FITIn is a tool to be used by Valgrind that allows flipping a bit of data at a certain time.

In order to understand when and how FITIn is doing bit flips, please read the following information carefully.

In the source code, you specify which start addresses you want to monitor inside a selected function (default: main).

Whenever FITIn detects a read from a memory beginning at a monitored start address, a counter is increased - even if the data has been loaded into a register.

Next to some other customizable constraints, you can use this counter to schedule bit-flips, performed by the Lua-callback flip_value.

FITIn will also treat reads of memory and registers by syscalls.

To get a better feeling for 'accesses', think of your C code while it is not optimized and spot any reading from a monitored variable.

Things that do not count as access (with a being monitored):

• Copies: b = a;, the copy is one access to a but any access to b is out of scope.
• Identity assignments: a=a;
• Anonymous expressions: (a + b) * c, again there is only one access before the addition.
• Irregular access: ((char*)&a) + b), as this is not touching the start address at execution time (but a is wide enough, e.g. by int a;).

Please have a look at fortran/README.

FITIn recommends annotating source code in order to work conveniently.

Please include fi_client.h from the Valgrind include-directory. For setting up monitoring of access to memory, use one of the following macros:

• FITIN_MONITOR_VARIABLE(var)
• FITIN_MONITOR_MEMORY(addr, size)
• FITIN_BREAKPOINT
• FITIN_BREAKPOINTi(a1,..,ai) (integer messages)

Then compile the source code. Deactivating any optimization levels is strongly recommended, as optimazations by the compiler may render this tool useless.

Start FITIn by specifying --tool=fitin followed by options and the program to run.

Control over FITIn has been moved to Lua scripts completely. You need to provide the path to a Lua script by --control-script=. Please read the file sample.lua for a documentation of callbacks and limitations of the Lua-runtime.

For additional options of Valgrind and FITIn, please consult --tool=fitin --help.

By increasing the verbosity Level of Valgrind, you will also receive additional information about FITIn.

Have a look at the tests folder. Please note that the tests are not built by the ordinary make command and require Ruby if used by the test suite.

For more information, please consult the README inside.

• If accessing data from memory, the tool focuses on matching start addresses being monitored. For uses of different alignments, use FITIN_MONITOR_MEMORY instead of FITIN_MONITOR_VARIABLE for every byte that may be a start address.
• Limited support for rotating register files: not respected for IRDirty helpers.

Please post anything like that to https://github.com/MarcelHB/valgrind-fitin/issues