Kan*_*oge 26
由于我有同样的需要在运行时检索所有加载的符号名称,我根据R ..的答案做了一些研究.所以这里是一个详细的解决方案,用于ELF格式的linux共享库,它与我的gcc 4.3.4一起使用,但希望也可以使用更新的版本.
我主要使用以下来源来开发此解决方案:
这是我的代码.我使用自我解释变量名称并添加详细注释以使其可理解.如果出现问题或遗漏,请告诉我...(编辑:我刚刚意识到问题是针对C而我的代码是针对C++的.但是如果你省略了向量和字符串它也应该适用于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;
}
R..*_*R.. 11
在基于动态链接的ELF的系统上,您可以使用一个功能dl_iterate_phdr.如果是这样,它可以用于收集每个加载的共享库文件的信息,并且您获得的信息足以检查符号表.这个过程基本上是:
dl_phdr_info传递给您的结构中获取程序头的地址.PT_DYNAMIC程序头查找_DYNAMIC模块的表.DT_SYMTAB,DT_STRTAB以及DT_HASH项目的_DYNAMIC找到符号列表.DT_HASH仅需要获取符号表的长度,因为它似乎不存储在其他任何地方.你需要的类型应该都在<elf.h>和<link.h>.
我更新了 Kanalpiroge 的答案中的代码，因此它也可以在 DT_HASH 丢失的情况下工作（例如，RHEL）。它适用于 64 位，但修改它以支持 32 位也相对容易。灵感来自这里：https://chromium-review.googlesource.com/c/crashpad/crashpad/+/876879/18/snapshot/elf/elf_image_reader.cc#b512。
#include <link.h>
#include <string>
#include <vector>
using namespace std;
static uint32_t GetNumberOfSymbolsFromGnuHash(Elf64_Addr gnuHashAddress)
{
// See https://flapenguin.me/2017/05/10/elf-lookup-dt-gnu-hash/ and
// https://sourceware.org/ml/binutils/2006-10/msg00377.html
typedef struct
{
uint32_t nbuckets;
uint32_t symoffset;
uint32_t bloom_size;
uint32_t bloom_shift;
} Header;
Header* header = (Header*)gnuHashAddress;
const void* bucketsAddress = (void*)gnuHashAddress + sizeof(Header) + (sizeof(uint64_t) * header->bloom_size);
// Locate the chain that handles the largest index bucket.
uint32_t lastSymbol = 0;
uint32_t* bucketAddress = (uint32_t*)bucketsAddress;
for (uint32_t i = 0; i < header->nbuckets; ++i)
{
uint32_t bucket = *bucketAddress;
if (lastSymbol < bucket)
{
lastSymbol = bucket;
}
bucketAddress++;
}
if (lastSymbol < header->symoffset)
{
return header->symoffset;
}
// Walk the bucket's chain to add the chain length to the total.
const void* chainBaseAddress = bucketsAddress + (sizeof(uint32_t) * header->nbuckets);
for (;;)
{
uint32_t* chainEntry = (uint32_t*)(chainBaseAddress + (lastSymbol - header->symoffset) * sizeof(uint32_t));
lastSymbol++;
// If the low bit is set, this entry is the end of the chain.
if (*chainEntry & 1)
{
break;
}
}
return lastSymbol;
}
/* 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_GNU_HASH && sym_cnt == 0)
{
sym_cnt = GetNumberOfSymbolsFromGnuHash(dyn->d_un.d_ptr);
}
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;
}