[PATCH v2] gdb: Add gdbinfo command for printing the load address of the EFI application

[Glenn Washburn <development@efficientek.com>]

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 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>
---
Range-diff against v1:
1:  1d438175061f ! 1:  24106a4ff806 gdb: Add gdbinfo command for printing the load address of the EFI application
    @@ grub-core/kern/efi/init.c: grub_addr_t grub_modbase;
           messages.  */
        grub_console_init ();
     @@ grub-core/kern/efi/init.c: grub_efi_init (void)
    - 	      0, 0, 0, NULL);
    +   grub_efi_system_table->boot_services->set_watchdog_timer (0, 0, 0, NULL);
      
        grub_efidisk_init ();
     +
    @@ include/grub/efi/debug.h (new)
     +#endif /* ! GRUB_EFI_DEBUG_HEADER */
     
      ## include/grub/efi/efi.h ##
    -@@ include/grub/efi/efi.h: grub_err_t grub_arch_efi_linux_boot_image(grub_addr_t addr, grub_size_t size,
    +@@ include/grub/efi/efi.h: grub_err_t grub_arch_efi_linux_load_image_header(grub_file_t file,
    + grub_err_t grub_arch_efi_linux_boot_image(grub_addr_t addr, grub_size_t size,
                                                 char *args);
    - #endif
      
     -grub_addr_t grub_efi_modules_addr (void);
     +grub_addr_t grub_efi_section_addr (const char *section);

 docs/grub.texi              | 13 ++++++++++++
 grub-core/Makefile.core.def |  1 +
 grub-core/kern/efi/debug.c  | 38 ++++++++++++++++++++++++++++++++++
 grub-core/kern/efi/efi.c    |  4 ++--
 grub-core/kern/efi/init.c   |  5 ++++-
 include/grub/efi/debug.h    | 41 +++++++++++++++++++++++++++++++++++++
 include/grub/efi/efi.h      |  2 +-
 7 files changed, 100 insertions(+), 4 deletions(-)
 create mode 100644 grub-core/kern/efi/debug.c
 create mode 100644 include/grub/efi/debug.h

diff --git a/docs/grub.texi b/docs/grub.texi
index 7ab1e0ab40ef..5fb074f66869 100644
--- a/docs/grub.texi
+++ b/docs/grub.texi
@@ -4301,6 +4301,7 @@ you forget a command, you can run the command @command{help}
 * export::                      Export an environment variable
 * false::                       Do nothing, unsuccessfully
 * fwsetup::                     Reboot into the firmware setup menu
+* gdbinfo::                     Provide info for debugging with GDB
 * gettext::                     Translate a string
 * gptsync::                     Fill an MBR based on GPT entries
 * halt::                        Shut down your computer
@@ -4833,6 +4834,18 @@ exit successfully if so.
 @end deffn
 
 
+@node gdbinfo
+@subsection gdbinfo
+
+@deffn Command gdbinfo
+Output text to be used as a GDB command for a GDB session using the gdb_grub
+script and attached to a running GRUB instance. The GDB command that is
+output will tell GDB how to load debugging symbols to their proper runtime
+address. Currently this is only available for EFI platforms. See the Debugging
+in the developer documentation for more information.
+@end deffn
+
+
 @node gettext
 @subsection gettext
 
diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
index 04549e868591..784f0a2136c2 100644
--- a/grub-core/Makefile.core.def
+++ b/grub-core/Makefile.core.def
@@ -211,6 +211,7 @@ kernel = {
 
   efi = disk/efi/efidisk.c;
   efi = kern/efi/efi.c;
+  efi = kern/efi/debug.c;
   efi = kern/efi/init.c;
   efi = kern/efi/mm.c;
   efi = term/efi/console.c;
diff --git a/grub-core/kern/efi/debug.c b/grub-core/kern/efi/debug.c
new file mode 100644
index 000000000000..506ad90dca06
--- /dev/null
+++ b/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_lockdown ("gdbinfo", grub_cmd_gdbinfo, 0,
+				  N_("Print infomation useful for GDB debugging"));
+}
diff --git a/grub-core/kern/efi/efi.c b/grub-core/kern/efi/efi.c
index 0e1ccf65ad2e..974fed8cb55c 100644
--- a/grub-core/kern/efi/efi.c
+++ b/grub-core/kern/efi/efi.c
@@ -303,7 +303,7 @@ grub_efi_get_variable (const char *var, const grub_efi_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;
@@ -332,7 +332,7 @@ 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;
     }
 
diff --git a/grub-core/kern/efi/init.c b/grub-core/kern/efi/init.c
index e873ef5298ff..ae8c2e1e499b 100644
--- a/grub-core/kern/efi/init.c
+++ b/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,
diff --git a/include/grub/efi/debug.h b/include/grub/efi/debug.h
new file mode 100644
index 000000000000..c2d2a03b06f1
--- /dev/null
+++ b/include/grub/efi/debug.h
@@ -0,0 +1,41 @@
+/*
+ *  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.h - declare variables and functions for EFI debugging support */
+
+#ifndef GRUB_EFI_DEBUG_HEADER
+#define GRUB_EFI_DEBUG_HEADER	1
+
+#include <grub/efi/efi.h>
+#include <grub/misc.h>
+
+
+void grub_efi_register_debug_commands (void);
+
+static inline void
+grub_efi_print_gdb_info (void)
+{
+  grub_addr_t text;
+
+  text = grub_efi_section_addr (".text");
+  if (!text)
+    return;
+
+  grub_printf ("dynamic_load_symbols %p\n", (void *)text);
+}
+
+#endif /* ! GRUB_EFI_DEBUG_HEADER */
diff --git a/include/grub/efi/efi.h b/include/grub/efi/efi.h
index 7071b8dc9783..5ec5af71eeb6 100644
--- a/include/grub/efi/efi.h
+++ b/include/grub/efi/efi.h
@@ -127,7 +127,7 @@ grub_err_t grub_arch_efi_linux_load_image_header(grub_file_t file,
 grub_err_t grub_arch_efi_linux_boot_image(grub_addr_t addr, grub_size_t size,
                                            char *args);
 
-grub_addr_t grub_efi_modules_addr (void);
+grub_addr_t grub_efi_section_addr (const char *section);
 
 void grub_efi_mm_init (void);
 void grub_efi_mm_fini (void);
-- 
2.34.1