Messages in this thread | | | Date | Mon, 2 Jan 2023 10:09:01 +0100 | Subject | Re: [PATCH v5] scripts/gdb: add lx_current support for riscv | From | Jan Kiszka <> |
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On 15.11.22 23:10, 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) > > Patch also adds new cached type "ulong" in scripts/gdb/linux/utils.py > > Signed-off-by: Deepak Gupta <debug@rivosinc.com> > Reviewed-by: Andrew Jones <ajones@ventanamicro.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 > --- > --- > 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..14c22f82449b 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. > + # 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)
Why not if-else for the assignment here?
> + > + 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)
Looks good to me otherwise.
Jan
-- Siemens AG, Technology Competence Center Embedded Linux
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