Messages in this thread | | | From | Deepak Gupta <> | Date | Thu, 26 Oct 2023 16:41:13 -0700 | Subject | Re: [PATCH v5] scripts/gdb: add lx_current support for riscv |
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On Wed, Oct 4, 2023 at 10:29 PM Hsieh-Tseng Shen <woodrow.shen@sifive.com> wrote: > > On Mon, Jan 02, 2023 at 10:09:01AM +0100, Jan Kiszka wrote: > > 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 > > This patch had been pending for quite a while, and not sure if it's > still acceptable to be merged, but from my testing it's working fine > for me. Nevertheless, the v5 patch now has conflict with the current > master, so I've slightly modified for reference. It would be helpful > if Deepak can send v6 later on.
Thanks for testing it out. I just sent out a v6 based on v6.6-rc5.
-Deepak
> > Tested-by: Hsieh-Tseng Shen <woodrow.shen@sifive.com> > > v5 --> v6: > - dropped cache type "ulong" in scripts/gdb/linux/utils.py as it > already exists in the current 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..f8325cab5f1b 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") > -- > 2.31.1 > > Thank you
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