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Subject[PATCH v2 1/2] scripts/gdb: document lx_current is only supported by x86
Date
x86 is the only architecture which has per_cpu current_task:
arch$ git grep current_task | grep -i per_cpu
x86/include/asm/current.h:DECLARE_PER_CPU(struct task_struct *, current_task);
x86/kernel/cpu/common.c:DEFINE_PER_CPU(struct task_struct *, current_task) ____cacheline_aligned =
x86/kernel/cpu/common.c:EXPORT_PER_CPU_SYMBOL(current_task);
x86/kernel/cpu/common.c:DEFINE_PER_CPU(struct task_struct *, current_task) = &init_task;
x86/kernel/cpu/common.c:EXPORT_PER_CPU_SYMBOL(current_task);
x86/kernel/smpboot.c: per_cpu(current_task, cpu) = idle;

On other architectures, lx_current() will lead to a python exception:
(gdb) p $lx_current().pid
Python Exception <class 'gdb.error'> No symbol "current_task" in current context.:
Error occurred in Python: No symbol "current_task" in current context.

To avoid more people struggling and wasting time in other architectures,
document it.

Cc: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
---
Documentation/dev-tools/gdb-kernel-debugging.rst | 2 +-
scripts/gdb/linux/cpus.py | 10 ++++++++--
2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/Documentation/dev-tools/gdb-kernel-debugging.rst b/Documentation/dev-tools/gdb-kernel-debugging.rst
index 4756f6b3a04e..1586901b683c 100644
--- a/Documentation/dev-tools/gdb-kernel-debugging.rst
+++ b/Documentation/dev-tools/gdb-kernel-debugging.rst
@@ -114,7 +114,7 @@ Examples of using the Linux-provided gdb helpers
[ 0.000000] BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
....

-- Examine fields of the current task struct::
+- Examine fields of the current task struct(supported by x86 only)::

(gdb) p $lx_current().pid
$1 = 4998
diff --git a/scripts/gdb/linux/cpus.py b/scripts/gdb/linux/cpus.py
index 008e62f3190d..f382762509d3 100644
--- a/scripts/gdb/linux/cpus.py
+++ b/scripts/gdb/linux/cpus.py
@@ -156,6 +156,13 @@ Note that VAR has to be quoted as string."""

PerCpu()

+def get_current_task(cpu):
+ if utils.is_target_arch("x86"):
+ var_ptr = gdb.parse_and_eval("&current_task")
+ return per_cpu(var_ptr, cpu).dereference()
+ else:
+ raise gdb.GdbError("Sorry, obtaining the current task is not yet "
+ "supported with this arch")

class LxCurrentFunc(gdb.Function):
"""Return current task.
@@ -167,8 +174,7 @@ number. If CPU is omitted, the CPU of the current context is used."""
super(LxCurrentFunc, self).__init__("lx_current")

def invoke(self, cpu=-1):
- var_ptr = gdb.parse_and_eval("&current_task")
- return per_cpu(var_ptr, cpu).dereference()
+ return get_current_task(cpu)


LxCurrentFunc()
--
2.25.1
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