Messages in this thread | | | Date | Tue, 15 Nov 2022 07:46:00 +0100 | From | Andrew Jones <> | Subject | Re: [PATCH v2] scripts/gdb: add lx_current support for riscv |
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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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