The patch titled Subject: scripts/gdb: add lx_current support for riscv has been added to the -mm mm-nonmm-unstable branch. Its filename is scripts-gdb-add-lx_current-support-for-riscv.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/scripts-gdb-add-lx_current-support-for-riscv.patch This patch will later appear in the mm-nonmm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ 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 scripts-gdb-add-lx_current-support-for-riscv.patch