Add Android support for choc_DetectDebugger

[manol-o]

Hi,

I am using this code quite a while and I had no problems.
Would be cool if it could be added to develop:

#elif CHOC_ANDROID

#include <sys/ptrace.h>
#include <unistd.h>
#include <fcntl.h>
#include <string>
#include <android/log.h>

inline bool choc::isDebuggerActive()
{
    // Method 1: Check TracerPid in /proc/self/status (similar to Linux)
    auto readTracerPid = []() -> int
    {
        int tracerPid = 0;
        int fd = open("/proc/self/status", O_RDONLY);
        if (fd == -1)
            return 0;

        char buf[512];
        ssize_t n = read(fd, buf, sizeof(buf)-1);
        close(fd);
        if (n <= 0)
            return 0;

        buf[n] = '\0';
        std::string status(buf);
        std::string tracerPidStr = "TracerPid:";
        size_t pos = status.find(tracerPidStr);

        if (pos != std::string::npos)
        {
            size_t lineEnd = status.find('\n', pos);
            std::string line = status.substr(pos, lineEnd - pos);
            try
            {
                tracerPid = std::stoi(line.substr(tracerPidStr.length()));
            }
            catch (...) {}
        }
        return tracerPid;
    };

    return readTracerPid() > 0;
}

Thanks!

[julianstorer]

The linux version that already exists seems to be a much cleaner version of practically the same thing.. I can't see why you'd write an (uglier!) version of readStatusFileItem() rather than just re-use that function for both platforms..?
Is there some non-obvious difference between them that I'm not spotting?

[manol-o]

using #elif CHOC_LINUX || CHOC_ANDROID does not work in android studio, but the code I posted works.

I asked gemmini here is what it says:

Yes, you have found a bug in how choc::file::loadFileAsString handles "special" files like those in /proc.

The reason the Linux code fails on Android (and actually on Linux too, if you strictly use that specific helper) is that /proc files report a file size of 0.

The Root Cause: loadFileAsString checks size first
I found the implementation of choc::file::loadFileAsString in choc_Files.h, and it does this:

// Inside choc_Files.h
stream.open (filename, std::ios::binary | std::ios::ate); // Open at the end
auto fileSize = stream.tellg();                           // Get size
if (fileSize == 0)
    return {};                                            // <--- FAILS HERE

Files in /proc are "virtual" files generated by the kernel on the fly. They do not sit on a disk, so they report a size of 0 bytes until you actually start reading them. Because loadFileAsString sees a size of 0, it assumes the file is empty and returns immediately.
​

Why the "Self-Contained" code works
Your raw Android code uses the standard C read() function:

char buf[512];
ssize_t n = read(fd, buf, sizeof(buf)-1);

This simply asks the OS "give me whatever bytes you have right now," ignoring the reported file size. This is the correct way
to read from /proc.

Solution
You cannot use choc::file::loadFileAsString for /proc files. You should stick with your "self-contained" version for Android.

If you really want to clean it up and use CHOC style, you would need to add a new helper function to choc that reads without checking size, like this:

// You'd need a custom helper like this for proc files
inline std::string readProcFile(const std::string& path)
{
    std::ifstream f(path);
    // Read strictly by character or line, ignoring size
    return std::string(std::istreambuf_iterator<char>(f),
                       std::istreambuf_iterator<char>()); 
}

Verdict: Keep your CHOC_ANDROID block separate and use the manual read() code you already have. It is robust and correct for this specific task.

Tbh I don't know if this is all true but at least I know that the raw ugly code I pasted works and #elif CHOC_LINUX || CHOC_ANDROID does not