| Message ID | 20221115204003.1866421-1-debug@rivosinc.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v4] scripts/gdb: add lx_current support for riscv | expand |
| Context | Check | Description |
|---|---|---|
| conchuod/patch_count | success | Link |
| conchuod/cover_letter | success | Single patches do not need cover letters |
| conchuod/tree_selection | success | Guessed tree name to be for-next |
| conchuod/fixes_present | success | Fixes tag not required for -next series |
| conchuod/verify_signedoff | fail | author Signed-off-by missing |
| conchuod/kdoc | success | Errors and warnings before: 0 this patch: 0 |
| conchuod/module_param | success | Was 0 now: 0 |
| conchuod/build_rv32_defconfig | success | Build OK |
| conchuod/build_warn_rv64 | success | Errors and warnings before: 0 this patch: 0 |
| conchuod/dtb_warn_rv64 | success | Errors and warnings before: 0 this patch: 0 |
| conchuod/header_inline | success | No static functions without inline keyword in header files |
| conchuod/checkpatch | success | total: 0 errors, 0 warnings, 0 checks, 38 lines checked |
| conchuod/source_inline | success | Was 0 now: 0 |
| conchuod/build_rv64_nommu_k210_defconfig | success | Build OK |
| conchuod/verify_fixes | success | No Fixes tag |
| conchuod/build_rv64_nommu_virt_defconfig | success | Build OK |
Hey Deepak, On 15/11/2022 20:40, Deepak Gupta wrote: > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe > > 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 > > Since patch has changed a little bit from v1 and I didn't include > changelog earlier, here it is. This bit here needs to go below the --- line as it should not end up in the commit logs (as everything below the --- is ignored. > > --- > 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 > --- > > Signed-off-by: Deepak Gupta <debug@rivosinc.com> > Reviewed-by: Andrew Jones <ajones@ventanamicro.com> And this bit needs to go above the first --- line as it does need to go into the commit logs. The order is: $subject body tags --- changelog & comments diffs For example, this is what I see when I apply the patch: $ b4 shazam 20221115204003.1866421-1-debug@rivosinc.com Grabbing thread from lore.kernel.org/all/20221115204003.1866421-1-debug%40rivosinc.com/t.mbox.gz Checking for newer revisions on https://lore.kernel.org/all/ Analyzing 13 messages in the thread Will use the latest revision: v4 You can pick other revisions using the -vN flag Checking attestation on all messages, may take a moment... --- ✓ [PATCH v4] scripts/gdb: add lx_current support for riscv --- ✓ Signed: DKIM/rivosinc-com.20210112.gappssmtp.com (From: debug@rivosinc.com) --- Total patches: 1 --- Applying: scripts/gdb: add lx_current support for riscv $ git show commit 5c93617c68980f767e312fc51849d78093f56e72 (HEAD) Author: Deepak Gupta <debug@rivosinc.com> Date: Tue Nov 15 12:40:03 2022 -0800 scripts/gdb: add lx_current support for riscv 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 Since patch has changed a little bit from v1 and I didn't include changelog earlier, here it is. Taken a wee bit of the back and forth, Looks like you're nearly there though! Conor.
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) + + 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)
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 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 --- Signed-off-by: Deepak Gupta <debug@rivosinc.com> Reviewed-by: Andrew Jones <ajones@ventanamicro.com> --- scripts/gdb/linux/cpus.py | 15 +++++++++++++++ scripts/gdb/linux/utils.py | 5 +++++ 2 files changed, 20 insertions(+)