scripts/gdb/symbols: determine KASLR offset on s390

Use QEMU's qemu.PhyMemMode [1] functionality to read vmcore from the
physical memory the same way the existing dump tooling does this. 
Gracefully handle non-QEMU targets, early boot, and memory corruptions;
print a warning if such situation is detected.

[1] https://qemu-project.gitlab.io/qemu/system/gdb.html#examining-physical-memory

Link: https://lkml.kernel.org/r/20250303110437.79070-1-iii@linux.ibm.com
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Acked-by: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Andrew Donnellan <ajd@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Kieran Bingham <kbingham@kernel.org>
Cc: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 35 insertions, 0 deletions

diff --git a/scripts/gdb/linux/utils.py b/scripts/gdb/linux/utils.py
index 245ab297ea84..03ebdccf5f69 100644
--- a/scripts/gdb/linux/utils.py
+++ b/scripts/gdb/linux/utils.py
@@ -11,6 +11,11 @@
 # This work is licensed under the terms of the GNU GPL version 2.
 #
 
+import contextlib
+import dataclasses
+import re
+import typing
+
 import gdb
 
 
@@ -216,3 +221,33 @@ def gdb_eval_or_none(expresssion):
         return gdb.parse_and_eval(expresssion)
     except gdb.error:
         return None
+
+
+@contextlib.contextmanager
+def qemu_phy_mem_mode():
+    connection = gdb.selected_inferior().connection
+    orig = connection.send_packet("qqemu.PhyMemMode")
+    if orig not in b"01":
+        raise gdb.error("Unexpected qemu.PhyMemMode")
+    orig = orig.decode()
+    if connection.send_packet("Qqemu.PhyMemMode:1") != b"OK":
+        raise gdb.error("Failed to set qemu.PhyMemMode")
+    try:
+        yield
+    finally:
+        if connection.send_packet("Qqemu.PhyMemMode:" + orig) != b"OK":
+            raise gdb.error("Failed to restore qemu.PhyMemMode")
+
+
+@dataclasses.dataclass
+class VmCore:
+    kerneloffset: typing.Optional[int]
+
+
+def parse_vmcore(s):
+    match = re.search(r"KERNELOFFSET=([0-9a-f]+)", s)
+    if match is None:
+        kerneloffset = None
+    else:
+        kerneloffset = int(match.group(1), 16)
+    return VmCore(kerneloffset=kerneloffset)