如何在Linux架构上即时列出C代码中可用的所有功能/符号？

Question

假设main.c使用来自共享库的符号和在中声明的局部函数main.c。

有没有一种很好的，优雅的方法来在运行时打印所有可用函数名称和符号的列表？

由于数据已加载到.code段中，因此应该可行。

Answer 1

由于我同样需要在运行时检索所有已加载的符号名称，因此我根据R
..的答案进行了一些研究。因此，这里是ELF格式的Linux共享库的详细解决方案，该解决方案可与我的gcc 4.3.4一起使用，但也希望与新版本一起使用。

我主要使用以下资源来开发此解决方案：

• ELF手册页
• 一些示例代码（在搜索“ dl_iterate_phdr”时找到了它）

这是我的代码。我使用自解释变量名并添加了详细注释以使其易于理解。如果有什么错误或遗漏，请让我知道…（编辑：我刚刚意识到问题是C的，而我的代码是C
++的。但是，如果省略向量和字符串，它也应适用于C ）

#include <link.h>
#include <string>
#include <vector>

using namespace std;

/* Callback for dl_iterate_phdr.
 * Is called by dl_iterate_phdr for every loaded shared lib until something
 * else than 0 is returned by one call of this function.
 */
int retrieve_symbolnames(struct dl_phdr_info* info, size_t info_size, void* symbol_names_vector) 
{

    /* ElfW is a macro that creates proper typenames for the used system architecture
     * (e.g. on a 32 bit system, ElfW(Dyn*) becomes "Elf32_Dyn*") */
    ElfW(Dyn*) dyn;
    ElfW(Sym*) sym;
    ElfW(Word*) hash;

    char* strtab = 0;
    char* sym_name = 0;
    ElfW(Word) sym_cnt = 0;

    /* the void pointer (3rd argument) should be a pointer to a vector<string>
     * in this example -> cast it to make it usable */
    vector<string>* symbol_names = reinterpret_cast<vector<string>*>(symbol_names_vector);

    /* Iterate over all headers of the current shared lib
     * (first call is for the executable itself) */
    for (size_t header_index = 0; header_index < info->dlpi_phnum; header_index++)
    {

        /* Further processing is only needed if the dynamic section is reached */
        if (info->dlpi_phdr[header_index].p_type == PT_DYNAMIC)
        {

            /* Get a pointer to the first entry of the dynamic section.
             * It's address is the shared lib's address + the virtual address */
            dyn = (ElfW(Dyn)*)(info->dlpi_addr +  info->dlpi_phdr[header_index].p_vaddr);

            /* Iterate over all entries of the dynamic section until the
             * end of the symbol table is reached. This is indicated by
             * an entry with d_tag == DT_NULL.
             *
             * Only the following entries need to be processed to find the
             * symbol names:
             *  - DT_HASH   -> second word of the hash is the number of symbols
             *  - DT_STRTAB -> pointer to the beginning of a string table that
             *                 contains the symbol names
             *  - DT_SYMTAB -> pointer to the beginning of the symbols table
             */
            while(dyn->d_tag != DT_NULL)
            {
                if (dyn->d_tag == DT_HASH)
                {
                    /* Get a pointer to the hash */
                    hash = (ElfW(Word*))dyn->d_un.d_ptr;

                    /* The 2nd word is the number of symbols */
                    sym_cnt = hash[1];

                }
                else if (dyn->d_tag == DT_STRTAB)
                {
                    /* Get the pointer to the string table */
                    strtab = (char*)dyn->d_un.d_ptr;
                }
                else if (dyn->d_tag == DT_SYMTAB)
                {
                    /* Get the pointer to the first entry of the symbol table */
                    sym = (ElfW(Sym*))dyn->d_un.d_ptr;


                    /* Iterate over the symbol table */
                    for (ElfW(Word) sym_index = 0; sym_index < sym_cnt; sym_index++)
                    {
                        /* get the name of the i-th symbol.
                         * This is located at the address of st_name
                         * relative to the beginning of the string table. */
                        sym_name = &strtab[sym[sym_index].st_name];

                        symbol_names->push_back(string(sym_name));
                    }
                }

                /* move pointer to the next entry */
                dyn++;
            }
        }
    }

    /* Returning something != 0 stops further iterations,
     * since only the first entry, which is the executable itself, is needed
     * 1 is returned after processing the first entry.
     *
     * If the symbols of all loaded dynamic libs shall be found,
     * the return value has to be changed to 0.
     */
    return 1;

}

int main()
{
    vector<string> symbolNames;
    dl_iterate_phdr(retrieve_symbolnames, &symbolNames);

    return 0;
}