Messages in this thread Patch in this message | | | From | Deepak Gupta <> | Subject | [PATCH v6] scripts/gdb: add lx_current support for riscv | Date | Fri, 27 Oct 2023 21:58:00 -0700 |
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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_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 <debug@rivosinc.com> Reviewed-by: Andrew Jones <ajones@ventanamicro.com> Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com> Acked-by: Palmer Dabbelt <palmer@rivosinc.com> Tested-by: Hsieh-Tseng Shen <woodrow.shen@sifive.com>
--- 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
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