Messages in this thread Patch in this message | | | From | Deepak Gupta <> | Subject | [PATCH v2] scripts/gdb: add lx_current support for riscv | Date | Mon, 14 Nov 2022 17:29:17 -0800 |
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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.
Patch also adds new cached type "ulong" in scripts/gdb/linux/utils.py
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, + # then use scratch register + if (scratch_reg.cast(utils.get_ulong_type()) > current_tp.cast(utils.get_ulong_type())): + 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
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