I have a following setup. Although my working setup deals with ARM compiler Real View Developer Suite (RVDS) 3.2 on a Windows host, the situation could be generic for any other C compiler on any host.
I build a ARM library (static library - .a file) of C code using RVDS 3.2 compiler toolchain on Windows host. Then I link this library with an application using an ARM-Linux compiler toolchain on a Linux host, to get a ARM executable. Now when I try to debug this generated ARM executable on Linux using gdb, by trying to put a breakpoint in some function which is present in the library that is linked, gdb is not able to put breakpoint there citing source not found. So I manually copied all the source files(*.c) used to create the library in the Linux folder where the executable file is present. Still gdb fails to put a breakpoint.
So now I started thinking:
How can I do source level debugging of this library which I create on Windows using a different compiler chain by launching the executable which is generated by linking this library to an application, in gdb. Is it possible? How can I do it? Is there any compiler option in RVDS compiler toolchain to enable this library source level debug?
Do I need to copy the source files to linux in exactly same folder structure as that is present in windows for those source files?
You could try to see if mimicking the exact same directory structure works. If you're not sure what directory structure the compiler annotated in the debug info in the executable, you can always look at it with dwarfdump (on linux).
First, GDB does not need any source to put breakpoints on functions; so your description of what is actually happening is probably inaccurate. I would start by verifying that the function you want to break on is actually there in the binary:
nm /path/to/app | grep function_desired
Second, to do source level debugging, GDB needs debug info in a format GDB understands. On Linux this generally means DWARF or STABS. It is quite possible that your RVDS compiler does not emit such debug info; if so, source level debugging will not be possible.
Did you build the library with debugging enabled (-g option)? Without that, there would be difficulties identifying lines etc.
I've found that -fPIC will cause this sort of issue, but the only work around I've found is to not use -fPIC when I want to debug.
Related
I am patching code into my car's ECU. This has a Motorola MC68376 processor, so I'm using the appropriate CPU32 instruction set.
I want to continue to write in assembly code so that I can explicitly manage control registers, RAM access and allocation, as well as copying code structures which are already in use.
My first patch was successfully compiled in EASy68k, but that program does not support the full instruction set for the CPU32. For example, the DIVS.L command is not supported, so I cannot take a quotient of a 32-bit value.
Thus, before writing my own compiler out of sheer incompetence with available tools, I'm looking for an easier path. I read that gcc has the capability to compile code for the CPU32, but I have failed to get it to work.
I'm using MinGW's gcc (6.3.0) and Eclipse (2020-03). I added the '-mcpu32' or '-march=cpu32' flags to the compiler call, according to:
https://gcc.gnu.org/onlinedocs/gcc/M680x0-Options.html
Unfortunately this returns an error:
gcc: error: unrecognized command line option '-mcpu32'; did you mean '-mcpu='?
or
error: bad value (cpu32) for -march= switch
May I please have some advice for making this work? Does anyone know of a better CPU32 compiler that works with Eclipse?
I did not understand that gcc is conventionally distributed as binary files that are compiled with different functionality to suit the needs of a given user.
There seem to be two paths forward:
1) compile my own cross-compiler version of GCC
2) download a pre-compiled cross-compiler version of GCC
I chose to follow route 2).
I began the process of installing the 'Windows Subsystem for Linux' and Ubuntu 20.04 Focal Fossa, because I found a pre-made compiler that should be capable of performing cross compilation for the m68k processor: "gobjc-10-m68k-linux-gnu"
https://ubuntu.pkgs.org/20.04/ubuntu-universe-i386/gobjc-10-m68k-linux-gnu_10-20200411-0ubuntu1cross1_i386.deb.html
While I was installing that, I also found an m68k-elf gcc toolchain that is pre-compiled for windows 10:
https://gnutoolchains.com/m68k-elf/
I played with the latter for much of today. Although I was unable to get the toolchain integrated well with Eclipse, it works from the command line to compile a *.s assembly code file. This includes compatibility with the '-mcpu32' flag that I wanted at the outset.
There is still a lot for me to figure out, even after floundering through learning gcc's assembler directives (https://www.eecs.umich.edu/courses/eecs373/readings/Assembler.pdf) and the differences in gcc's assembly syntax compared to the MC68k reference manual (https://www.nxp.com/files-static/archives/doc/ref_manual/M68000PRM.pdf).
I can even convert the code section of the output file to be a proper s-record by using objcopy with the '-O srec' and '--only-section=.text' flags. This helps me patch the code into my ECU.
Thus I've answered my original question.
I have to compile a simple binary for a very old Linux system. I have no gcc/build libs available on the target machine but I do have access to the machine.
I am having trouble compiling the code on my machine and having it execute on target machine.
I am copying libc.so to my local machine and trying to compile and link the program so that it will execute on the target machine.
I have copied the libc from the target machine to mine and tried compiling it with my target executable.
this has gotten closes to a successful execution:
gcc -nostdlib ./libc-[version].so myFile.c -emain -o outfile.out
upon execution a very simple PoC test program runs, and then seg faults upon exit. the actual program simply seg faults.
It seems I have somewhat of a lack of understanding of linking. Any help?
It seems I have somewhat of a lack of understanding of linking.
You do. A "normal" user-level program doesn't start executing at main, it starts at _start.
The _start symbol typically comes from crt0.o file (part of libc), and knows how to "interface" between the way the kernel supplies arguments, and the way main expects to find them. It also initializes various data that must be initialized before main runs (e.g. stdio streams).
What you want to do then is:
Find out the actual link command that gcc main.o performs. You can do so by adding the -v flag.
Replicate such command, providing crt0.o and other input files, appropriate for your version of target libc.
It might be easier to spin up a VM with the OS matching your target (and with old tools that target it), and build your program inside of that VM.
Otherwise you'll likely have to set up a full cross-compiler environment (which includes libc and all other libraries you need). This is not a trivial proposition, and is certainly not accomplished by copying libc.so from the target machine. But it is well-documented and is certainly doable (with some skill).
I'm a student doing research involving extending the TM capabilities of gcc. My goal is to make changes to gcc source, build gcc from the modified source, and, use the new executable the same way I'd use my distro's vanilla gcc.
I built and installed gcc in a different location (not /usr/bin/gcc), specifically because the modified gcc will be unstable, and because our project goal is to compare transactional programs compiled with the two different versions.
Our changes to gcc source impact both /gcc and /libitm. This means we are making a change to libitm.so, one of the shared libraries that get built.
My expectation:
when compiling myprogram.cpp with /usr/bin/g++, the version of libitm.so that will get linked should be the one that came with my distro;
when compiling it with ~/project/install-dir/bin/g++, the version of libitm.so that will get linked should be the one that just got built when I built my modified gcc.
But in reality it seems both native gcc and mine are using the same libitm, /usr/lib/x86_64-linux-gnu/libitm.so.1.
I only have a rough grasp of gcc internals as they apply to our project, but this is my understanding:
Our changes tell one compiler pass to conditionally insert our own "function builtin" instead of one it would normally use, and this is / becomes a "symbol" which needs to link to libitm.
When I use the new gcc to compile my program, that pass detects those conditions and successfully inserts the symbol, but then at runtime my program gives a "relocation error" indicating the symbol is not defined in the file it is searching in: ./test: relocation error: ./test: symbol _ITM_S1RU4, version LIBITM_1.0 not defined in file libitm.so.1 with link time reference
readelf shows me that /usr/lib/x86_64-linux-gnu/libitm.so.1 does not contain our new symbols while ~/project/install-dir/lib64/libitm.so.1 does; if I re-run my program after simply copying the latter libitm over the former (backing it up first, of course), it does not produce the relocation error anymore. But naturally this is not a permanent solution.
So I want the gcc I built to use the shared libs that were built along with it when linking. And I don't want to have to tell it where they are every time - my feeling is that it should know where to look for them since I deliberately built it somewhere else to behave differently.
This sounds like the kind of problem any amateur gcc developer would have when trying to make a dev environment and still be able to use both versions of gcc, but I had difficulty finding similar questions. I am thinking this is a matter of lacking certain config options when I configure gcc before building it. What is the right configuration to do this?
My small understanding of the instructions for building and installing gcc led me to do the following:
cd ~/project/
mkdir objdir
cd objdir
../source-dir/configure --enable-languages=c,c++ --prefix=/home/myusername/project/install-dir
make -j2
make install
I only have those config options because they seemed like the ones closest related to "only building the parts I need" and "not overwriting native gcc", but I could be wrong. After the initial config step I just re-run make -j2 and make install every time I change the code. All these steps do complete without errors, and they produce the ~/project/install-dir/bin/ folder, containing the gcc and g++ which behave as described.
I use ~/project/install-dir/bin/g++ -fgnu-tm -o myprogram myprogram.cpp to compile a transactional program, possibly with other options for programs with threads.
(I am using Xubuntu 16.04.3 (64 bit), within VirtualBox on Windows. The installed /usr/bin/gcc is version 5.4.0. Our source at ~/project/source-dir/ is a modified version of 5.3.0.)
You’re running into build- versus run-time linking differences. When you build with -fgnu-tm, the compiler knows where the library it needs is found, and it tells the linker where to find it; you can see this by adding -v to your g++ command. However when you run the resulting program, the dynamic linker doesn’t know it should look somewhere special for the ITM library, so it uses the default library in /usr/lib/x86_64-linux-gnu.
Things get even more confusing with ITM on Ubuntu because the library is installed system-wide, but the link script is installed in a GCC-private directory. This doesn’t happen with the default GCC build, so your own GCC build doesn’t do this, and you’ll see libitm.so in ~/project/install-dir/lib64.
To fix this at run-time, you need to tell the dynamic linker where to find the right library. You can do this either by setting LD_LIBRARY_PATH (to /home/.../project/install-dir/lib64), or by storing the path in the binary using -Wl,-rpath=/home/.../project/install-dir/lib64 when you build it.
i'm tryin to debug (actually i just want to understand the program on assembly level) a program. Usin gdb is ok but in tui mode it would be just great, unfortunately i get an error when i'm debuggin in tui while displaying the assembly and source code (-g option in gcc) mode sayin: error while reading shared library symbols
I can run the program if i do not show the assembly code but that is not what i want, i really want to step through every assembly line to fully understand the program. Also, when i try this with si sometimes i get an error for example in printf but that's another story
so any tips? Note:this is not a bug of my program, i tried this with other programs
Your shared libraries were not compiled with symbols enabled. You need to look for, usually, "debug" versions of gcc libraries (or your other libraries that you are linking against). If you have custom libraries that you are building, add the -g option to the gcc commands that are being run to compile them.
Using MacPorts i have just installed arm-elf-gcc on to my MacBook Pro. This worked flawlessly and all seems to run fine.
However, after compiling a simple hello world test program in C and C++ and trying to run either on the target board (an ARM9 based board running Debian Linux) they immediately seg fault.
I'm a bit stuck as how to go about debugging this, as the target board has limited tools available and no gdb. I have successfully built and run other code using a Linux hosted cross compiler so it should work.
Any ideas?
Following the suggestion I have built and run gdbserver, I get the following in gdb on the host:
Program received signal SIGSEGV, Segmentation fault.
0x00000000 in ?? ()
I thought it may be a problem with the standard c libs so I removed any calls and have just an empty main that return 0, it is compiled with -Wall -g hello-arm.cpp -static. As a test I compiled the same source with a Linux hosted cross compiler and it runs and exits fine. The only difference I can see is the that Linux compiled version is over twice the size and the difference in output from the file command:
arm-elf-gcc: ELF 32-bit LSB executable, ARM, version 1, statically linked, not stripped
arm-*-linux: ELF 32-bit LSB executable, ARM, version 1, statically linked, for GNU/Linux 2.4.18, not stripped
The usual method of debugging in this situation is to run gdbserver on the target board, and connect to it (via ethernet) with gdb running on a host computer.
Alternately, you could try comparing the assembly in a Mac-compiled "Hello World" program and a (working) Linux-compiled one to see what's different.
After digging around for a couple of days I am starting to understand a bit more about embedded compilers. I wasn't really sure of the difference between arm-elf-gcc installed via MacPorts and the arm-unknown-linux toolchain I had installed on my Linux box. I just came across a pdf titled "An introduction to the GNU compiler" which contains the following paragraph:
Important: Using the GNU Compiler to
create your executable is not quite
the same as using the GNU Linker,
arm-elf-ld, yourself. The reason is
that the GNU Compiler automatically
links a number of standard system
libraries into your executable. These
libraries allow your program to
interact with an operating system, to
use the standard C library functions,
to use certain language features and
operations (such as division), and so
on. If you wish to see exactly which
libraries are being linked into the
executable, you should pass the
verbose flag
-v to the compiler.
This has important implications for
embedded systems! Such systems do not
usually have an operating system.
This means that linking in the system
libraries is almost always
meaningless: if there is no operating
system, for example, then calling the
standard printf function does not make
much sense.
So when I get back to my dev machine later I will determine the libraries linked in with the Linux build and add them to the arm-elf-gcc build.
I'll update this when I have more information but I just want to document my findings in case any one else has these problems.