Source: elfexe.hh

// ElfExe - adding symbols to running Elf processes
// Copyright (C) 1998,1999 Colin McCormack,
// see LICENSE (MD5 f5220f8f599e5e926f37cf32efe3ab68) for terms
// 	$Id

extern "C" {
#include <glibc-inc/link.h>
#include <glibc-inc/elf.h>
}

extern "C" {
    struct link_map;
}

/** ElfExe - direct meddling in elf executable symbol table to add new symbols
 *
 * this class modifies the symbol table of the currently running
 * process' executable by directly modifying the internal data
 * of the ld-linux and libdl.so libraries.
 *
 * This is regrettable, but the alternative is to beg the glibc
 * `maintainers' to fix bugs they hardly even seem to recognise.
 *
 * The result is a glibc2 version-specific meddling object which will
 * completely die as soon as the internal representation used in libdl.so
 * and ld.so changes.  It will need to be ported to new architectures, and
 * may not even be portable to some.
 */
class ElfExe
{
    // Elf direct meddling
    unsigned int cursymcnt;	// symbol table occupancy
    unsigned int strtablen;	// real strtab size

    ElfW(Addr) orgSymTab;
    const ElfW(Symndx) *orgBuckets;
    const ElfW(Symndx) *orgChain;
    ElfW(Symndx) orgNbuckets;
    ElfW(Addr) orgHash;
    ElfW(Addr) orgStrTab;
    
    static const unsigned int STRTINC = 1024;	// strtab increment
    static const unsigned int SYMTINC = 1024;	// symtab increment

    unsigned char *dupStrTab();
    size_t addStrTab(const char *str);
    unsigned long elf_hash (const unsigned char *name);
    static const size_t elf_buckets[];
    unsigned int nrChain();
    ElfW(Symndx) *mkShadow(int additional = SYMTINC);

    link_map *_so;	// the executable's link_map

public:
    /** create an ElfExe for the current process
     *
     * Permits new symbols to be defined in the current process
     */
    ElfExe();

    /** restore the process' symbol table to a pristine state
     */
    ~ElfExe();

    /** add a global symbol to the executable
     * @param name symbol's mangled name
     * @param value symbol's value
     * @param size symbol's allocation size
     * @param type symbol's STT_ type
     * @param type symbol's STB_ binding (def: STB_GLOBAL)
     * @param section symbol's program .section (def: SHN_ABS)
     */
    void addSym(const char *name, void *value, int size,
            int type, int bind = STB_GLOBAL, int section = SHN_ABS);
};