Re: [PATCH v2 0/2] GDB: Support getting current task struct in UML

From: Jan Kiszka <jan.kiszka@siemens.com>
To: Glenn Washburn <development@efficientek.com>,
	Kieran Bingham <kbingham@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: linux-um <linux-um@lists.infradead.org>,
	Richard Weinberger <richard@nod.at>,
	Johannes Berg <johannes@sipsolutions.net>,
	Anton Ivanov <anton.ivanov@kot-begemot.co.uk>
Subject: Re: [PATCH v2 0/2] GDB: Support getting current task struct in UML
Date: Thu, 16 Feb 2023 08:51:52 +0100	[thread overview]
Message-ID: <8a22d84e-5cf4-bf41-220e-dc5e48fb2fc3@siemens.com> (raw)
In-Reply-To: <cover.1676532759.git.development@efficientek.com>

On 16.02.23 08:37, Glenn Washburn wrote:
> Added suggestions from Jan.
> 
> Glenn
> 
> Glenn Washburn (2):
>   scripts/gdb: Correct indentation in get_current_task
>   scripts/gdb: Support getting current task struct in UML
> 
>  scripts/gdb/linux/cpus.py | 24 +++++++++++++++---------
>  1 file changed, 15 insertions(+), 9 deletions(-)
> 
> Range-diff against v1:
> 1:  f33ebe524590 ! 1:  c5a916e094d9 scripts/gdb: Correct indentation in get_current_task
>     @@ Commit message
>      
>          There is an extra space in a couple blocks in get_current_task.
>          Though python does not care, let's make the spacing consistent.
>     +    Also, format better an if expression, removing unneeded parenthesis.
>      
>       ## scripts/gdb/linux/cpus.py ##
>      @@ scripts/gdb/linux/cpus.py: def get_current_task(cpu):
>     @@ scripts/gdb/linux/cpus.py: def get_current_task(cpu):
>      -             raise gdb.GdbError("Sorry, obtaining the current task is not allowed "
>      -                                "while running in userspace(EL0)")
>      +        current_task_addr = gdb.parse_and_eval("$SP_EL0")
>     -+        if((current_task_addr >> 63) != 0):
>     ++        if (current_task_addr >> 63) != 0:
>      +            current_task = current_task_addr.cast(task_ptr_type)
>      +            return current_task.dereference()
>      +        else:
> 2:  8c3db2291f58 ! 2:  683d10e752cd scripts/gdb: Support getting current task struct in UML
>     @@ Commit message
>          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, the
>     -    symbol "uml_kmalloc" is checked for. If it exists, then do the UML
>     -    specific way of getting the current task struct.
>     +    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.
>      
>       ## scripts/gdb/linux/cpus.py ##
>      @@ scripts/gdb/linux/cpus.py: def get_current_task(cpu):
>     @@ scripts/gdb/linux/cpus.py: 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()
>     -+        if gdb.lookup_global_symbol("uml_kmalloc"):
>     ++        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:
>     @@ scripts/gdb/linux/cpus.py: def get_current_task(cpu):
>      +            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):
>     +         if (current_task_addr >> 63) != 0:

Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>

Jan

-- 
Siemens AG, Technology
Competence Center Embedded Linux


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