From dc9586823f3e06867344e6cf88741688c2c7737f Mon Sep 17 00:00:00 2001 From: Barry Song Date: Thu, 6 May 2021 18:05:06 -0700 Subject: scripts/gdb: document lx_current is only supported by x86 Patch series "scripts/gdb: clarify the platforms supporting lx_current and add arm64 support", v2. lx_current depends on per_cpu current_task variable which exists on x86 only. so it actually works on x86 only. the 1st patch documents this clearly; the 2nd patch adds support for arm64. This patch (of 2): 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 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. Link: https://lkml.kernel.org/r/20210314203444.15188-1-song.bao.hua@hisilicon.com Link: https://lkml.kernel.org/r/20210314203444.15188-2-song.bao.hua@hisilicon.com Signed-off-by: Barry Song Cc: Jan Kiszka Cc: Kieran Bingham Cc: Jonathan Corbet Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/dev-tools/gdb-kernel-debugging.rst | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation/dev-tools/gdb-kernel-debugging.rst') 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 -- cgit v1.2.3 From 526940e3962620f1a24d5e30c3dac7358194d963 Mon Sep 17 00:00:00 2001 From: Barry Song Date: Thu, 6 May 2021 18:05:09 -0700 Subject: scripts/gdb: add lx_current support for arm64 arm64 uses SP_EL0 to save the current task_struct address. While running in EL0, SP_EL0 is clobbered by userspace. So if the upper bit is not 1 (not TTBR1), the current address is invalid. This patch checks the upper bit of SP_EL0, if the upper bit is 1, lx_current() of arm64 will return the derefrence of current task. Otherwise, lx_current() will tell users they are running in userspace(EL0). While arm64 is running in EL0, it is actually pointless to print current task as the memory of kernel space is not accessible in EL0. Link: https://lkml.kernel.org/r/20210314203444.15188-3-song.bao.hua@hisilicon.com Signed-off-by: Barry Song Cc: Jan Kiszka Cc: Jonathan Corbet Cc: Kieran Bingham Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/dev-tools/gdb-kernel-debugging.rst | 2 +- scripts/gdb/linux/cpus.py | 13 +++++++++++++ 2 files changed, 14 insertions(+), 1 deletion(-) (limited to 'Documentation/dev-tools/gdb-kernel-debugging.rst') diff --git a/Documentation/dev-tools/gdb-kernel-debugging.rst b/Documentation/dev-tools/gdb-kernel-debugging.rst index 1586901b683c..8e0f1fe8d17a 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(supported by x86 only):: +- Examine fields of the current task struct(supported by x86 and arm64 only):: (gdb) p $lx_current().pid $1 = 4998 diff --git a/scripts/gdb/linux/cpus.py b/scripts/gdb/linux/cpus.py index f382762509d3..15fc4626d236 100644 --- a/scripts/gdb/linux/cpus.py +++ b/scripts/gdb/linux/cpus.py @@ -16,6 +16,9 @@ import gdb from linux import tasks, utils +task_type = utils.CachedType("struct task_struct") + + MAX_CPUS = 4096 @@ -157,9 +160,19 @@ Note that VAR has to be quoted as string.""" PerCpu() def get_current_task(cpu): + task_ptr_type = task_type.get_type().pointer() + if utils.is_target_arch("x86"): var_ptr = gdb.parse_and_eval("¤t_task") return per_cpu(var_ptr, cpu).dereference() + elif utils.is_target_arch("aarch64"): + current_task_addr = gdb.parse_and_eval("$SP_EL0") + if((current_task_addr >> 63) != 0): + current_task = current_task_addr.cast(task_ptr_type) + return current_task.dereference() + else: + raise gdb.GdbError("Sorry, obtaining the current task is not allowed " + "while running in userspace(EL0)") else: raise gdb.GdbError("Sorry, obtaining the current task is not yet " "supported with this arch") -- cgit v1.2.3