Platform Compatibility

ID

csharp.platform_compatibility

Severity

low

Remediation Complexity

medium

Remediation Risk

low

Remediation Effort

medium

Resource

Reliability

Language

CSharp

Tags

platform, reliability

Description

Reports calls to a small allow-listed set of Windows-only .NET APIs from code that does not carry a [SupportedOSPlatform("windows")] attribute on the enclosing method or type. Such calls compile cleanly on any platform but throw PlatformNotSupportedException at runtime on Linux and macOS.

Rationale

EventLog, Microsoft.Win32.Registry, PerformanceCounter, System.Drawing.Printing.PrinterSettings and a few others are Windows-only. The .NET 5+ analyser model uses [SupportedOSPlatform]/[UnsupportedOSPlatform] to mark this explicitly. Code that ignores the marker silently shifts platform-specific behaviour into production.

using System.Diagnostics;
using Microsoft.Win32;
using System.Runtime.Versioning;

public class Logger
{
    public void Write(string msg)
    {
        EventLog.WriteEntry("App", msg);                        // FLAW
    }

    public string Read()
    {
        return (string) Registry.GetValue("HKLM", "Name", "");   // FLAW
    }
}

[SupportedOSPlatform("windows")]
public class WindowsLogger
{
    public void Write(string msg)
    {
        EventLog.WriteEntry("App", msg);                        // OK
    }
}

public class GuardedAtMethod
{
    [SupportedOSPlatform("windows")]
    public void Write(string msg)
    {
        EventLog.WriteEntry("App", msg);                        // OK
    }
}

Remediation

Annotate the enclosing method or class with [SupportedOSPlatform("windows")], or guard the call with OperatingSystem.IsWindows() and let the analyser flow-analyse it. For genuinely cross-platform code, replace the Windows-only API with a portable alternative (e.g. ILogger/Microsoft.Extensions.Logging instead of EventLog).

References