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I3S (Instruction Set Semantics Specification) Translator

The goal of this project is to simplify instruction set semantics specification generation for QEMU using high-level language (I3S).

I3S overview

I3S is C99 extension. I3S is used to avoid using low-level TCG API. More about TCG you can read in qemu/tcg/README.

I3S contain new type tcg. This type support several type specifiers: short and long. By default tcg is unsigned, but you can use signed to create signed variable. Consider the possible types:

  • tcg: target long run-time variable (equivalent TCGv);
  • long tcg: 64-bits run-time variable (equivalent TCGv_i64);
  • short tcg: 32-bits run-time variable (equivalent TCGv_i32).

A user can work with tcg variable like with other C variable with some specificity:

  • for tcg vars was added left and right rotate shifts (<<<, >>>);
  • if one of the var in expression is unsigned the result is unsigned too;
  • it is forbidden to assign tcg vars to non-tcg;
  • for tcg vars applicable rules like integer conversion rules, but the sequence of priorities is as follows: short tcg < long tcg < tcg.
  • if expression contains tcg var and C var the signedness determine by tcg var.

Implementation constraints:

  • Doesn't use tcg var in return expression.
  • Does't support tcg var pointer.
  • Global tcg var must be only extern.
  • Loop for is tcg dependent if the condition is tcg dependent.

ATTENSION: Try to avoid declare variadles with the same name, because the compound will be converted to linear code without compound for tcg-depended if/loops. The tool only ensure that variable in tcg-depended if/loops will be renamed if its name has been encountered before. Renaming is done by adding a suffix to the name. A message with a new name of vars and line number in src file will be displayed in console after renaming. Also renaming don't work for delaration in init in 'For' loop.

To become familiar with all restrictions you need to read TODO.

TODO:

  • Array:

    • support tcg index (by automatic helpers generation);
    • fixup pointer handling: if a[n][k] has tcg type ==> a[n] has tcg type too (a[n] shoud be a pointer).

  • Analysis functions body and arguments for specific tcg expressions.

  • Support tcg fields in Struct and Union.

  • Warning when tcg var dependent if/loops contains C vars.

  • Tracs basic block only for tcg var.

  • Support special tcg conditional Always/Never (True/False).

  • Support ternary operator.

  • Support if/loops without compounds that contains tcg-expression, because tcg expression can deploy to several C expression.

  • Integrate gen_set_label sequences in one.

  • Check matching of automatically generated var names with vars in specification.

  • Take into account the typedef tcg type.

  • Reuse tcg var after free: doesn't declare new var, just make tcg_temp_new.

Getting started

The tool is written in Python. Both 2.7.3+ and 3.3+ versions are supported.

I3S test shoud be run using 3.3+ Python.

How to run

python i3s_to_c.py --in-file i3s_in.c --out-file tcg_out.c

If you want to view AST you can use --out-astfile ast.txt.

Use --debug or -d to run I3S in debug mode. In this mode tool automatically add comments with the original I3S language constructs to generated file.

Run test

python run_test.py

Test locate in \test\i3s.

The essence of the test is to compare the generated from the i3s.c new code with code that was generated before tools modification.

The reference standards is stored in i3s_reference_standards.c.

You can update i3s_reference_standards.c using

python update_reference_standarts.py