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scripts/gdb: fix detection of current CPU in KGDB

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Directly read the current CPU number from the kgdb_active variable.

Before, the active CPU was obtained through the current task, which
required searching the task list for the pid of GDB's selected thread. 
Obtaining the pid was buggy: GDB may use selected_thread().ptid[1] (LWPID)
instead of .ptid[2] (TID) to store the threads pid; see
https://sourceware.org/gdb/current/onlinedocs/gdb.html/Threads-In-Python.html
As a result, the detection could return the wrong CPU number, leading to
incorrect results for $lx_per_cpu and $lx_current.

As a side effect, the patch significantly speeds up $lx_per_cpu and
$lx_current in KGDB by avoiding the task-list iteration.

Link: https://lkml.kernel.org/r/20240425153501.749966-5-mail@florommel.de
Signed-off-by: Florian Rommel <mail@florommel.de>
Cc: Andrew Jones <ajones@ventanamicro.com>
Cc: Deepak Gupta <debug@rivosinc.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Kieran Bingham <kbingham@kernel.org>
Cc: Kuan-Ying Lee <Kuan-Ying.Lee@mediatek.com>
Cc: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Florian Rommel 2024-04-25 17:35:01 +02:00 committed by Andrew Morton
parent 7566b063e9
commit 40eea5abbb
1 changed files with 1 additions and 5 deletions
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6
scripts/gdb/linux/cpus.py
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@ -26,11 +26,7 @@ def get_current_cpu():
if utils.get_gdbserver_type() == utils.GDBSERVER_QEMU:
return gdb.selected_thread().num - 1
elif utils.get_gdbserver_type() == utils.GDBSERVER_KGDB:
tid = gdb.selected_thread().ptid[2]
if tid > (0x100000000 - MAX_CPUS - 2):
return 0x100000000 - tid - 2
else:
return tasks.get_thread_info(tasks.get_task_by_pid(tid))['cpu']
return gdb.parse_and_eval("kgdb_active.counter")
else:
raise gdb.GdbError("Sorry, obtaining the current CPU is not yet "
"supported with this gdb server.")