[PATCH 3/3] kgdb: Add command linux.vmcoreinfo to kgdb

[Amal Raj T <tjarlama@gmail.com>]

From: Amal Raj T <amalrajt@meta.com>

Add a new query `linux.vmcoreinfo` to kgdb that returns
vmcoreinfo to the client using the mem2ebin encoding.
Maximum size of output buffer is set to 3X the maximum
size of VMCOREINFO_BYTES (kgdb_mem2ebin() requires 1x
for the temporary copy plus up to 2x for the escaped
data).

Signed-off-by: Amal Raj T <amalrajt@meta.com>
---
 kernel/debug/gdbstub.c | 10 +++++++++-
 lib/Kconfig.kgdb       |  1 +
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/debug/gdbstub.c b/kernel/debug/gdbstub.c
index 6198d2eb49c4..5bec444fc6d3 100644
--- a/kernel/debug/gdbstub.c
+++ b/kernel/debug/gdbstub.c
@@ -34,13 +34,14 @@
 #include <linux/uaccess.h>
 #include <asm/cacheflush.h>
 #include <linux/unaligned.h>
+#include <linux/vmcore_info.h>
 #include "debug_core.h"
 
 #define KGDB_MAX_THREAD_QUERY 17
 
 /* Our I/O buffers. */
 static char			remcom_in_buffer[BUFMAX];
-static char			remcom_out_buffer[BUFMAX];
+static char			remcom_out_buffer[MAX(VMCOREINFO_BYTES*3, BUFMAX)];
 static int			gdbstub_use_prev_in_buf;
 static int			gdbstub_prev_in_buf_pos;
 
@@ -768,6 +769,13 @@ static void gdb_cmd_query(struct kgdb_state *ks)
 		*(--ptr) = '\0';
 		break;
 
+	case 'l':
+		if (memcmp(remcom_in_buffer + 1, "linux.vmcoreinfo", 16) == 0) {
+			remcom_out_buffer[0] = 'Q';
+			kgdb_mem2ebin(vmcoreinfo_data, remcom_out_buffer + 1, vmcoreinfo_size);
+		}
+		break;
+
 	case 'C':
 		/* Current thread id */
 		strcpy(remcom_out_buffer, "QC");
diff --git a/lib/Kconfig.kgdb b/lib/Kconfig.kgdb
index 537e1b3f5734..012529eee79e 100644
--- a/lib/Kconfig.kgdb
+++ b/lib/Kconfig.kgdb
@@ -12,6 +12,7 @@ menuconfig KGDB
 	bool "KGDB: kernel debugger"
 	depends on HAVE_ARCH_KGDB
 	depends on DEBUG_KERNEL
+	select VMCORE_INFO
 	help
 	  If you say Y here, it will be possible to remotely debug the
 	  kernel using gdb.  It is recommended but not required, that
-- 
2.43.5