The quilt patch titled
Subject: scripts/gdb: add lx_current support for riscv
has been removed from the -mm tree. Its filename was
scripts-gdb-add-lx_current-support-for-riscv.patch
This patch was dropped because it was merged into the mm-nonmm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Deepak Gupta <debug@xxxxxxxxxxxx>
Subject: scripts/gdb: add lx_current support for riscv
Date: Thu, 26 Oct 2023 16:38:23 -0700
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_sscratch CSR.
This patch assumes "tp" is pointing to task_struct. If value in
csr_sscratch is numerically greater than "tp" then it assumes csr_sscratch
is correct address of current task_struct. This logic holds when
- hart is in user space, "tp" will be less than csr_sscratch.
- hart is in kernel space but not in trap handler, "tp" will be more
than csr_sscratch (csr_sscratch being equal to 0).
- hart is executing trap handler
- "tp" is still pointing to user mode but csr_sscratch contains
ptr to task_struct. Thus numerically higher.
- "tp" is pointing to task_struct but csr_sscratch now contains
either 0 or numerically smaller value (transiently holds
user mode tp)
Link: https://lkml.kernel.org/r/20231026233837.612405-1-debug@xxxxxxxxxxxx
Signed-off-by: Deepak Gupta <debug@xxxxxxxxxxxx>
Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
Reviewed-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
Acked-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
Tested-by: Hsieh-Tseng Shen <woodrow.shen@xxxxxxxxxx>
Cc: Albert Ou <aou@xxxxxxxxxxxxxxxxx>
Cc: Glenn Washburn <development@xxxxxxxxxxxxxxx>
Cc: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Cc: Jeff Xie <xiehuan09@xxxxxxxxx>
Cc: Kieran Bingham <kbingham@xxxxxxxxxx>
Cc: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
Cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
scripts/gdb/linux/cpus.py | 15 +++++++++++++++
1 file changed, 15 insertions(+)
--- a/scripts/gdb/linux/cpus.py~scripts-gdb-add-lx_current-support-for-riscv
+++ a/scripts/gdb/linux/cpus.py
@@ -179,6 +179,21 @@ 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.
+ # and tp is used by user mode. So when scratch register holds larger value
+ # (negative address as ulong is larger 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")
_
Patches currently in -mm which might be from debug@xxxxxxxxxxxx are
