C-bind: Dynamic function binding in C !!!

Table of Contents

1. Requirements
2. Usage
   • General
   • SystemV
   • Non-SystemV
3. Examples
4. Compilation
5. Docker
6. CI
7. Documentation
8. Future Plans

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Requirements

Currently C-bind requires pthread to be installed, and requires x86_64. C-bind has only been tested on Ubuntu 18.04, compiled with gcc 7.3.

Usage

General

Includes

To link the C-bind library simply include the header file bind.h.

Note

Passing extra arguments to a bound func will result in them being ignored.

SystemV vs Non-SystemV

The most common calling convention of x86_64 / amd64 is called SystemV. Unless otherwise specified, most major compilers should compile your code to meet this standard. This library provides functions for binding functions that follow the SystemV calling convention; functions that are not compliant have an API for them is provided for them as well. The default API of this library assumes SystemV functions are being bound.

Important notes

1. This library uses a signal internally. By default this is SIGUSR2, however the user may change this whenever. This signal handler is install when-needed and restored when not, so for a single threaded application this is perfectly safe. However, in a multi-threaded enviornment it is important to set this signal to some (valid) unused signal! This can be done with the bind_set_signal_number function.

Thread Safe

Yes, as long as this library is the only thing that invokes the signal set by bind_set_signal_number.

Restrictions

1. This library may not work with variadic functions
2. This library may fail for SystemV if registers other than rdi, rsi, rdx, rcx, r8, and r9 are used to pass arguments. However this is exceedingly rare.
3. This library will only compile for x86_64 / amd64

SystemV

Function Signature

SystemV functions to be bound must return an object of type ret_t (which should be 8 bytes) or smaller; void is also valid. Do not attempt to return a large struct as it may fail! As for the arguments of the function, there are no restrictions except that the function may not be variadic! For more info look in the bind.h file.

Full binding

To fully bind a functon, invoke

bound_func = full_bind( my_func, num_args, arg1, arg2, arg3 );

Here num_args is the number of arguments to pass to be passed to my_func. If more than num_args arguments are passed they will be ignored.

Full binding example

int sum( int a, int b ) { return a + b; }
FullBound bound_func = full_bind( sum, 2, /* Arguments begin */ 1, 2 );
printf( "sum(1,2) = %d", (int) bound_func() );

The output of this code is: sum(1,2) = 3.

Partial binding

To partially bind a function, invoke

bound_func = partial_bind( my_func, num_args, num_args_to_bind, arg1, arg2 );

Here num_args_to_bind is the number of arguments currently being bound!

It is worth noting that fully binding a function via a partial bind is supported.

Partial binding Example

int sum3(int a, int b, int c) { return a + b + c; }
PartBound bound_func = partial_bind( sum3, 3, 2, /* Arguments begin */ 100, 200 );
printf( "Total sum = %d", (int) bound_func(300) );

The output of this code is: Total sum = 600

Non-SystemV

Signature

Non-SystemV functions to be bound must have a unique signature, however when calling them they may be called as standard functions. To bind a function, it must have the following signature:

ret_t my_func( arg_t * args );

A ret_t is simply a void *. A non-void * may be returned via casting so long as it is of equal or lesser size. You can think of args as an array of arguments! The function being bound may not be variadic, consequently, my_func must have a defined maximum number of 'arguments'. That is, my_func must expect that no more num_args number of elements to be passed. For more info look in the bind.h file. Parsing the args array is the job of my_func.

Full binding

To fully bind a function, invoke

bound_func = full_bind( my_func, num_args, arg1, arg2, arg3 );

Here num_args is the number of elements in the args array that my_func expects to be passed. If more arguments than num_args arguments are passed in they will be ignored.

Full binding Example

ret_t sum( arg_t * args ) { return args[0] + args[1]; }
FullBound bound_func = full_systemv_bind( sum, 2, /* Arguments begin */ 1, 2 );
printf( "sum(1,2) = %d", (int) bound_func() );

The output of this code is: sum(1,2) = 3.

Partial binding

To partially bind a function, invoke

bound_func = partial_bind( my_func, num_args, num_args_to_bind, arg1, arg2 );

Here num_args_to_bind is the number of arguments currently being bound!

It is worth noting that fully binding a function via a partial bind is supported.

Partial binding Example

ret_t sum3( arg_t * args ) { return args[0] + args[1] + args[2]; }
PartBound bound_func = partial_systemv_bind( sum3, 3, 2, /* Arguments begin */ 100, 200 );
printf( "Total sum = %d", (int) bound_func(300) );

The output of this code is: Total sum = 600

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Examples

To test the examples first compile the code

git clone https://github.com/zwimer/C-bind && \
mkdir C-bind/build && cd C-bind/build && \
cmake ../examples && make

After that, run your desired test. Either ./test.out (for SystemV tests) or ./test-non-systemv.out.

Compilation

On gcc version7.3, this library is able to compile even with the -O3 flag. If you experience issues however, try compiling at a lower optimization level. See the CMakeLists.txt file in the examples directory for an example.

Docker

A Dockerfile is provided with C-bind and example cases installed and build. The image is hosted here on docker.com. To pull the image just execute:

docker pull zwimer/c-bind

To run the container simply execute:

docker run --rm -it zwimer/c-bind

If you would like to build the container yourself execute:

git clone https://github.com/zwimer/C-bind && \
cd C-bind && \
docker build -t zwimer/c-bind .

CI

Continuous Integration is provided by Travis CI. To view the CI setup, click here.

Documentation

Documentation is stored in on the gh-pages branch and hosted here on zwimer.com. Documentation is generated via doxygen. To manually generate it install doxygen (from apt-get if you have it) then

cd C-bind && doxygen

Future Plans

1. Right now hidden in the internals of how the binding mechanism, the get_stub function maps an entire page of memory per stub generated. Realistically it should only require just a few bytes. This can be done by placing multiple stub functions on the same page.