gdb: add 'maintenance print record-instruction' command

While chasing some reverse debugging bugs, I found myself wondering what
was recorded by GDB to undo and redo a certain instruction. This commit
implements a simple way of printing that information.

If there isn't enough history to print the desired instruction (such as
when the user hasn't started recording yet or when they request 2
instructions back but only 1 was recorded), GDB warns the user like so:

(gdb) maint print record-instruction
Not enough recorded history

If there is enough, GDB prints the instruction like so:

(gdb) maint print record-instruction
4 bytes of memory at address 0x00007fffffffd5dc changed from: 01 00 00 00
Register eflags changed: [ IF ]
Register rip changed: (void (*)()) 0x401115 <main+15>

Approved-by: Eli Zaretskii <eliz@gnu.org>
Reviewed-by: Alexandra Hajkova <ahajkova@redhat.com>
Reviewed-by: Lancelot Six <lsix@lancelotsix.com>
Approved-by: Tom Tromey <tom@tromey.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/gdb/NEWS b/gdb/NEWS
index 41d8155..d8f4f39 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -9,6 +9,14 @@
   This support requires that GDB be built with Python scripting
   enabled.
 
+* New commands
+
+maintenance print record-instruction [ N ]
+  Print the recorded information for a given instruction.  If N is not given
+  prints how GDB would undo the last instruction executed.  If N is negative,
+  prints how GDB would undo the N-th previous instruction, and if N is
+  positive, it prints how GDB will redo the N-th following instruction.
+
 *** Changes in GDB 13
 
 * MI version 1 is deprecated, and will be removed in GDB 14.