如何在Linux架构上即时列出C代码中可用的所有功能/符号? [英] How to list on-the-fly all the functions/symbols available in C code on a Linux architecture?
问题描述
假定main.c使用来自共享库的符号和在main.c中声明的局部函数.
Assume main.c uses symbols from shared libs and local functions declared in main.c.
是否存在一种很好的，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?
Is there a nice and elegant way to print a list of all the available function names and symbols at run time?
应该有可能，因为数据已加载到.code段.
It should be possible since the data is loaded to the .code segment.
推荐答案
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配合使用，但希望也适用于较新的版本.
Since I had the same need to retrieve all loaded symbol names at runtime, I did some research based upon R..'s answer. So here is a detailed solution for linux shared libraries in ELF format which works with my gcc 4.3.4, but hopefully also with newer versions.
我主要使用以下资源来开发此解决方案:
I mostly used the following sources to develop this solution:
- ELF Manpage
- Some sample code (found it while searching for "dl_iterate_phdr")
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.如果有问题或遗失，请告诉我... (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)
And here's my code. I used self explaining variable names and added detailed comments to make it understandable. If something is wrong or missing, please let me know... ( I just realized that the question was for C and my code is for C++. But if you leave out the vector and the string it should work for C as well)
#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;
}
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