gdb: Add gdbinfo command for printing the load address of the EFI application

EFI firmware determines where to load the GRUB EFI at runtime, and so the
addresses of debug symbols are not known ahead of time. There is a command
defined in the gdb_grub script which will load the debug symbols at the
appropriate addresses, if given the application load address for GRUB.
So add a command named "gdbinfo" to allow the user to print this GDB command
string with the application load address on-demand. For the outputted GDB
command to have any effect when entered into a GDB session, GDB should have
been started with the script as an argument to the -x option or sourced into
an active GDB session before running the outputted command.

Documentation for the gdbinfo command is also added.

Co-developed-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/kern/efi/debug.c

@@ -0,0 +1,38 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2022  Free Software Foundation, Inc.
+ *
+ *  GRUB is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  GRUB is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ */
+/* debug.c - aides for debugging the EFI application */
+
+#include <grub/efi/debug.h>
+#include <grub/command.h>
+#include <grub/i18n.h>
+
+static grub_err_t
+grub_cmd_gdbinfo (struct grub_command *cmd __attribute__ ((unused)),
+		  int argc __attribute__ ((unused)),
+		  char **args __attribute__ ((unused)))
+{
+  grub_efi_print_gdb_info ();
+  return 0;
+}
+
+void
+grub_efi_register_debug_commands (void)
+{
+  grub_register_command ("gdbinfo", grub_cmd_gdbinfo, 0,
+			 N_("Print infomation useful for GDB debugging"));
+}

grub-core/kern/efi/efi.c

@@ -320,7 +320,7 @@ grub_efi_get_variable (const char *var, const grub_guid_t *guid,
 /* Search the mods section from the PE32/PE32+ image. This code uses
    a PE32 header, but should work with PE32+ as well.  */
 grub_addr_t
-grub_efi_modules_addr (void)
+grub_efi_section_addr (const char *section_name)
 {
   grub_efi_loaded_image_t *image;
   struct grub_msdos_image_header *header;
@@ -349,7 +349,7 @@ grub_efi_modules_addr (void)
        i < coff_header->num_sections;
        i++, section++)
     {
-      if (grub_strcmp (section->name, "mods") == 0)
+      if (grub_strcmp (section->name, section_name) == 0)
 	break;
     }
 

grub-core/kern/efi/init.c

@@ -19,6 +19,7 @@
 
 #include <grub/efi/efi.h>
 #include <grub/efi/console.h>
+#include <grub/efi/debug.h>
 #include <grub/efi/disk.h>
 #include <grub/efi/sb.h>
 #include <grub/lockdown.h>
@@ -104,7 +105,7 @@ grub_addr_t grub_modbase;
 void
 grub_efi_init (void)
 {
-  grub_modbase = grub_efi_modules_addr ();
+  grub_modbase = grub_efi_section_addr ("mods");
   /* First of all, initialize the console so that GRUB can display
      messages.  */
   grub_console_init ();
@@ -127,6 +128,8 @@ grub_efi_init (void)
   grub_efi_system_table->boot_services->set_watchdog_timer (0, 0, 0, NULL);
 
   grub_efidisk_init ();
+
+  grub_efi_register_debug_commands ();
 }
 
 void (*grub_efi_net_config) (grub_efi_handle_t hnd,