lib_loader

This is my attempt at an rtld (RunTime Link eDitor)

It mostly works... it requires a number of "fixups" to be defined before loading a library.

The way the fixup function code works you can substitute a function for another. If you're library requires the malloc symbol and you want to hook it with something else:

 #include "librtld.h"
 /* ... */
 void* my_malloc(size_t l){ /* ... */ }
 /* ... */
 Anchor malloc_fixup = { "malloc", my_malloc };
 /* ... */
 add_fixup_anchor(&malloc_fixup);

To use a list of anchors, add_fixup_anchor_list expects { NULL, NULL } to be the last Anchor in the list:

 #include <stdlib.h>
 #include "librtld.h"
 /* ... */
 Anchor anchor_list[] = {
	{ "malloc", malloc },
	{ "free", free },
    { NULL, NULL }
 };
 /* ... */
 add_fixup_anchor_list(anchor_list);

The test/zlib/lizb_loader.c has a good example of how to do the fixup.

There isn't an install rule yet, so to use the tests you'll need to do

LD_LIBRARY_PATH=$(pwd)/lib:$LD_LIBRARY_PATH

before running the tests (assuming you're in the root source directory)

To test test_loader:

 run make
 ./test/lib_test/test_loader ./test/lib_test/lib.so

To test libz_loader:

 modify test/zlib/libz_loader.c to include the path to your libz.so
 run make
 to deflate: test zlib/libz_loader < to_compress > ouput_file
 to inflate: test/zlib/libz_loader -d < compressed_file > decompressed_file

Things that need to be done:

 * Write documentation
 * Refactor the code
 * Test everything

If there's an issue where you can't initialize an Anchor for stdout, stdin, or stderr:

 Anchor a = { "stdin", NULL };
 /* ... */
 a.symbol = (void *)stdin;

The reason for this is the standard FILE*s arn't required to be static but they have to be, to be used in an initializer.