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

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Date:   Fri, 17 Feb 2023 19:11:52 -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 0/2] GDB: Support getting current task struct in UML

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:
-- 
2.30.2