Spec for GetProcessInfo3 IPC command (#3476)

Author: davmason

documentation/design-docs/ipc-protocol.md

@@ -383,6 +383,7 @@ enum class ProcessCommandId : uint8_t
     EnablePerfMap      = 0x05,
     DisablePerfMap     = 0x06,
     ApplyStartupHook   = 0x07
+    ProcessInfo3       = 0x08,
     // future
 }
 ```
@@ -804,7 +805,7 @@ In the event of an [error](#Errors), the runtime will attempt to send an error m
 
 #### Inputs:
 
-Header: `{ Magic; Size; 0x0402; 0x0000 }`
+Header: `{ Magic; Size; 0x0404; 0x0000 }`
 
 There is no payload.
 
@@ -848,6 +849,8 @@ struct Payload
 }
 ```
 
+> Available since .NET 7.0
+
 ### `EnablePerfMap`
 
 Command Code: `0x0405`
@@ -972,6 +975,66 @@ struct Payload
 
 > Available since .NET 8.0
 
+### `ProcessInfo3`
+
+Command Code: `0x0408`
+
+The `ProcessInfo3` command queries the runtime for some basic information about the process. The returned payload is versioned and fields will be added over time.
+
+In the event of an [error](#Errors), the runtime will attempt to send an error message and subsequently close the connection.
+
+#### Inputs:
+
+Header: `{ Magic; Size; 0x0408; 0x0000 }`
+
+There is no payload.
+
+#### Returns (as an IPC Message Payload):
+
+Header: `{ Magic; size; 0xFF00; 0x0000; }`
+
+Payload:
+* `uint32 version`: the version of the payload returned. Future versions can add new fields after the end of the current structure, but will never remove or change any field that has already been defined.
+* `uint64 processId`: the process id in the process's PID-space
+* `GUID runtimeCookie`: a 128-bit GUID that should be unique across PID-spaces
+* `string commandLine`: the command line that invoked the process
+  * Windows: will be the same as the output of `GetCommandLineW`
+  * Non-Windows: will be the fully qualified path of the executable in `argv[0]` followed by all arguments as the appear in `argv` separated by spaces, i.e., `/full/path/to/argv[0] argv[1] argv[2] ...`
+* `string OS`: the operating system that the process is running on
+  * macOS => `"macOS"`
+  * Windows => `"Windows"`
+  * Linux => `"Linux"`
+  * other => `"Unknown"`
+* `string arch`: the architecture of the process
+  * 32-bit => `"x86"`
+  * 64-bit => `"x64"`
+  * ARM32 => `"arm32"`
+  * ARM64 => `"arm64"`
+  * Other => `"Unknown"`
+* `string managedEntrypointAssemblyName`: the assembly name from the assembly identity of the entrypoint assembly of the process. This is the same value that is returned from executing `System.Reflection.Assembly.GetEntryAssembly().GetName().Name` in the target process.
+* `string clrProductVersion`: the product version of the CLR of the process; may contain prerelease label information e.g. `6.0.0-preview.6.#####`
+* `string runtimeIdentifier`: information to identify the platform this runtime targets, e.g. `linux_musl_arm`64, `linux_x64`, or `windows_x64` are all valid identifiers. See [.NET RID Catalog](https://learn.microsoft.com/en-us/dotnet/core/rid-catalog) for more information.
+
+##### Details:
+
+Returns:
+```c++
+struct Payload
+{
+    uint32_t Version;
+    uint64_t ProcessId;
+    LPCWSTR CommandLine;
+    LPCWSTR OS;
+    LPCWSTR Arch;
+    GUID RuntimeCookie;
+    LPCWSTR ManagedEntrypointAssemblyName;
+    LPCWSTR ClrProductVersion;
+    LPCWSTR RuntimeIdentifier;
+}
+```
+
+> Available since .NET 8.0
+
 ## Errors
 
 In the event an error occurs in the handling of an Ipc Message, the Diagnostic Server will attempt to send an Ipc Message encoding the error and subsequently close the connection.  The connection will be closed **regardless** of the success of sending the error message.  The Client is expected to be resilient in the event of a connection being abruptly closed.