Good day, I am trying to debug this C code which interacts with XDMA device:

#include <fstream>
#include <iostream>
#include <unistd.h>

int main()
{
    std::ofstream output_;
    const char* output_name = "/dev/xdma/card0/h2c0";

    output_.exceptions(std::ios::failbit | std::ios::badbit);
    output_.rdbuf()->pubsetbuf(nullptr, 0);
    output_.open(output_name, std::ios::binary | std::ios::out);

    std::streamoff offset = 0x1e00000;
    output_.seekp(offset, std::ios::beg);

    const char buf[1] = "";
    std::streamsize size = 1;
    auto pos = output_.tellp();

    output_.write(buf, size); // <--- IOSTREAM ERROR

    output_.seekp(pos   size, std::ios::beg);
    return 0;
}

But this program fails on output_.write(buf, size); - with quite a vague error message:

terminate called after throwing an instance of 'std::__ios_failure'
  what():  basic_ios::clear: iostream error
Aborted (core dumped)

And, if I wrap this output_.write(buf, size); in a try & catch block:

    try {
        output_.write(buf, size);
    }
    catch (std::system_error& e) {
        std::cerr << e.code().message() << "(" << e.code().value() << ")\n";
        return 1;
    }

it changes to iostream error(1). This doesn't tell a failure reason... I know for sure that I can write to 0x1e00000 offset, because the alternative C code is working flawlessly. So the error is in C code or library. How to get more debug info?

CodePudding user response：

Although I didn't succeed in getting more debug info, the solution was to downgrade the XDMA driver, which provides /dev/xdma/card0/h2c0 device, from v2017.1.47 to the older v2017.0.45 version (which needed a custom patch to work on new OS). Unfortunately these new drivers are really buggy...