The linking process works similarly, but utilizes a different interface which lets it receive object files and return a linked nexe.

Once both the compilation and linking steps have been completed, the PexeContentHandler is able to launch the requested nexe.

TODO

• Turn the NexeContentHandler, PexeContentHandler, PexeCompiler, and PexeLinker services into “anti-singletons”. When each service is requested, a unique process must be created.
• Use subzero (a NaCl project to improve translation speed) for pexe translation.
• Enable caching of translated pexes.