Process.ProcessName can return full path in spite of the documentation

[k15tfu]

Hi!

It turned out that sometimes Process.GetCurrentProcess().ProcessName can return full path to the executable in spite of the documentation: The ProcessName property holds an executable file name, such as Outlook, that does not include the .exe extension or the path. (as per https://docs.microsoft.com/en-us/dotnet/api/system.diagnostics.process.processname?view=netframework-4.8).

Looking into the code, I see that System.Diagnostics.Process.ProcessName internally uses ves_icall_System_Diagnostics_Process_ProcessName_internal, which in its turn calls mono_w32process_module_get_name, and in some cases it uses mono_w32process_get_name:

mono/mono/metadata/w32process-unix.c

Lines 1027 to 1036 in 8266c56

	if (procname_ext == NULL) {
	mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_PROCESS, "%s: Can't find procname_ext from procmods %p", __func__, handle);
	/* If it's *still* null, we might have hit the
	* case where reading /proc/$pid/maps gives an
	* empty file for this user.
	*/
	procname_ext = mono_w32process_get_name (pid);
	if (!procname_ext)
	mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_PROCESS, "%s: Can't find procname_ext from proc_get_name %p pid %d", __func__, handle, pid);
	}

which is based on readlink /proc/self/exe:

mono/mono/metadata/w32process-unix-default.c

Lines 78 to 89 in 8266c56

	memset (buf, '\0', sizeof(buf));
	filename = g_strdup_printf ("/proc/%d/exe", pid);
	#if defined(HAVE_READLINK)
	if (readlink (filename, buf, 255) > 0) {
	ret = g_strdup (buf);
	}
	#endif
	g_free (filename);
	if (ret != NULL) {
	return(ret);
	}

In my case this leads to No such file or directory error when I'm trying to create the logs located here: /tmp/SomeLogsFromProcessWithName{Process.GetCurrentProcess().ProcessName}#{Process.GetCurrentProcess().Id}.log

[ThomasKuehne]

I don't see how mono_w32process_get_name could try to open /proc/self/exe,

Could you please identify what file name is actually causing No such file or directory by

1. using a debugger or
2. strace (available in almost all Linux distributions):
   strace --follow-forks --output=traces /usr/bin/mono test.exe
   and then searching the traces file for the relevant ENOENT (No such file or directory) error.

[k15tfu]

@ThomasKuehne Hi! There are two errors, the first is that we use too short buffer when parsing maps file, and the second is that in this case we fallback to /proc/self/exe and doesn't extract an executable name from it. Here is simple repro:

1. Create a project with this:

using System;
using System.Diagnostics;

namespace ConsoleApplication1
{
    internal class Program
    {
        public static void Main(string[] args)
        {
            Console.WriteLine(Process.GetCurrentProcess().ProcessName);
        }
    }
}

2. Build, and move to a directory with long full path (235 characters in my case)
3. Run

user@h:~/tmp2/ConsoleApplication1/bin/Debug/abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789/abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789/abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789$ mono ConsoleApplication1.exe
/usr/bin/mono-sgen