From 1e7cd64f0f71568af0d56d12cdfd8e0156f754d0 Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Tue, 8 Mar 2022 23:12:23 -0500
Subject: [PATCH] Loop through graphics output protocol handles and check each
 one

---
 main.c | 33 ++++++++++++++++++++++++++++++---
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/main.c b/main.c
index 5dd5842..60802ab 100644
--- a/main.c
+++ b/main.c
@@ -22,6 +22,29 @@ static void write_uint(uint32_t n)
     write_string(&s[11u - i]);
 }
 
+static void check_handle(EFI_HANDLE handle)
+{
+    EFI_HANDLE interface = NULL;
+    EFI_STATUS status = g_system_table->BootServices->HandleProtocol(handle,
+            &(EFI_GUID)EFI_GRAPHICS_OUTPUT_PROTOCOL_GUID,
+            &interface);
+    if (EFI_ERROR(status))
+    {
+        write_string(L"Error ");
+        write_uint(status);
+        write_string(L" from HandleProtocol\r\n");
+        return;
+    }
+
+    if (interface == NULL)
+    {
+        write_string(L"NULL interface from HandleProtocol\r\n");
+        return;
+    }
+
+    EFI_GRAPHICS_OUTPUT_PROTOCOL * gop = (EFI_GRAPHICS_OUTPUT_PROTOCOL *)interface;
+}
+
 EFI_STATUS
 efi_main(EFI_HANDLE image_handle, EFI_SYSTEM_TABLE * system_table)
 {
@@ -31,8 +54,6 @@ efi_main(EFI_HANDLE image_handle, EFI_SYSTEM_TABLE * system_table)
     g_system_table = system_table;
 
     write_string(L"My first EFI loader\r\n");
-    if (EFI_ERROR(status))
-        return status;
 
     status = system_table->ConIn->Reset(system_table->ConIn, FALSE);
     if (EFI_ERROR(status))
@@ -45,12 +66,18 @@ efi_main(EFI_HANDLE image_handle, EFI_SYSTEM_TABLE * system_table)
             NULL,
             &buffer_size,
             buffer);
+    buffer_size /= sizeof(EFI_HANDLE);
     write_string(L"status = ");
     write_uint(status);
     write_string(L", num entries = ");
-    write_uint(buffer_size / sizeof(EFI_HANDLE));
+    write_uint(buffer_size);
     write_string(L"\r\n");
 
+    for (size_t i = 0u; i < buffer_size; i++)
+    {
+        check_handle(buffer[i]);
+    }
+
     write_string(L"Press any key...\r\n");
     while ((status = system_table->ConIn->ReadKeyStroke(system_table->ConIn, &key)) == EFI_NOT_READY)
     {