I'm a C++ newbie (up to 2.4a on www.learncpp.com) and I'm having trouble debugging in codeblocks. The terminal that opens up when I start debugging says "warning: GDB: Failed to set controlling terminal: Operation not permitted
" and whenever I try to do something, an error appears in the bottom right saying that it couldn't open some file called fileops.c
Here's an image:
GDB is the GNU Debugger. Rest assured,
GDB is not broken.
The pesky warning: GDB: Failed to set controlling terminal: Operation not permitted
has appeared forever in Code::Blocks when you start debugging, due to the way
in which C::B invokes GDB. It is harmless and you can ignore it.
The GDB message fileops.c: No such file or directory appears because
you trying to step into a function that is defined in fileops.c, which
is a source file of the GNU C Library. You cannot step into such functions
because the source code of the GNU C Library that is linked with
your program is not available to GDB.
In general, the source code of any system library that your program is
linked with will not be available to the debugger and similar messages will
appear if you try to step into functions defined in those libraries.
You have to step over those functions and almost always you can do so with a good
will, because the bugs you are looking for are not there. They are in your source
code, which is available to the debugger, and plodding down through all
of the library calls, even if you could, would likely keep you debugging into
old age.
In short, there is nothing the matter. Just step over the functions that you
didn't write.
Related
I'm writing some software that involves Qt, GStreamer, and RTI Connext DDS. On Windows the code hangs at a certain point under certain circumstances.
Just before this happens, the message "Buffer creation failed" is printed on the console. However, this message does not occur in my code, so I assume it is generated by a dependency.
I've attached the Visual Studio debugger to the process, but because DDS is a proprietary library that was compiled in release mode, I have to compile all my code in in release mode, so it appears there is very little information you have access to. I tried to set a breakpoint on printf and puts, but this never triggers.
On Linux I'd poke around with gdb, strace, strings, and what not to try and locate the source of the message, but on Windows I have really no idea how to do these things.
I am trying to write a simple OS, I already wrote a bootloader but now I want to debug it, so I switched from using VirtualBox to QEMU because I saw it had better debugging.
The problem is that after I added the -s parameter to QEMU command and successfully connected via GDB, it says that the symbol table isn't loaded and that I should use the "file" command.
The only difference from what I did to what I saw people on the Internet do, is that they started GDB with gdb vmlinux, but I can't do that because I am not debugging a Linux kernel... so I figured that the issue is that I didn't start GDB with an executable, but using the "file" command on my OS image, and the compiled and linked .out file, tells me it's a "DOS/MBR boot sector", so I can't start GDB with either of them (I tried to do that anyways, but GDB failed).
Help would be appreciated.
EDIT: also, I did assemble the bootloader with the -g and --gstabs+ options.
gdb would like a file so that it can give you symbolic debugging information. For that you will need to give it a file in a format with debug info which corresponds to where your OS ends up in RAM. The "DOS/MBR boot sector" file is a disk image (the BIOS will load part of this into RAM for you, and it will then presumably finish loading code itself).
But gdb will also entirely happily let you do assembly-level debugging; you can just ignore the warning about not having a symbol table, and use the single step instruction, disassemble-from-pc and similar commands:
"disas $pc,+32" disassembles 32 bytes from the current PC
the display command prints after execution stops, so "disp /3i $pc" will print the next 3 instructions every time gdb gets control
"stepi" and "nexti" do single-instruction step/next ("step" and "next" are source-line stepping and require debug info)
I'm studying "Compilers" and we work on Flex to program.
I create *.lex files (with any editor), convert them into lex.yy.c via flex, and then compile to a.exe using gcc.
Writing lex code in an editor like Notepad/Codeblocks/... is not only hard because everything is just BLACK, but also there is no debugging system.
The gcc compiler does tell about errors, but what i'm looking for is something i can go line by line with the code (in runtime) and see what's going on with the variables. Like the command F10 in Visual Studio.
Does anybody know a suitable program for this? Thanks alot
Concerning hightlighting, using gedit(The default GUI editor on Ubuntu and some other Linux variants) or even vim will provide that for you, you don't have to use plain notepad.
As for the debugging, yes there's what's called the GNU Debugger (aka GDB) which allows you to do typical debugging jobs after you've compiled your code, you can step line by line and examine certain variable values.
Before doing that, first compile your program with the gcc flag -g to add debug symbols to the complied result, then run gdb yourProgramName, this will run GDB and you'll be able, using certain commands, to do whatever debugging tasks you want.
I once wrote a little guide to help people get started with GDB, it might be useful.
I'm working on writing an OS and I'm running into problems trying to debug my code. I'm using GDB to connect to Bochs' GDB stub to "remotely" debug my kernel. Connecting works fine, as does loading debugging symbols from the kernel file. I set a breakpoint for the kmain function, which is successfully located, and the debugger breaks correctly (inside my kernel). However, I can't "step" or "next" through my code, nor can GDB apparently determine which line of code is the current line.
When I try to "step", I get the following message: "Cannot find bounds of current function". This is the only error message I get at any point.
My code is being compiled in GCC with the -g flag (I've tried other types of debugging information using GCC options; none have worked.) I have tried looking through the GDB manual , as well as searching for the answer, and I'm totally stumped. Any help would be amazing.
Thanks!
Well, I got debugging working, but I had to switch emulators. I was able to get GDB working with Qemu, even though I also had problems doing that. To get GDB to connect to the Qemu gdbserver, I had to pass the following option to Qemu: "-gdb tcp::1234,ipv4". Took me forever to figure that out... Debugging works perfectly now!
Googling throws up "This is because when you attached to gdbserver, the process under
debug has not completed the C start-up code" http://www.cygwin.com/ml/gdb/2005-03/msg00237.html... http://www.bravegnu.org/gnu-eprog/c-startup.html describes the process for when you are coding for embedded devices, maybe this will help?
If you find the answer please post here as I'd like to know what the solution to the problem is too.
I don't know why but bochs with gdb-stub enabled seems to be picky with the config options. On some system following options will break it:
--enable-x86-64, --enable-vmx
I have an executable built in Windows. I want to pass that .exe to an output file built by Cygwin (DOS version). It is going well up to a point, after which it is showing the following error related to Cygwin dll files (ACL check) .
Program received signal SIGSEGV, Segmentation fault.
0x6108829e in cygwin1!aclcheck () from /usr/bin/cygwin1.dll
(gdb)
Why am I getting this error and where should I look?
Check your code. Since you're already using gdb, bt full shall be your friend. You're possibly passing bad parameters such as invalid pointers to some system call.
It's likely it's not aclcheck where the segfault itself occurs. Cygwin DLLs are normally not shipped with debugging symbols built in. gdb works backwards from the instruction pointer and takes the previous symbol seen. In non-debug builds there are only symbols of exported functions.