Add an IRT interface for subzero/compiler to serve_translate_requests.

src/untrusted/irt/irt_dev.h

Index: src/untrusted/irt/irt_dev.h
diff --git a/src/untrusted/irt/irt_dev.h b/src/untrusted/irt/irt_dev.h
index 8a6f78300f4cb35b3375726457f7aeb3c7dbc222..0aaf2063ea7a7a33d313acf167dffc755e8b594a 100644
--- a/src/untrusted/irt/irt_dev.h
+++ b/src/untrusted/irt/irt_dev.h
@@ -138,6 +138,48 @@ struct nacl_irt_private_pnacl_translator_link {
                                          int obj_file_fd_count));
 };
 
+/*
+ * This is an internal interface, for use by PNaCl's subzero translator for

[Jim Stichnoth, 2015/03/23 18:13:40]

Sorry for the pedantry - can we capitalize Subzero in descriptive text? :)

Or, use the pnacl-sz tool name?

[jvoung (off chromium), 2015/03/23 21:18:55]

Alright, well if we are going with a shared pnacl-sz/pnacl-llc
interface I'll remove all mentions of Subzero, subzero and SubZero.

+ * communicating with the browser.
+ *
+ * serve_translate_request(funcs) loops waiting for sequences of requests
+ * via IPC, and then calls the appropriate callback to handle the IPC,
+ * on the same thread.
+ *
+ * (*) init_callback is used to initialze the translation process

[Jim Stichnoth, 2015/03/23 18:13:40]

initialize

[jvoung (off chromium), 2015/03/23 21:18:55]

Done.

+ *     with configuration info:
+ *     |num_threads| is the number of recommended *translate* threads
+ *     to use (there may be other worker threads).

[Jim Stichnoth, 2015/03/23 18:13:40]

Mention that num_threads=0 means completely sequential?

[jvoung (off chromium), 2015/03/23 21:18:55]

Hmm, alright added that conditional on pnacl-sz. In practice, the browser won't
really pick 0 unless you make a custom build. On the other hand, it could be
easy to pick 0 with the commandline pnacl-translate tool.

+ *     |obj_file_fd| is the FD for writing an output object file.
+ *     |cmd_flags| is \0 delimited set of command-line flags.
+ *     |cmd_flags_len| is the length of the |cmd_flags| array.
+ * (*) data_callback is invoked to stream additional bitcode data
+ *     to the translator.
+ * (*) end_callback is invoked to signal the end of the data stream.
+ *     This must block until translation is actually complete and
+ *     the translator process can be terminated.
+ *
+ * All callbacks return zero on success or a non-zero value on error.
+ * TODO(jvoung): Add error output.
+ */
+struct PNaClSubzeroFunctions {

[Mark Seaborn, 2015/03/23 18:09:38]

Nit: Use lower_case_with_underscores, following the style of the IRT interfaces

[jvoung (off chromium), 2015/03/23 21:18:55]

Done.

+  int (*init_callback)(uint32_t num_threads,
+                       int obj_file_fd,

[Mark Seaborn, 2015/03/23 18:15:56]

So I guess this is specific to Subzero?  llc would want multiple FDs here.  (As
an aside, how come Subzero doesn't?)

Can you make this applicable to llc too, please?  Otherwise we'd need separate
interfaces for llc and Subzero, or a cross-repo change to change this interface.

[Jim Stichnoth, 2015/03/23 18:21:16]

Subzero doesn't need to resort to module splitting for multithreaded
translation:
 - A parser thread creates initial CFGs and adds them to a work queue
 - Multiple translation threads draw from the work queue and insert assembler
buffers into an emit queue
 - An emitter thread draws from the emit queue and writes to the ELF output
file, taking care to emit in the same (deterministic) order that things were
parsed.

[jvoung (off chromium), 2015/03/23 21:18:55]

Right.

Alright, I guess Petr is close enough to using the IRT for pnacl-llc, and they
are similar enough for now that we could share this layer. The tools will just
use what they need.

On the other hand, the browser will need to be aware if it's linking for
pnacl-llc or pnacl-sz. It turns out that the linker won't "tolerate empty
files".

If we later want to do something special for subzero like a combined
compile+link, we could add a new interface version with a new method.

Sharing would also argue for having separate methods for anything specific to
subzero. E.g., not return internal UMA info in the "end_callback" but have a
separate method.

+                       const char *cmd_flags, size_t cmd_flags_len);
+
+  int (*data_callback)(unsigned char *data, size_t num_bytes);
+  // TODO(jvoung): UMA out-arg vector, or have a separate method
+  // for that?
+  int (*end_callback)(void);
+};
+
+#define NACL_IRT_PRIVATE_PNACL_TRANSLATOR_SUBZERO_v0_1 \
+  "nacl-irt-private-pnacl-trnalsator-subzero-0.1"

[Mark Seaborn, 2015/03/23 18:09:38]

"translator" typo

Can you avoid naming this after Subzero, please?  Is there any reason this
wouldn't be usable with llc?

e.g. Name this as "compile" rather than "subzero".

[Jim Stichnoth, 2015/03/23 18:13:40]

translator

[jvoung (off chromium), 2015/03/23 21:18:55]

Done.

+struct nacl_irt_private_pnacl_translator_subzero {
+  void (*serve_translate_request)(const struct PNaClSubzeroFunctions *funcs);
+  void (*log_fatal)(const char *message);
+};
+
 #if defined(__cplusplus)
 }
 #endif