SimpleScalar Fixes & Improvements:

Here are some fixes/improvements that have been made to the SimpleScalar processor simulator. This started out as a repository for fixes that I contributed, but it now contains contributions from others as well.

• Annotations in SimpleScalar 2.0

  Instruction annotations don't work out of the box in SimpleScalar 2.0 due to a bug in their implementation in the GNU assembler provided as part of the SimpleScalar-specific GNU binutils package. Here is the original message I posted to the mailing list, and here is a context diff for binutils-2.5.2/gas/config/tc-ss.c (the only file that needs to be changed).

  CAVEAT EMPTOR: This fix only preserves annotations on instructions that are not macro-expanded by the assembler into sequences of other instructions. I know for a fact that integer loads and simple ALU operations can be annotated using this fix. However, there are other instructions which are treated by the assembler as macros and the expansion can lead to the dropping of annotations. Grep the GNU assembler sources for "macro" to see which instructions are treated in this way. There is no easy fix for this, since you need to define what it means to annotate a macro instruction and this depends on what the annotation is meant to communicate to the simulator. Certain others here at Wisconsin have patched the assembler to annotate macros in a way suitable for their particular research. Let me know if you need this kind of capability and I will forward you to them.

  
  

• The Alpha ISA of SimpleScalar 3.0

  UPDATE:

  These source-code changes have been merged by Todd Austin into a new pre-release of Simplescalar version 3.0b, now available via FTP as a gzipped tar file. The release also contains a number of other fixes, so please download the SS-3.0b pre-release instead of using the files and diffs provided below.

  Expansion of supported Alpha ISA: The Alpha simulator included in SimpleScalar 3.0a does not implement the entire Alpha ISA, in particular it does not implement instructions that were introduced in the Alpha 21164 (EV5), 21164A (EV56) and 21264 (EV6). These instructions occur in binaries compiled on the more recent 21164A/21264 machines and are generally handled via traps/emulation on Alphas that do not support these instructions (or they are treated as a no-ops in a forward-compatible manner). However, the simulator does not handle them and hence I could not use binaries compiled on spanking new Alphas with the latest compilers and all optimizations turned on. This happens even if one uses the vendor compiler with the "-arch ev4" option since the standard libraries include such instructions.

  Using the Alpha Architecture Handbook Rev.4 from Digital(sorry, Compaq)'s Alpha Documentation Library, I expanded SimpleScalar's Alpha ISA definition file to include ALL user-mode instructions in the Alpha ISA (as of the 21264). A total of 40 new instructions have been added. Some of these (such as prefetch hints) are currently no-ops and VAX FP instructions generate "unimplemented" faults. But all 21164A and 21264 instruction extensions (BWX,CIX,FIX,MVI) are implemented and are working to the best of my knowledge.

  Misc bug fixes/additions: Apart from this ISA expansion, the files below contain some bug fixes and improvements that allowed people to run Alpha binaries on Simplescalar-3.0a. The fixes include supporting some additional system calls and making conditional branches use the correct number of bits in an offset (which was breaking a few programs).
  Here's what you need to get:

  1. An explanation of the changes and what's been tested
  2. The latest target-alpha/alpha.def file,
     OR a context diff from the original file,
     OR a context diff from Todd's updated definition which included the BWX extensions
     OR a context diff from my updated definition which defined all the Alpha instructions
  3. A modified target-alpha/alpha.h file, OR a context diff from the original file.
  4. An updated target-alpha/syscall.c.

  More and better benchmarks: We need something more "real-world" than SPEC95 (heck, those are nearly 5 years old). Here are some applications that run on Simplescalar-Alpha thanks to it being able to run unmodified statically-linked Alpha binaries:

  • X-based graphics apps: X Windows versions of DooM, POVRay, Xanim and XLock. Originally released by Todd Austin and available from here.

  • Quake: Vanilla X and OpenGL-on-X Alpha/OSF versions of Quake 1 based on the source code recently released under the GPL by iD Software. Grab them from the links below. Both gzipped tar files contain READMEs explaining the modifications and how to use the Alpha binaries with Simplescalar. IMPORTANT: You need to grab the latest ISA (alpha.def, alpha.h) and syscall (syscall.c) definition files from the links above in order to use these Quake binaries.
    • Modified Quake 1.06 shareware distribution with Alpha binaries, 13.2MB, here is the enclosed README
    • Modified Quake source code that generates Alpha binaries, 2.7MB, here is the enclosed README
    (Quake is a registered trademark of iD Software)

  Annotations and Binary Editing for Simplescalar-Alpha: Currently SimpleScalar does not provide annotation support for the Alpha simulator because the 32-bit instruction width provides no space for stuffing annotations. However, one could use some of the new 21264 instructions (e.g., the multimedia instructions part of the MVI extensions) as dummy annotation-holders. Other options include faking annotations by keeping a per-PC annotation table in the simulator which is consulted to get/set annotations, or by storing annotations in an unused section of the executable and modifying the Simplescalar loader to process this section.
  On a related note, some folks in Arizona have developed an Alpha binary optimizer called Alto. They claim to do a better job than Alpha's OM tool and the best thing of all is that they provide the full source code for their tool. With some work, Alto can be converted into a binary editor for Alpha executables allowing you to traverse a program and insert/modify individual instructions.

If you have any problems obtaining or using these fixes, please let me know via e-mail.

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