如何在addr2line运行时的偏移量中解析backtrace_symbols（）中的cpp符号

Question

为了在运行时捕获像分段错误这样的致命错误，我编写了一个自定义SignalHandler，它将堆栈跟踪打印到控制台并进入日志文件。

为了实现这一点，我使用backtrace()和backtrace_symbols()函数backtrace()与我之前的数百个backtrace_symbols()结合addr2line 。

对backtrace_symbols()调用会产生以下输出：

Obtained 8 stack frames.
./Mainboard_Software(+0xb1af5) [0x56184991baf5]
./Mainboard_Software(+0xb1a79) [0x56184991ba79]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x12dd0) [0x7fe72948bdd0]
./Mainboard_Software(causeSIGFPE+0x16) [0x561849918a10]
./Mainboard_Software(_Z13MainboardInit7QString+0xf3) [0x56184990e0df]
./Mainboard_Software(main+0x386) [0x5618499182a3]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xeb) [0x7fe727fd909b]
./Mainboard_Software(_start+0x2a) [0x5618498ff0aa]

我需要将偏移量传递给addr2line以获取我的模块名称和行号。

$ addr2line -C -a -s -f -p -e ./D098_Mainboard_Software 0xb1a79
0x00000000000b1a79: HandleBacktraceSignals at SignalModule.c:492

但是，在某些模块（特别是cpp）中，我将偏移量作为sybols和hex的组合，如_Z13MainboardInit7QString+0xf3

我可以通过调用nm将符号解析为十六进制：

$ nm Mainboard_Software | grep _Z13MainboardInit7QString
00000000000a3fec T _Z13MainboardInit7QString

现在我可以添加这两个十六进制数字，将它们传递给addr2line并获取我的模块名称和行号，如果我想：

$ addr2line -C -a -s -f -p -e ./D098_Mainboard_Software 0xa40df
0x00000000000a40df: MainboardInit(QString) at MainboardInit.cpp:219

但我想在运行时执行最后两个步骤。 有没有办法在运行时解析这些符号（例如_Z13MainboardInit7QString+0xf3 ），以便我可以直接将它们传递给addr2line？ 我的程序包含.c和.cpp模块。

Answer 1

您可以使用库cxxabi对符号运行时进行解码：

#include <cxxabi.h>
//...
char *symbolName = "_Z13MainboardInit7QString";
int st;
char* cxx_sname = abi::__cxa_demangle
(
      symbolName,
      nullptr,
      0,
      &st
);

返回的cxx_name数组包含demangled符号。

通过使用括号作为开始和结束分隔符的简单解析，可以从初始字符串恢复地址（基址和偏移量）。

Answer 2

花了一些时间，但是使用Linux，可以使用dlfcn.h GNU库。 只需确保在所有头文件包含上面定义_GNU_SOURCE 。 注意这包括会使你的程序POSIX不合格。

对于连接标志添加-ldl两种架构和-g3 x86和-g3 ， -funwind-tables ， -mapcs-frame为ARM。

#define _GNU_SOURCE

#include <execinfo.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

#include <dlfcn.h>
#include <gnu/lib-names.h>

#define STACK_FRAMES_BUFFERSIZE (int)128

static void * STACK_FRAMES_BUFFER[128];
static void * OFFSET_FRAMES_BUFFER[128];
static char   EXECUTION_FILENAME[32] = "Mainboard_Software";


/*-----------------------------------------------------------------------------------*/
/*
 * Function will attempt to backtrace the signal cause by collecting the last called addresses.
 * The addresses will then be translated into readable stings by addr2line
 */

static void PrintBacktrace(void)
{
   const char errorString[] = "Offset cannot be resolved: No offset present?\n\0?";
   char       printArray[100] = {0};
   size_t     bufferEntries;
   char **    stackFrameStrings;
   size_t     frameIterator;

   //backtrace the last calls
   bufferEntries = backtrace(STACK_FRAMES_BUFFER, STACK_FRAMES_BUFFERSIZE);
   stackFrameStrings = backtrace_symbols(STACK_FRAMES_BUFFER, (int)bufferEntries);

   //print the number of obtained frames
  sprintf(printArray,"\nObtained %zd stack frames.\n\r", bufferEntries);
  (void)write(STDERR_FILENO, printArray, strlen(printArray));

   //iterate over addresses and print the stings
   for (frameIterator = 0; frameIterator < bufferEntries; frameIterator++)
   {
#if __x86_64__
      //calculate the offset on x86_64 and print the file and line number with addr2line
      OFFSET_FRAMES_BUFFER[frameIterator] = CalculateOffset(stackFrameStrings[frameIterator]);
      if(OFFSET_FRAMES_BUFFER[frameIterator] == NULL)
      {
         (void)write(STDERR_FILENO, errorString, strlen(errorString));
      }
      else
      {
         Addr2LinePrint(OFFSET_FRAMES_BUFFER[frameIterator]);
      }
#endif
#if __arm__
      //the address itself can be used on ARM for a call to addr2line
      Addr2LinePrint(STACK_FRAMES_BUFFER[frameIterator]);
#endif
   }
   free (stackFrameStrings);
 }

/*-----------------------------------------------------------------------------------*/
/*
 * Use add2line on the obtained addresses to get a readable sting
 */
static void Addr2LinePrint(void const * const addr)
{
  char addr2lineCmd[512] = {0};

  //have addr2line map the address to the relent line in the code
  (void)sprintf(addr2lineCmd,"addr2line -C -i -f -p -s -a -e ./%s %p ", EXECUTION_FILENAME, addr);

  //This will print a nicely formatted string specifying the function and source line of the address
  (void)system(addr2lineCmd);
}
/*-----------------------------------------------------------------------------------*/
/*
 * Pass a string which was returned by a call to backtrace_symbols() to get the total offset
 * which might be decoded as (symbol + offset). This function will return the calculated offset
 * as void pointer, this pointer can be passed to addr2line in a following call.
 */
void *  CalculateOffset(char * stackFrameString)
{
   void *     objectFile;
   void *     address;
   void *     offset = NULL;
   char       symbolString[75] = {'\0'};
   char       offsetString[25] = {'\0'};
   char *      dlErrorSting;
   int        checkSscanf = EOF;
   int        checkDladdr = 0;
   Dl_info    symbolInformation;

   //parse the string obtained by backtrace_symbols() to get the symbol and offset
   parseStrings(stackFrameString, symbolString, offsetString);

   //convert the offset from a string to a pointer
   checkSscanf = sscanf(offsetString, "%p",&offset);

   //check if a symbol string was created,yes, convert symbol string to offset
   if(symbolString[0] != '\0')
   {
      //open the object (if NULL the executable itself)
      objectFile = dlopen(NULL, RTLD_LAZY);
      //check for error
      if(!objectFile)
      {
         dlErrorSting = dlerror();
         (void)write(STDERR_FILENO, dlErrorSting, strlen(dlErrorSting));
      }
      //convert sting to a address
      address = dlsym(objectFile, symbolString);
      //check for error
      if(address == NULL)
      {
         dlErrorSting = dlerror();
         (void)write(STDERR_FILENO, dlErrorSting, strlen(dlErrorSting));
      }
      //extract the symbolic information pointed by address
      checkDladdr = dladdr(address, &symbolInformation);

      if(checkDladdr != 0)
      {
         //calculate total offset of the symbol
         offset = (symbolInformation.dli_saddr - symbolInformation.dli_fbase) + offset;
         //close the object
         dlclose(objectFile);
      }
      else
      {
         dlErrorSting = dlerror();
         (void)write(STDERR_FILENO, dlErrorSting, strlen(dlErrorSting));
      }
   }

   return checkSscanf != EOF ? offset : NULL;
}
/*-----------------------------------------------------------------------------------*/
/*
 * Parse a string which was returned from backtrace_symbols() to get the symbol name
 * and the offset. 
 */

void parseStrings(char * stackFrameString, char * symbolString, char * offsetString)
{
   char *        symbolStart = NULL;
   char *        offsetStart = NULL;
   char *        offsetEnd = NULL;
   unsigned char stringIterator = 0;

   //iterate over the string and search for special characters
   for(char * iteratorPointer = stackFrameString; *iteratorPointer; iteratorPointer++)
   {
      //The '(' char indicates the beginning of the symbol
      if(*iteratorPointer == '(')
      {
         symbolStart = iteratorPointer;
      }
      //The '+' char indicates the beginning of the offset
      else if(*iteratorPointer == '+')
      {
         offsetStart = iteratorPointer;
      }
      //The ')' char indicates the end of the offset
      else if(*iteratorPointer == ')')
      {
         offsetEnd = iteratorPointer;
      }

   }
   //Copy the symbol string into an array pointed by symbolString
   for(char * symbolPointer = symbolStart+1; symbolPointer != offsetStart; symbolPointer++)
   {
      symbolString[stringIterator] = *symbolPointer;
      ++stringIterator;
   }
   //Reset string iterator for the new array which will be filled
   stringIterator = 0;
   //Copy the offset string into an array pointed by offsetString
   for(char * offsetPointer = offsetStart+1; offsetPointer != offsetEnd; offsetPointer++)
   {
      offsetString[stringIterator] = *offsetPointer;
      ++stringIterator;
   }
}

调用此函数将在控制台上生成如下输出：

Obtained 11 stack frames.
0x00000000000b1ba5: PrintBacktrace at SignalModule.c:524
0x00000000000b1aeb: HandleBacktraceSignals at SignalModule.c:494
0x0000000000012dd0: ?? ??:0
0x00000000000aea85: baz at testFunctions.c:75
0x00000000000aea6b: bar at testFunctions.c:70
0x00000000000aea5f: foo at testFunctions.c:65
0x00000000000aea53: causeSIGSEGV at testFunctions.c:53
0x00000000000a412f: MainboardInit(QString) at MainboardInit.cpp:218
0x00000000000ae2f3: main at Main.cpp:142 (discriminator 2)
0x000000000002409b: ?? ??:0
0x00000000000950fa: _start at ??:?