[PATCH v4 12/15] gdb: Allow running user-defined commands at GRUB start

[Glenn Washburn <development@efficientek.com>]

A new command, run_on_start, is created which handles some complexities
of the EFI platform when breaking on GRUB start. If GRUB start is hooked,
run "onstart" command if it is defned.

Signed-off-by: Glenn Washburn <development@efficientek.com>
---
 grub-core/gdb_grub.in | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/grub-core/gdb_grub.in b/grub-core/gdb_grub.in
index 8ae6344edf..3b3cea1a4d 100644
--- a/grub-core/gdb_grub.in
+++ b/grub-core/gdb_grub.in
@@ -36,6 +36,8 @@ end
 define dynamic_load_symbols
 	dynamic_load_kernel_exec_symbols $arg0
 
+	run_on_start
+
 	# We may have been very late to loading the kernel.exec symbols and
 	# and modules may already be loaded. So load symbols for any already
 	# loaded.
@@ -134,6 +136,41 @@ document runtime_load_module
 	Load module symbols at runtime as they are loaded.
 end
 
+define run_on_start
+	# TODO: Add check to see if _start symbol is defined, if not, then
+	# the symbols have not yet been loaded and this command will not work.
+	watch *_start
+	set $break_efi_start_bpnum = $bpnum
+	commands
+		silent
+		delete $break_efi_start_bpnum
+		break _start
+		commands
+			silent
+			delete $break_efi_start_bpnum
+			set $onstart_name = "onstart"
+			is_user_command $onstart_name
+			if $ret
+				onstart
+			end
+			continue
+		end
+		set $break_efi_start_bpnum = $bpnum
+		continue
+	end
+end
+document run_on_start
+	On some targets, such as x86_64-efi, even if you know where the
+	firmware will load the grub image, you can not simply set a break
+	point before the image is loaded because loading the image
+	overwrites the break point in memory. So setup a hardware watch
+	point, which does not have that problem, and if that gets triggered,
+	then reset the break point. If a user-defined command named
+	"onstart" exists it will be run after the start is hit.
+	NOTE: This assumes symbols have already been correctly loaded for
+	the EFI application.
+end
+
 ###
 
 set confirm off
@@ -151,6 +188,7 @@ if ! $runonce
 		exec-file kernel.exec
 	else
 		file kernel.exec
+		run_on_start
 		runtime_load_module
 	end
 
-- 
2.34.1