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    SubjectRe: [PATCH v2] scripts/gdb: add lx_current support for riscv
    On Mon, Nov 14, 2022 at 05:29:17PM -0800, Deepak Gupta wrote:
    > csr_sscratch CSR holds current task_struct address when hart is in user space.
    > trap handler on entry spills csr_sscratch into "tp" (x2) register and zeroes out
    > csr_sscratch CSR. trap handler on exit reloads "tp" with expected user mode value
    > and place current task_struct address again in csr_scratch CSR.
    >
    > This patch assumes "tp" is pointing to task_struct. If value in csr_scratch is numerically
    > greater than "tp" then it assumes csr_scratch is correct address of current task_struct.
    > This logic holds when
    > - hart is in user space, "tp" will be less than csr_scratch.
    > - hart is in kernel space but not in trap handler, "tp" will be more than csr_scratch.
    > - hart is executing trap handler
    > - "tp" is still pointing to user mode but csr_scratch contains ptr to task_struct.
    > numerically higher.
    > - "tp" is now pointing to task_struct but csr_scratch now contains either 0 or numerically
    > smaller value.

    When is (csr_scratch != 0 && csr_scratch < tp)? IIUC, it should always be
    zero or >= tp.

    >
    > Patch also adds new cached type "ulong" in scripts/gdb/linux/utils.py

    Please wrap commit message lines at ~74.

    >
    > Signed-off-by: Deepak Gupta <debug@rivosinc.com>
    > ---
    > scripts/gdb/linux/cpus.py | 15 +++++++++++++++
    > scripts/gdb/linux/utils.py | 5 +++++
    > 2 files changed, 20 insertions(+)
    >
    > diff --git a/scripts/gdb/linux/cpus.py b/scripts/gdb/linux/cpus.py
    > index 15fc4626d236..fd818d7896ce 100644
    > --- a/scripts/gdb/linux/cpus.py
    > +++ b/scripts/gdb/linux/cpus.py
    > @@ -173,6 +173,21 @@ def get_current_task(cpu):
    > else:
    > raise gdb.GdbError("Sorry, obtaining the current task is not allowed "
    > "while running in userspace(EL0)")
    > + elif utils.is_target_arch("riscv"):
    > + current_tp = gdb.parse_and_eval("$tp")
    > + scratch_reg = gdb.parse_and_eval("$sscratch")
    > +
    > + # by default tp points to current task
    > + current_task = current_tp.cast(task_ptr_type)
    > +
    > + # scratch register is set 0 in trap handler after entering kernel.
    > + # When hart is in user mode, scratch register is pointing to task_struct.
    > + # So when scratch register holds higher value (negative address as ulong is bigger value) than tp,

    Please wrap source lines at 100.

    > + # then use scratch register
    > + if (scratch_reg.cast(utils.get_ulong_type()) > current_tp.cast(utils.get_ulong_type())):
    ^ extra space here

    > + current_task = scratch_reg.cast(task_ptr_type)
    > +
    > + return current_task.dereference()
    > else:
    > raise gdb.GdbError("Sorry, obtaining the current task is not yet "
    > "supported with this arch")
    > diff --git a/scripts/gdb/linux/utils.py b/scripts/gdb/linux/utils.py
    > index 1553f68716cc..ddaf3089170d 100644
    > --- a/scripts/gdb/linux/utils.py
    > +++ b/scripts/gdb/linux/utils.py
    > @@ -35,12 +35,17 @@ class CachedType:
    >
    >
    > long_type = CachedType("long")
    > +ulong_type = CachedType("ulong")
    > atomic_long_type = CachedType("atomic_long_t")
    >
    > def get_long_type():
    > global long_type
    > return long_type.get_type()
    >
    > +def get_ulong_type():
    > + global ulong_type
    > + return ulong_type.get_type()
    > +
    > def offset_of(typeobj, field):
    > element = gdb.Value(0).cast(typeobj)
    > return int(str(element[field].address).split()[0], 16)
    > --
    > 2.25.1
    >

    Besides the line wrapping and the commit message clarification this looks
    good to me.

    Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

    Thanks,
    drew

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