To catch fatal errors like Segmentation Fault during runtime I write a custom SignalHandler that will print a stack trace to console and into a log file.
To achieve this I use (as hundreds before me) the backtrace() and backtrace_symbols() functions in combination with addr2line.
A call to backtrace_symbols() produces following output:
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]
I need to pass the offset to addr2line to get my module name and line number.
$ addr2line -C -a -s -f -p -e ./D098_Mainboard_Software 0xb1a79
0x00000000000b1a79: HandleBacktraceSignals at SignalModule.c:492
However, in some modules (especially cpp ones) I get the offset as a combination off sybols and hex, like _Z13MainboardInit7QString+0xf3
I can resolve the symbol to hex with a call to nm:
$ nm Mainboard_Software | grep _Z13MainboardInit7QString
00000000000a3fec T _Z13MainboardInit7QString
Now I can add these two hex numbers, pass them to addr2line and get my module name and line number, even demangled if I want to:
$ addr2line -C -a -s -f -p -e ./D098_Mainboard_Software 0xa40df
0x00000000000a40df: MainboardInit(QString) at MainboardInit.cpp:219
But I want to do the last two steps during runtime. Is there a way to resolve these symbols (e.g. _Z13MainboardInit7QString+0xf3) during runtime so that I can pass them directly to addr2line?
My program consists of both .c and.cpp modules.
Took me a while but with Linux, one can use the dlfcn.h GNU library.
Just be sure to define _GNU_SOURCE above all header file includes.
Beware this include will make your program POSIX nonconform.
For the linker flags add -ldl for both architectures and -g3 for x86 and -g3, -funwind-tables,-mapcs-frame for 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;
}
}
Calls to this function will produce output like this on console:
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 ??:?