I've been using WASM via emscripten for a few weeks now and had been making good progress, until this error:
exception thrown: RuntimeError: function signature mismatch,RuntimeError: function signature mismatch
This started happening in code that previously worked and seems to be something to do with WASMs lack of support for 64bit integers in javascript and the offsets used in file management. I've made an isolated case:
#include <iostream>
int main(int argc, char const *argv[])
{
char test[30];
std::cout << __LINE__ << std::endl;
FILE *f = fopen("minimal_call_dispatch.cpp","ra");
std::cout << __LINE__ << std::endl;
fseek(f, 100, SEEK_SET);
std::cout << __LINE__ << std::endl;
fclose(f);
std::cout << __LINE__ << std::endl;
return 0;
}
building with:
call emcc -o ./test.js test_file.cpp -s WASM=1 -s NO_EXIT_RUNTIME=1 -std=c++1z
Which outputs '6\n8\n' before failing on 'fseek' due to the mentioned error.
Somewhere along the line, I suspect that wasm is trying to use headers that communicate with javascript that have 64bit integers instead of 32bit ones but I can't see how that could have happened.
I'm going to try re-installing emscripten but even if that works, I'd like to get a better idea of what's causing this.
As a work around, does anybody know how to get emcc to ignore worries over 64bit integers and silently convert them to 32bit? I'm not looking to address more than 3gigs of ram, after all.
You got the error simply because your code is wrong.
You really don't need to worry about 32bit/64bit stuff. The current WebAssembly spec do not have 64-bit machine and it only have 32-bit addresses (but it supports 64-bit integer i64 internally and calculates 64-bit integers well. It just doesn't have 64-bit addresses.)
This means that the compiler is already knows the target machine is 32-bit and size_t will be 32-bit as will.
In the comments, I asked if you want to open the file or want to create the file. This is important because using "ra" with fopen() will cause segmentation fault when the file doesn't exist because of r flag!
Okay, lets try this in the native environment.
g++ test_file.cpp -o test.out
running ./test.out will prints the following if test_file.cpp doesn't exist:
6
8
[2] 14464 segmentation fault (core dumped) ./test.out
So your code is wrong, but why Emscripten throws the error differently? When you use emcc without debugging flags like -g, it will have the minimized environment that doesn't catch errors like segfault because such smart runtime will increase the binary size which is critical in the web environment. As a result the runtime keeps running ignoring segfualt and it will end up with a random error. So function signature mismatch doesn't mean anything.
You can build it using debugging-related options:
emcc -o ./test.html test_file.cpp -s WASM=1 -std=c++1z \
-g4 -s ASSERTIONS=2 -s SAFE_HEAP=1 -s STACK_OVERFLOW_CHECK=1 \
--source-map-base http://your_server_ip:port/
Then opening test.html you will see the correct error now:
exception thrown: RuntimeError: abort(segmentation fault) at Error
Now you won't get the misleading errors like signature mismatch :)
By the way, replace fopen("minimal_call_dispatch.cpp","ra"); with fopen("minimal_call_dispatch.cpp","a"); will fix the error.
With the correct --source-map-base server IP settings, you will have a better debugging experience. For example, you will get the source test_file.cpp in the browser so that you can set breakpoints to the .cpp file.
Have fun with debugging :)
Related
Lets take this very simple program here for example:
// test.cpp
#include <string>
#include <iostream>
using namespace std;
int main() {
string str = "Hello";
cout << str << endl;
return 0;
}
now I compile this code with g++ compiler:
g++ -g test.cpp -o test.exe
now I am trying to debug this with gdb:
gdb test.exe
after I set breakpoint on main and then reach the line return 0, I try to see what is in the string str. But I cannot print it in the console. It says <error reading variable>. Not only in gdb console, even Visual Studio Code UI using gdb gives the same output.
Here is a screenshot of my console:
I have searched for this everywhere and the only relevant question I found was this, which did not work.
I also found this post on github VS Code repo issues. The fix suggested there might work I am not sure, I cannot find the setting that he suggested on my Windows 11 machine.
How do I read the value in the string in debug mode?
Edit
After #ssbssa suggested me to update my gcc, I used MSYS2 to get the latest gcc, g++, and gdb versions. Now I have gdb 12.1. Now it is not showing the old error anymore but now it says "Converting character sets: Invalid argument". Still struggling to get it to work.
First run your program with gdb like so:
gdb test.exe
Now inside the command line interface run the command:
set charset UTF-8
This should temporarily fix your problem. The only inconvenience might be that you need to run this line every time you debug on your command prompt with GDB.
I noticed that you are also using Visual Studio Code. You can install C++ extensions for VS Code and there you can add the command set charset UTF-8 in the launch.json setupCommands array as shown here. This way you can debug your application faster.
I am new to C++ and want to print out a double value. It is not that I actually need to print that value, I just want to know what is going wrong here.
This is my code (HelloWorld.cpp):
#include <iostream>
int main() {
double i = 5.5;
std::cout << i << std::endl;
return 0;
}
Executing this with the debugger attached results in the following error:
Thread 1 hit Breakpoint 1, main () at src/HelloWorld.cpp:4
4 double i = 5.5;
Thread 1 received signal SIGSEGV, Segmentation fault.
0x00000000929ba260 in ?? ()
When I put a breakpoint in there, creating and assigning the variable is no problem. The error only occurs once the program is supposed to print that value. Executing the exe without the debugger results in no output at all. The same happens when I replace the double with a long double or float. Printing anything else works fine (Strings, char, int, short, etc.).
I am using Visual Studio Code and MinGW (x86_64-8.1.0-posix-seh-rt_v6-rev0). VS Code is using following files for compilation / debugging:
c_cpp_properties.json
launch.json
tasks.json
And here you can see the complete output, in case that helps.
Any Idea what I am doing wrong here? Thank you.
EDIT:
When compiling manually using g++ -g .\src\HelloWorld.cpp -std=c++11 -o HelloWorld.exe (or just g++ .\src\HelloWorld.cpp -o HelloWorld.exe) and running that from the console, the same happens (no output).
I installed MinGW from here using the following settings:
Version: 8.1.0
Architecture: x86_64
Threads: posix
Exception: seh
Build revision: 0
EDIT 2:
Found the problem. There was an old version of gcc lurking in my PATH (maybe from Visual Studio or MSSQL Server?). I just move the current gcc to the top of PATH and now it's working fine. Thank you all for your help!
As many pointed out, this should usually work. The problem was with my setup: I had an old version of gcc somewhere in my PATH variable (version 4.1). Moving the path of the newer version to the beginning of PATH resolves the issue. Thank you all for helping.
To check weather the same happens to you you can do the following: execute g++ --version in your project directory. Compare this with the output of g++.exe --version when you are in the directory where gcc is installed (for me, this was C:\Program Files\mingw-w64\x86_64-8.1.0-posix-seh-rt_v6-rev0\mingw64\bin).
I am using a bash shell on my Mac OS X. I have fortran95 compiler installed in /sw/bin/gfortran. every time I attempt to access the compiler, I receive
the error:
"Segmentation fault: 11". I cannot call any programs the regular way
i.e. "gfortran program.f90 -o executable_name "
I am not sure about the problem. Even simple programs which print "hello world" to screen will not work.
May be a problem with your installation as already mentioned. A couple things I would try:
Make sure the shared libraries it is compiled against are being found:
otool -L /sw/bin/gfortran
Compile with some switches that might give you more helpful info. I found using the backtrace option really helps especially to debug seg. faults. You might try to compile with some options such as:
gfortran -g -fbounds-check -Wall -fbacktrace program.f90
I am trying to compile the following program:
#include <iostream>
int main(){
std::cout << "Hello, world!";
return 0;
}
When I compile it, I get this message:
C:\programs>g++ test.cpp
Info: resolving std::cout by linking to __imp___ZSt4cout (auto-import)
c:/mingw/bin/../lib/gcc/mingw32/4.5.0/../../../../mingw32/bin/ld.exe: warning: a
uto-importing has been activated without --enable-auto-import specified on the c
ommand line.
This should work unless it involves constant data structures referencing symbols
from auto-imported DLLs.
The build succeeds and the executable runs as expected, but this warning still irritates me. I expect a successful build to be completely silent. This message gives the false impression that there's something wrong with my code.
I can silence this error with g++ -Xlinker --enable-auto-import test.cpp, but this is undesirable, as it triples the number of characters I need to type to compile a program.
Questions:
Why does this warning appear for the simplest of programs? i don't expect cryptic warnings when I compile Hello World.
Is it possible to silence this warning without passing the flag to the linker every time? An option in a config file hidden somewhere in c:\mingw, perhaps? Or maybe I missed an "automatically enable auto-import" checkbox during installation?
Possibly Relevant Specs
GCC Version 4.5.0
ld.exe Version 2.20.51.20100613
Windows XP Service Pack 3
I used to face same problem as you do with g++. I solved this irritating problem just now. Here is how I come to the solution, step-by-step:
On Windows, you can create an alias of g++ with all given options which you want to use with g++. Say, for example, you want to create an alias s++ of g++ -enable-auto-import, then you run this on cmd as:
C:\>doskey s++=g++ -enable-auto-import
This creates an alias called s++. But this alias will not take any command line argument, which means, you cannot write this:
C:\>s++ filename.cpp //it is not working
To make it work, if you've to tell the alias to accept command line arguments while creating it, so here is how it is done:
C:\>doskey s++=g++ -enable-auto-import $*
Please note the $* at the right, which indicates that now s++ can take command line argument:
C:\>s++ filename.cpp //yayyyy..its working now, without giving any warnings!
But you may not prefer to create the alias everytime you open cmd. In that case, you can create a shortcut of cmd.
For example, I created a shortcut called Console and in the Target textbox of shortcut window, I wrote this:
C:\WINDOWS\System32\cmd.exe /K doskey s++=g++ -enable-auto-import $*
And since this is too long (horizontally), one screenshot was not able to capture the entire command. I took two screenshots so that you could see yourself how I did it:
Left part of the command
Right part of the command
For more information on creating aliases on windows, see this:
Creating aliases on Windows
I did some reading and it looks like it might be related to the mingw32 dll not having dllimport attributes defined.
Perhaps there is a patch or you can rebuild mingw32 yourself and add them?
Here is the code I have- not sure why I am getting this error message:
$ ./main.cpp "hello" "is"
./main.cpp: line 4: syntax error near unexpected token `('
./main.cpp: line 4: `int main(int argc, char *argv[]){'
It compiles fine in g++, but when I run it, I get the above error. Any idea why? Here is my complete code..
#include <iostream>
#include <fstream>
int main(int argc, char *argv[]){
for(int i = 0; i < argc; i++){
std::cout << argc << " : " << argv[i] << '\n';
}
if (argc != 2){
std::cout << "\nUSAGE: 2 command line arguments please." << std::endl;
std::cout << "\n (1) Input file with raw event scores.\n (2) Output file to write into.";
}
// open the font file for reading
std::string in_file = argv[1];
std::ifstream istr(in_file.c_str());
if (!istr) {
std::cerr << "ERROR: Cannot open input file " << in_file << std::endl;
}
return 0;
}
You have to run the compiled program, not the source code:
$ g++ -o main main.cpp
$ ./main "hello" "is"
3 : ./main
3 : hello
3 : is
USAGE: 2 command line arguments please.
(1) Input file with raw event scores.
(2) Output file to write into.ERROR: Cannot open input file hello
Your example is trying to execute C++ code as a shell script, which isn't going to work. As you can see from the output of my test run of your program here, you still have some bugs to work out.
As both the other answers say, you're running it as a shell script, implicitly using /bin/sh.
The first two lines starting with # are treated by the shell as comments. The third line is blank, and does nothing. The fourth line is interpreted as a command int, but parentheses are special to the shell, and are not being use correctly here. There probably isn't an int command in your $PATH, but the shell doesn't get a chance to report that because it chokes on the syntax error.
None of these details are particularly important; the problem is that you're executing the program incorrectly. But it might be interesting to see why those specific error messages are printed.
And it appears that you've done something like chmod +x main.cpp; otherwise the shell would have refused to try to execute it in the first place. Making a C++ source file executable isn't going to cause any real harm (as long as it's readable and writable), but it's not at all useful, and as you've seen it delayed the detection of your error. If you do chmod -x main.cpp, and then try ./main.cpp again, you'll get a "Permission denied" error instead.
As Carl's answer says, you need to execute the executable file generated by the compiler, not the C++ source file. That's why there's a compiler. The compiler (well, actually the linker) will automatically do the equivalent of chmod +x on the executable file it generates.
The file command will tell you what kind of file something is, which affects what you can do with it. For example, using your code on my system, after running g++ main.cpp -o main:
$ file main.cpp
main.cpp: ASCII C program text
$ file main
main: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.24, BuildID[sha1]=0xacee0dfd9ded7aacefd679947e106b500c2cf75b, not stripped
$
(The file command should have recognized main.cpp as C++ rather than as C, but sometimes it guesses wrong.)
"ELF" is the executable format used by my system; the file contains executable machine code plus some other information. The pre-installed commands on the system use the same format.
The details may differ on your system -- and will differ substantially on non-Unix-like systems such as MS Windows. For example, on Windows executable files are normally named with a .exe extension.
The compiler, by default, creates an executable called "a.out", so you want to do:
$ a.out "hello" "is"
Typing "./main.cpp" is trying to execute the C++ source file, probably as a shell script