This single-header project implements dynamic library symbol interposition for both macOS and Linux. This allows you to build shared libraries that can intercept calls to library functions for special handling or replacement. The syntax is the same for both Linux and Mac, despite the fact that these platforms support library interposition with very different mechanisms. This implementation makes use of C++11 features, so it will not work with older versions of C++.
To use the interpose tool, just #include <interpose.hh> in the source file where you will implement the replacement functions. A simple replacement function looks like this:
INTERPOSE(malloc)(size_t sz) {
fprintf(stderr, "Caught a call to malloc(%lu)\n", sz);
return real::malloc(sz);
}This line declares a replacement function for malloc that logs the result, then passes the call on to the real malloc implementation. For this to work, the malloc symbol must be defined (by including stdlib.h). The replacement function is type-checked against the declared function, so compilation will fail if you try to replace malloc with a function that takes an int parameter. This helps prevent accidental type mismatch errors, but you can explicitly bypass this requirement by declaring malloc yourself instead of including the system-wide declaration.
There is an example library in examples/logger that intercepts calls to malloc, free, calloc, and realloc. This library tracks the number of bytes allocated and freed by the program, and prints allocation stats just before the program exits.
Invoking make test in the mentioned directory will build and use the C++ version of the example interposition library, then run the test program with that library preloaded. Invoking make test_c will use the C version of the library instead.
A C-only version is provided in interpose.h, differing in the name of the macro, the arguments passed to it, and the constructed name of the original function:
INTERPOSE_C(void*, malloc, (size_t sz), (sz)) {
fprintf(stderr, "Caught a call to malloc(%zu)\n", sz);
return Real__malloc(sz);
}For interposing functions returning void, the macro INTERPOSE_C_VOID() is provided:
INTERPOSE_C_VOID(free, (void* p), (p)) {
fprintf(stderr, "Caught a call to free()\n");
Real__free(p);
}Using INTERPOSE_C(void, <remaining arguments...>) may compile, but expands to code that violates constraint #1 of C99 and C11 "6.8.6.4 The return statement".
MIT License
Copyright (c) 2017 Charlie Curtsinger
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
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