linux-kernel - [PATCH v2 2/2] scripts/gdb: Support getting current task struct in UML

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Date:   Fri, 17 Feb 2023 19:11:54 -0600
From:   Glenn Washburn <development@...icientek.com>
To:     Jan Kiszka <jan.kiszka@...mens.com>,
        Kieran Bingham <kbingham@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Glenn Washburn <development@...icientek.com>,
        linux-um <linux-um@...ts.infradead.org>,
        Richard Weinberger <richard@....at>,
        Johannes Berg <johannes@...solutions.net>,
        Anton Ivanov <anton.ivanov@...-begemot.co.uk>
Subject: [PATCH v2 2/2] scripts/gdb: Support getting current task struct in UML

A running x86 UML kernel reports with architecture "i386:x86-64" as
it is a sub-architecture. However, a difference with bare-metal x86
kernels is in how it manages tasks and the current task struct. To
identify that the inferior is a UML kernel and not bare-metal, check
for the existence of the UML specific symbol "cpu_tasks" which
contains the current task struct.

Signed-off-by: Glenn Washburn <development@...icientek.com>
Reviewed-by: Jan Kiszka <jan.kiszka@...mens.com>
---
 scripts/gdb/linux/cpus.py | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/scripts/gdb/linux/cpus.py b/scripts/gdb/linux/cpus.py
index 3e02a1866751..4b4ce6464dee 100644
--- a/scripts/gdb/linux/cpus.py
+++ b/scripts/gdb/linux/cpus.py
@@ -163,8 +163,14 @@ def get_current_task(cpu):
     task_ptr_type = task_type.get_type().pointer()
 
     if utils.is_target_arch("x86"):
-        var_ptr = gdb.parse_and_eval("&current_task")
-        return per_cpu(var_ptr, cpu).dereference()
+        if gdb.lookup_global_symbol("cpu_tasks"):
+            # This is a UML kernel, which stores the current task
+            # differently than other x86 sub architectures
+            var_ptr = gdb.parse_and_eval("(struct task_struct *)cpu_tasks[0].task")
+            return var_ptr.dereference()
+        else:
+            var_ptr = gdb.parse_and_eval("&current_task")
+            return per_cpu(var_ptr, cpu).dereference()
     elif utils.is_target_arch("aarch64"):
         current_task_addr = gdb.parse_and_eval("$SP_EL0")
         if (current_task_addr >> 63) != 0:
-- 
2.30.2