git mv *.hint -> README.md
There is one exception:
$ find . -name '*.hint' -execdir git mv '{}' README.md \;
git statufatal: destination exists, source=1992/albert/albert.hint, destination=1992/albert/README.md
Looking at the two files they differ quite a bit so I've not changed it.
I'll bring this up on GitHub.
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Most likely to amaze:
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The author wishes to remain anonymous
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Great Britain
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Judges' Comments:
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To build:
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make anonymous
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Try:
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./anonymous anonymous.ten
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Is emulation the sincerest form of flattery? This small program does
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quite a lot of bit twiddling.
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Selected Author's Comments:
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This program is an optimizing dynamic binary translator, allowing you to
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run x86 programs on any machine (x86 or otherwise).
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I have included a simple "10 green bottles" program, already compiled
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for the x86. The program 'ten', and its source (dull) are given as info
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files. Warning: note that the translator screws around with the binary
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you run on it, *will* corrupt the binary to some extent, and may leave
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any program you run on it unusable.
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The build script should give an example command to run.
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Features
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Basic Block Cache: Rather than translating each instruction individually
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the dynamic binary translator generates a translation for an entire
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basic block of subject code. Having translated a block once, the target
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code generated will be stored for the duration that the program is
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running, so as a program runs its performance will improve, as it hits
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cached blocks. This can be clearly observed in the example program,
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'ten'.
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Target Library Linking:
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The program runs dynamically linked elf binaries, and when the subject
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program attempts to make a call to a standard library, the translator
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attempts to make an appropriate call to the native system libraries on
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the target machine. This involves mangling between different calling
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conventions, etc.
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Automatic Endian Detection/Reversal:
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There are various problems raised when attempting to run little endian
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x86 code on a big endian chip, such as a PPC. These problems are dealt
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with in a manner that is entirely transparent to the user.
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Configuration
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Warnings:
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By default the build script should compile the program with a set of
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switches such that while compiling the program it generates one error
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(which I feel is useful advice). The program should generate no further
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compiler errors while it is running (yes, the program can generate
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compiler errors while it is running). If you do not wish to see this
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error, or if the program generates any further error when compiled using
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your C compiler please remove the "warning=..." line from the build
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script.
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Optimization:
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The build script contains a "-O1" switch for the compiler. Increasing
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the optimization level will make the program run *slower*, while
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compiling the program without any optimization will allow it to run
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*faster*.
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Obfuscation
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The most obvious part of the obfuscation is probably the mess of defines
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at the top. This may seem a somewhat tired old obfuscation - however
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since many of these macros are (sometimes only) used by the program once
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it has dynamically recompiled itself, they are only referenced within
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the source code from within strings - and therefore the macros cannot be
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expanded. Furthermore, some of these strings of code are not given as
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strings, but instead are wrapped up in macros that use the "#"
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preprocessor operator to turn them into strings. In the hope throwing a
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few C beautifiers the macro to generate the strings is not contained
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within the source code but instead is passed in on the command line.
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Buried under all this, and the fact that the entire program is just a
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call to exit, there are some nice subtle little obfuscations. For
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example, you may notice that there are a couple of macros that use the
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"##" preprocessor operator to build pairs of functions. One of these
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macros is used to build to pairs of functions of which only one has
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local variables which shadow global variables; so one modifies the
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global state, and the other doesn't.
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There is also quite a nice trick where I wave a magic wand, and a chunk
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of code which should only be run when the program is run for the first
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time (setting the PC to point at main, etc) gets turned into a
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frog^M^M^M^Mstring. The C compiler sees a string by itself in the code,
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thinks "yup, thats a valid C expression", and quietly moves on to the
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next line of code.
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Limitations
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Due to space limitations only a handful of instructions are supported,
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those instructions which are supported may supported in somewhat
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non-conventional ways, chunks of the architecture (e.g. flags) are just
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ignored, the elf loader does not really load the elf binary, the target
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library linking can only pass up to 3 parameters to the target library
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function, etc, etc, etc.
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In short, please consider this a full disclaimer for any bug that may
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turn up - yes the program is unsafe, but it's pretty cool anyway.
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Despite all this, the translator is not exclusively limited to running
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the 'ten' program. Other trivial x86 programs may run on the translator
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- and I have successfully run a wide range of HelloWorld programs,
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including one of last years IOCCC winners, 'tomx'.
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Complete Program
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The fact that the program makes calls to system and execv may imply that
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it is not a complete program in its own right, as it relies on other
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programs. The call to system is a call to ask gcc to recompile the
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translator with a new set of switches, and the call to execv asks for
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the newly compiled program to be executed. I would point out that
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almost every other entry to this competition also require a C compiler
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(well, the published winners at any rate, and I recognize that a few
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don't). There is little real difference between this program and one
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like last years entry 'dhyang'; both are just C programs that generate C
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code as their output.
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Enjoy, thanks!
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