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)
Signed-off-by: Deepak Gupta <[email protected]>
Reviewed-by: Andrew Jones <[email protected]>
Reviewed-by: Palmer Dabbelt <[email protected]>
Acked-by: Palmer Dabbelt <[email protected]>
Tested-by: Hsieh-Tseng Shen <[email protected]>
---
Since patch has changed a little bit from v1 and I didn't include
changelog earlier, here it is.
v1 --> v2:
- added logic to locate task_struct irrespective of priv
- made locating task_struct agnostic to bitness(32 vs 64).
- added caching of ulong type in scripts/gdb/linux/utils.py
- added more descriptive commit message
v2 --> v3:
- amended commit message and source line to fit column width
v3 --> v4:
- amended commit message and remove whitespace in source
- added Reviewed-by for reviewers
v4 --> v5:
- changing the order of changelog and sign off/review tags in commit
v5 --> v6:
- rebased on 6.6-rc5. dropped changes in utils.py as they're upstream
---
scripts/gdb/linux/cpus.py | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/scripts/gdb/linux/cpus.py b/scripts/gdb/linux/cpus.py
index 255dc18cb9da..cba589e5b57d 100644
--- a/scripts/gdb/linux/cpus.py
+++ b/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")
--
2.42.0
Ping
+ CC: [email protected]
Who should I ping to make sure that it lands up in mainline?
It's quite a trivial change to support lx_current riscv arch.
-Deepak
On Thu, Oct 26, 2023 at 04:38:23PM -0700, 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_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)
>
>Signed-off-by: Deepak Gupta <[email protected]>
>Reviewed-by: Andrew Jones <[email protected]>
>Reviewed-by: Palmer Dabbelt <[email protected]>
>Acked-by: Palmer Dabbelt <[email protected]>
>Tested-by: Hsieh-Tseng Shen <[email protected]>
>
>---
>Since patch has changed a little bit from v1 and I didn't include
>changelog earlier, here it is.
>
>v1 --> v2:
> - added logic to locate task_struct irrespective of priv
> - made locating task_struct agnostic to bitness(32 vs 64).
> - added caching of ulong type in scripts/gdb/linux/utils.py
> - added more descriptive commit message
>
>v2 --> v3:
> - amended commit message and source line to fit column width
>
>v3 --> v4:
> - amended commit message and remove whitespace in source
> - added Reviewed-by for reviewers
>
>v4 --> v5:
> - changing the order of changelog and sign off/review tags in commit
>
>v5 --> v6:
> - rebased on 6.6-rc5. dropped changes in utils.py as they're upstream
>---
> scripts/gdb/linux/cpus.py | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
>diff --git a/scripts/gdb/linux/cpus.py b/scripts/gdb/linux/cpus.py
>index 255dc18cb9da..cba589e5b57d 100644
>--- a/scripts/gdb/linux/cpus.py
>+++ b/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")
>--
>2.42.0
>
On Thu, 2 Nov 2023 08:45:17 -0700 Deepak Gupta <[email protected]> wrote:
> Ping
>
> + CC: [email protected]
>
> Who should I ping to make sure that it lands up in mainline?
> It's quite a trivial change to support lx_current riscv arch.
I moved it from mm.git's mm-nonmm-unstable branch into the
mm-nonmm-stable branch earlier this week. mm-nonmm-stable is what I'll
be sending to Linus later this merge window.
On Thu, Nov 2, 2023 at 8:56 AM Andrew Morton <[email protected]> wrote:
>
> On Thu, 2 Nov 2023 08:45:17 -0700 Deepak Gupta <[email protected]> wrote:
>
> > Ping
> >
> > + CC: [email protected]
> >
> > Who should I ping to make sure that it lands up in mainline?
> > It's quite a trivial change to support lx_current riscv arch.
>
> I moved it from mm.git's mm-nonmm-unstable branch into the
> mm-nonmm-stable branch earlier this week. mm-nonmm-stable is what I'll
> be sending to Linus later this merge window.
>
Thanks