How do I analyze a program s core dump file with GDB when it has command-line parameters

Question

My program operates like this   exe -p param1 -i param2 -o param3   It crashed and generated a core dump file  core pid   I want to analyze the core dump file by  gdb   exe -p param1 -i param2 -o param3 core pid   But GDB recognizes the parameters of the EXE file as GDB s input   How do I analyze a core dump file in this situation

User · Answer

From RMS s GDB debugger tutorial   prompt  gt  myprogram Segmentation fault  core dumped  prompt  gt  gdb myprogram      gdb  core core pid       Make sure your file really is a core image -- check it using file

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Just skip the parameters  GDB doesn t need them   gdb   exe core pid

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Simply type the command     gdb  lt Binary gt   lt codeDump gt    Or    gdb  lt binary gt     gdb  core  lt coreDump gt    There isn t any need to provide any command line argument  The code dump generated due to an earlier exercise

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objdump   gdb minimal runnable example TL DR   GDB can be used to find failing line  previously mentioned at  How do I analyze a program  39 s core dump file with GDB when it has command-line parameters  the core file contains the CLI arguments  no need to pass them again objdump -s core can be used to dump memory in bulk  Now for the full educational test setup  main c  include  lt stddef h gt   include  lt stdio h gt   include  lt stdlib h gt   include  lt string h gt   int myfunc int i          int   NULL    i     line 7        return i - 1     int main int argc  char   argv           Setup some memory         char data ptr      quot string in data segment quot       char  mmap ptr      char  text ptr    quot string in text segment quot        void argv      mmap ptr    char   malloc sizeof data ptr    1       strcpy mmap ptr  data ptr       mmap ptr 10     m       mmap ptr 11     m       mmap ptr 12     a       mmap ptr 13     p       printf  quot text addr   p n quot   text ptr       printf  quot data addr   p n quot   data ptr       printf  quot mmap addr   p n quot   mmap ptr           Call a function to prepare a stack trace         return myfunc argc      Compile  and run to generate core  gcc -ggdb3 -std c99 -Wall -Wextra -pedantic -o main out main c ulimit -c unlimited rm -f core   main out  Output  text addr  0x4007d4 data addr  0x7ffec6739220 mmap addr  0x1612010 Segmentation fault  core dumped   GDB points us to the exact line where the segmentation fault happened  which is what most users want while debugging  gdb -q -nh main out core  then  Reading symbols from main out   done   New LWP 27479  Core was generated by    main out   Program terminated with signal SIGSEGV  Segmentation fault   0  0x0000000000400635 in myfunc  i 1  at main c 7 7             int   NULL    i   gdb  bt  0  0x0000000000400635 in myfunc  i 1  at main c 7  1  0x000000000040072b in main  argc 1  argv 0x7ffec6739328  at main c 28  which points us directly to the buggy line 7  CLI arguments are stored in the core file and don t need to be passed again To answer the specific CLI argument questions  we see that if we change the cli arguments e g  with  rm -f core   main out 1 2  then this does get reflected in the previous bactrace without any changes in our commands  Reading symbols from main out   done   New LWP 21838  Core was generated by    main out 1 2   Program terminated with signal SIGSEGV  Segmentation fault   0  0x0000564583cf2759 in myfunc  i 3  at main c 7 7             int   NULL    i     line 7     gdb  bt  0  0x0000564583cf2759 in myfunc  i 3  at main c 7  1  0x0000564583cf2858 in main  argc 3  argv 0x7ffcca4effa8  at main c 2  So note how now argc 3  Therefore this must mean that the core file stores that information  I m guessing it just stores it as the arguments of main  just like it stores the arguments of any other functions  This makes sense if you consider that the core dump must be storing the entire memory and register state of the program  and so it has all the information needed to determine the value of function arguments on the current stack  Less obvious is how to inspect the environment variables  How to get environment variable from a core dump Environment variables are also present in memory so the objdump does contain that information  but I m not sure how to list all of them in one go conveniently  one by one as follows did work on my tests though  p   environ 0   Binutils analysis By using binutils tools like readelf and objdump  we can bulk dump information contained in the core file such as the memory state  Most all of it must also be visible through GDB  but those binutils tools offer a more bulk approach which is convenient for certain use cases  while GDB is more convenient for a more interactive exploration  First  file core  tells us that the core file is actually an ELF file  core  ELF 64-bit LSB core file x86-64  version 1  SYSV   SVR4-style  from    main out   which is why we are able to inspect it more directly with usual binutils tools  A quick look at the ELF standard shows that there is actually an ELF type dedicated to it  Elf32 Ehd e type    ET CORE  Further format information can be found at  man 5 core  Then  readelf -Wa core  gives some hints about the file structure  Memory appears to be contained in regular program headers  Program Headers    Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align   NOTE           0x000468 0x0000000000000000 0x0000000000000000 0x000b9c 0x000000     0   LOAD           0x002000 0x0000000000400000 0x0000000000000000 0x001000 0x001000 R E 0x1000   LOAD           0x003000 0x0000000000600000 0x0000000000000000 0x001000 0x001000 R   0x1000   LOAD           0x004000 0x0000000000601000 0x0000000000000000 0x001000 0x001000 RW  0x1000  and there is some more metadata present in a notes area  notably prstatus contains the PC  Displaying notes found at file offset 0x00000468 with length 0x00000b9c    Owner                 Data size       Description   CORE                 0x00000150       NT PRSTATUS  prstatus structure    CORE                 0x00000088       NT PRPSINFO  prpsinfo structure    CORE                 0x00000080       NT SIGINFO  siginfo t data    CORE                 0x00000130       NT AUXV  auxiliary vector    CORE                 0x00000246       NT FILE  mapped files      Page size  4096                  Start                 End         Page Offset     0x0000000000400000  0x0000000000401000  0x0000000000000000          home ciro test main out     0x0000000000600000  0x0000000000601000  0x0000000000000000          home ciro test main out     0x0000000000601000  0x0000000000602000  0x0000000000000001          home ciro test main out     0x00007f8d939ee000  0x00007f8d93bae000  0x0000000000000000          lib x86 64-linux-gnu libc-2 23 so     0x00007f8d93bae000  0x00007f8d93dae000  0x00000000000001c0          lib x86 64-linux-gnu libc-2 23 so     0x00007f8d93dae000  0x00007f8d93db2000  0x00000000000001c0          lib x86 64-linux-gnu libc-2 23 so     0x00007f8d93db2000  0x00007f8d93db4000  0x00000000000001c4          lib x86 64-linux-gnu libc-2 23 so     0x00007f8d93db8000  0x00007f8d93dde000  0x0000000000000000          lib x86 64-linux-gnu ld-2 23 so     0x00007f8d93fdd000  0x00007f8d93fde000  0x0000000000000025          lib x86 64-linux-gnu ld-2 23 so     0x00007f8d93fde000  0x00007f8d93fdf000  0x0000000000000026          lib x86 64-linux-gnu ld-2 23 so   CORE                 0x00000200       NT FPREGSET  floating point registers    LINUX                0x00000340       NT X86 XSTATE  x86 XSAVE extended state   objdump can easily dump all memory with  objdump -s core  which contains  Contents of section load1    4007d0 01000200 73747269 6e672069 6e207465      string in te  4007e0 78742073 65676d65 6e740074 65787420  xt segment text   Contents of section load15    7ffec6739220 73747269 6e672069 6e206461 74612073  string in data s  7ffec6739230 65676d65 6e740000 00a8677b 9c6778cd  egment    g  gx   Contents of section load4    1612010 73747269 6e672069 6e206d6d 61702073  string in mmap s  1612020 65676d65 6e740000 11040000 00000000  egment            which matches exactly with the stdout value in our run  This was tested on Ubuntu 16 04 amd64  GCC 6 4 0  and binutils 2 26 1

User · Answer

Simple usage of GDB  to debug coredump files   gdb  lt executable path gt   lt coredump file path gt    A coredump file for a  process  gets created as a  core pid  file   After you get inside the GDB prompt  on execution of the above command   type        gdb  where   This will get you with the information  of the stack  where you can analayze the cause of the crash fault  Other command  for the same purposes is        gdb  bt full   This is the same as above  By convention  it lists the whole stack information  which ultimately leads to the crash location

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You can analyze the core dump file using the  gdb  command    gdb - The GNU Debugger   syntax      gdb executable-file core-file   example    gdb out txt core xxx

User · Answer

You can use the core with GDB in many ways  but passing parameters which is to be passed to the executable to GDB is not the way to use the core file  This could also be the reason you got that error  You can use the core file in the following ways   gdb  lt executable gt   lt core-file gt  or gdb  lt executable gt  -c  lt core-file gt  or  gdb  lt executable gt       gdb  core  lt core-file gt    When using the core file you don t have to pass arguments  The crash scenario is shown in GDB  checked with GDB version 7 1 on Ubuntu    For example       crash -p param1 -o param2 Segmentation fault  core dumped    gdb   crash core GNU gdb  GDB  7 1-ubuntu     Core was generated by    crash -p param1 -o param2    lt  lt  lt  lt  lt  See this line shows crash scenario Program terminated with signal 11  Segmentation fault   0    strlen ia32    at    sysdeps i386 i686 multiarch       i586 strlen S 99 99       sysdeps i386 i686 multiarch       i586 strlen S  No such file or directory      in    sysdeps i386 i686 multiarch       i586 strlen S  gdb    If you want to pass parameters to the executable to be debugged in GDB  use --args   For example     gdb --args   crash -p param1 -o param2 GNU gdb  GDB  7 1-ubuntu      gdb  r Starting program   home      crash -p param1 -o param2  Program received signal SIGSEGV  Segmentation fault    strlen ia32    at    sysdeps i386 i686 multiarch       i586 strlen S 99 99       sysdeps i386 i686 multiarch       i586 strlen S  No such file or directory      in    sysdeps i386 i686 multiarch       i586 strlen S  gdb    Man pages will be helpful to see other GDB options

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A slightly different approach will allow you to skip GDB entirely  If all you want is a backtrace  the Linux-specific utility  catchsegv  will catch SIGSEGV and display a backtrace

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It doesn t matter if the executable has arguments or not  To run GDB on any binary with a generated core file  the syntax is below   Syntax  gdb  lt binary name gt   lt generated core file gt  Eg  gdb l3 entity 6290-corefile   Let me take the below example for more understanding   bash-4 1    gdb l3 entity 6290-corefile      Core was generated   by   dir1 dir2 dir3 l3 entity   Program terminated with signal SIGABRT  Aborted     0  1  2  3  4  5  6  7  8  9  10  gdb    From the above output  you can guess something about core  whether it is a NULL access  SIGABORT  etc    These numbers  0 to  10 are the stack frames of GDB  These stack frames are not of your binary  In the above 0 - 10 frames if you suspect anything wrong select that frame   gdb  frame 8   Now to see more details about it    gdb  list     To investigate the issue further  you can print the suspected variable values here at this point in time    gdb  print thread name

[linux] How do I analyze a program's core dump file with GDB when it has command-line parameters?

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