c - 查找数据段的地址范围

Question

作为一个编程练习，我正在用 C 编写一个标记和清除垃圾收集器。我希望扫描数据段(全局变量等)以查找指向已分配内存的指针，但我不知道如何获取该段的地址范围。我怎么能这样做？

Answer 1

如果您在 Windows 上工作，那么 Windows API 可以为您提供帮助。

//store the base address the loaded Module
dllImageBase = (char*)hModule; //suppose hModule is the handle to the loaded Module (.exe or .dll)

//get the address of NT Header
IMAGE_NT_HEADERS *pNtHdr = ImageNtHeader(hModule);

//after Nt headers comes the table of section, so get the addess of section table
IMAGE_SECTION_HEADER *pSectionHdr = (IMAGE_SECTION_HEADER *) (pNtHdr + 1);

ImageSectionInfo *pSectionInfo = NULL;

//iterate through the list of all sections, and check the section name in the if conditon. etc
for ( int i = 0 ; i < pNtHdr->FileHeader.NumberOfSections ; i++ )
{
     char *name = (char*) pSectionHdr->Name;
     if ( memcmp(name, ".data", 5) == 0 )
     {
          pSectionInfo = new ImageSectionInfo(".data");
          pSectionInfo->SectionAddress = dllImageBase + pSectionHdr->VirtualAddress;

          **//range of the data segment - something you're looking for**
          pSectionInfo->SectionSize = pSectionHdr->Misc.VirtualSize;
          break;
      }
      pSectionHdr++;
}

将 ImageSectionInfo 定义为，

struct ImageSectionInfo
{
      char SectionName[IMAGE_SIZEOF_SHORT_NAME];//the macro is defined WinNT.h
      char *SectionAddress;
      int SectionSize;
      ImageSectionInfo(const char* name)
      {
            strcpy(SectioName, name); 
       }
};

这是一个完整的、最小的 WIN32 控制台程序，您可以在 Visual Studio 中运行，它演示了 Windows API 的使用:

#include <stdio.h>
#include <Windows.h>
#include <DbgHelp.h>
#pragma comment( lib, "dbghelp.lib" )

void print_PE_section_info(HANDLE hModule) // hModule is the handle to a loaded Module (.exe or .dll)
{
   // get the location of the module's IMAGE_NT_HEADERS structure
   IMAGE_NT_HEADERS *pNtHdr = ImageNtHeader(hModule);

   // section table immediately follows the IMAGE_NT_HEADERS
   IMAGE_SECTION_HEADER *pSectionHdr = (IMAGE_SECTION_HEADER *)(pNtHdr + 1);

   const char* imageBase = (const char*)hModule;
   char scnName[sizeof(pSectionHdr->Name) + 1];
   scnName[sizeof(scnName) - 1] = '\0'; // enforce nul-termination for scn names that are the whole length of pSectionHdr->Name[]

   for (int scn = 0; scn < pNtHdr->FileHeader.NumberOfSections; ++scn)
   {
      // Note: pSectionHdr->Name[] is 8 bytes long. If the scn name is 8 bytes long, ->Name[] will
      // not be nul-terminated. For this reason, copy it to a local buffer that's nul-terminated
      // to be sure we only print the real scn name, and no extra garbage beyond it.
      strncpy(scnName, (const char*)pSectionHdr->Name, sizeof(pSectionHdr->Name));

      printf("  Section %3d: %p...%p %-10s (%u bytes)\n",
         scn,
         imageBase + pSectionHdr->VirtualAddress,
         imageBase + pSectionHdr->VirtualAddress + pSectionHdr->Misc.VirtualSize - 1,
         scnName,
         pSectionHdr->Misc.VirtualSize);
      ++pSectionHdr;
   }
}

// For demo purpopses, create an extra constant data section whose name is exactly 8 bytes long (the max)
#pragma const_seg(".t_const") // begin allocating const data in a new section whose name is 8 bytes long (the max)
const char const_string1[] = "This string is allocated in a special const data segment named \".t_const\".";
#pragma const_seg() // resume allocating const data in the normal .rdata section

int main(int argc, const char* argv[])
{
   print_PE_section_info(GetModuleHandle(NULL)); // print section info for "this process's .exe file" (NULL)
}

This page如果您对 DbgHelp 库的其他用途感兴趣，可能会有所帮助。

你可以在这里阅读PE图像格式，详细了解它。一旦理解了 PE 格式，您就可以使用上面的代码，甚至可以修改它以满足您的需要。

• PE格式

Peering Inside the PE: A Tour of the Win32 Portable Executable File Format

An In-Depth Look into the Win32 Portable Executable File Format, Part 1

An In-Depth Look into the Win32 Portable Executable File Format, Part 2

• Windows API 和结构

IMAGE_SECTION_HEADER Structure

ImageNtHeader Function

IMAGE_NT_HEADERS Structure

我认为这会在很大程度上帮助你，剩下的你可以自己研究:-)

顺便说一句，你也可以看到这个线程，因为所有这些都与此有某种关系:

Scenario: Global variables in DLL which is used by Multi-threaded Application