[PATCH 0/2] scripts/gdb: Fixes related to lx_per_cpu()

[PATCH 0/2] scripts/gdb: Fixes related to lx_per_cpu()

[Illia Ostapyshyn]

Hi all,

these patches (1) fix kgdb detection on systems featuring a single CPU and
(2) update the documentation to reflect the current usage of lx_per_cpu()
and update an outdated example of its usage.

Illia Ostapyshyn (2):
  scripts/gdb: Fix kgdb probing on single-core systems
  scripts/gdb: Update documentation for lx_per_cpu

 .../debugging/gdb-kernel-debugging.rst        | 34 ++++++++-----------
 .../zh_CN/dev-tools/gdb-kernel-debugging.rst  | 34 ++++++++-----------
 .../zh_TW/dev-tools/gdb-kernel-debugging.rst  | 34 ++++++++-----------
 scripts/gdb/linux/cpus.py                     |  4 +--
 scripts/gdb/linux/utils.py                    |  2 +-
 5 files changed, 48 insertions(+), 60 deletions(-)


base-commit: 95d3481af6dc90fd7175a7643fd108cdcb808ce5
-- 
2.47.2

[PATCH 1/2] scripts/gdb: Fix kgdb probing on single-core systems

[Illia Ostapyshyn]

When requested the list of threads via qfThreadInfo, gdb_cmd_query in
kernel/debug/gdbstub.c first returns "shadow" threads for CPUs followed
by the actual tasks in the system.  Extended qThreadExtraInfo queries
yield "shadowCPU%d" as the name for the CPU core threads.

This behavior is used by get_gdbserver_type() to probe for KGDB by
matching the name for the thread 2 against "shadowCPU".  This breaks
down on single-core systems, where thread 2 is the first nonshadow
thread.  Request the name for thread 1 instead.

As GDB assigns thread IDs in the order of their appearance, it is safe
to assume shadowCPU0 at ID 1 as long as CPU0 is not hotplugged.

Before:

(gdb) info threads
  Id   Target Id                      Frame
  1    Thread 4294967294 (shadowCPU0) kgdb_breakpoint ()
* 2    Thread 1 (swapper/0)           kgdb_breakpoint ()
  3    Thread 2 (kthreadd)            0x0000000000000000 in ?? ()
  ...
(gdb) p $lx_current().comm
Sorry, obtaining the current CPU is not yet supported with this gdb server.

After:

(gdb) info threads
  Id   Target Id                      Frame
  1    Thread 4294967294 (shadowCPU0) kgdb_breakpoint ()
* 2    Thread 1 (swapper/0)           kgdb_breakpoint ()
  3    Thread 2 (kthreadd)            0x0000000000000000 in ?? ()
  ...
(gdb) p $lx_current().comm
$1 = "swapper/0\000\000\000\000\000\000"

Signed-off-by: Illia Ostapyshyn <illia@yshyn.com>
---
 scripts/gdb/linux/utils.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/gdb/linux/utils.py b/scripts/gdb/linux/utils.py
index 03ebdccf5f69..877404e92dbb 100644
--- a/scripts/gdb/linux/utils.py
+++ b/scripts/gdb/linux/utils.py
@@ -200,7 +200,7 @@ def get_gdbserver_type():
 
     def probe_kgdb():
         try:
-            thread_info = gdb.execute("info thread 2", to_string=True)
+            thread_info = gdb.execute("info thread 1", to_string=True)
             return "shadowCPU" in thread_info
         except gdb.error:
             return False
-- 
2.47.2

[PATCH 2/2] scripts/gdb: Update documentation for lx_per_cpu

[Illia Ostapyshyn]

Commit db08c53fdd542bb7f83b ("scripts/gdb: fix parameter handling in
$lx_per_cpu") changed the parameter handling of lx_per_cpu to use
GdbValue instead of parsing the variable name.  Update the documentation
to reflect the new lx_per_cpu usage.  Update the hrtimer_bases example
to use rb_tree instead of the timerqueue_head.next pointer removed in
commit 511885d7061eda3eb1fa ("lib/timerqueue: Rely on rbtree semantics
for next timer").

Signed-off-by: Illia Ostapyshyn <illia@yshyn.com>
---
 .../debugging/gdb-kernel-debugging.rst        | 34 ++++++++-----------
 .../zh_CN/dev-tools/gdb-kernel-debugging.rst  | 34 ++++++++-----------
 .../zh_TW/dev-tools/gdb-kernel-debugging.rst  | 34 ++++++++-----------
 scripts/gdb/linux/cpus.py                     |  4 +--
 4 files changed, 47 insertions(+), 59 deletions(-)

diff --git a/Documentation/process/debugging/gdb-kernel-debugging.rst b/Documentation/process/debugging/gdb-kernel-debugging.rst
index 895285c037c7..9475c759c722 100644
--- a/Documentation/process/debugging/gdb-kernel-debugging.rst
+++ b/Documentation/process/debugging/gdb-kernel-debugging.rst
@@ -127,35 +127,31 @@ Examples of using the Linux-provided gdb helpers
 
 - Make use of the per-cpu function for the current or a specified CPU::
 
-    (gdb) p $lx_per_cpu("runqueues").nr_running
+    (gdb) p $lx_per_cpu(runqueues).nr_running
     $3 = 1
-    (gdb) p $lx_per_cpu("runqueues", 2).nr_running
+    (gdb) p $lx_per_cpu(runqueues, 2).nr_running
     $4 = 0
 
 - Dig into hrtimers using the container_of helper::
 
-    (gdb) set $next = $lx_per_cpu("hrtimer_bases").clock_base[0].active.next
-    (gdb) p *$container_of($next, "struct hrtimer", "node")
+    (gdb) set $leftmost = $lx_per_cpu(hrtimer_bases).clock_base[0].active.rb_root.rb_leftmost
+    (gdb) p *$container_of($leftmost, "struct hrtimer", "node")
     $5 = {
       node = {
         node = {
-          __rb_parent_color = 18446612133355256072,
-          rb_right = 0x0 <irq_stack_union>,
-          rb_left = 0x0 <irq_stack_union>
+          __rb_parent_color = 18446612686384860673,
+          rb_right = 0xffff888231da8b00,
+          rb_left = 0x0
         },
-        expires = {
-          tv64 = 1835268000000
-        }
+        expires = 1228461000000
       },
-      _softexpires = {
-        tv64 = 1835268000000
-      },
-      function = 0xffffffff81078232 <tick_sched_timer>,
-      base = 0xffff88003fd0d6f0,
-      state = 1,
-      start_pid = 0,
-      start_site = 0xffffffff81055c1f <hrtimer_start_range_ns+20>,
-      start_comm = "swapper/2\000\000\000\000\000\000"
+      _softexpires = 1228461000000,
+      function = 0xffffffff8137ab20 <tick_nohz_handler>,
+      base = 0xffff888231d9b4c0,
+      state = 1 '\001',
+      is_rel = 0 '\000',
+      is_soft = 0 '\000',
+      is_hard = 1 '\001'
     }
 
 
diff --git a/Documentation/translations/zh_CN/dev-tools/gdb-kernel-debugging.rst b/Documentation/translations/zh_CN/dev-tools/gdb-kernel-debugging.rst
index 3c133a918f30..282aacd33442 100644
--- a/Documentation/translations/zh_CN/dev-tools/gdb-kernel-debugging.rst
+++ b/Documentation/translations/zh_CN/dev-tools/gdb-kernel-debugging.rst
@@ -120,35 +120,31 @@ Kgdb内核调试器、QEMU等虚拟机管理程序或基于JTAG的硬件接口
 
 - 对当前或指定的CPU使用per-cpu函数::
 
-    (gdb) p $lx_per_cpu("runqueues").nr_running
+    (gdb) p $lx_per_cpu(runqueues).nr_running
     $3 = 1
-    (gdb) p $lx_per_cpu("runqueues", 2).nr_running
+    (gdb) p $lx_per_cpu(runqueues, 2).nr_running
     $4 = 0
 
 - 使用container_of查看更多hrtimers信息::
 
-    (gdb) set $next = $lx_per_cpu("hrtimer_bases").clock_base[0].active.next
-    (gdb) p *$container_of($next, "struct hrtimer", "node")
+    (gdb) set $leftmost = $lx_per_cpu(hrtimer_bases).clock_base[0].active.rb_root.rb_leftmost
+    (gdb) p *$container_of($leftmost, "struct hrtimer", "node")
     $5 = {
       node = {
         node = {
-          __rb_parent_color = 18446612133355256072,
-          rb_right = 0x0 <irq_stack_union>,
-          rb_left = 0x0 <irq_stack_union>
+          __rb_parent_color = 18446612686384860673,
+          rb_right = 0xffff888231da8b00,
+          rb_left = 0x0
         },
-        expires = {
-          tv64 = 1835268000000
-        }
+        expires = 1228461000000
       },
-      _softexpires = {
-        tv64 = 1835268000000
-      },
-      function = 0xffffffff81078232 <tick_sched_timer>,
-      base = 0xffff88003fd0d6f0,
-      state = 1,
-      start_pid = 0,
-      start_site = 0xffffffff81055c1f <hrtimer_start_range_ns+20>,
-      start_comm = "swapper/2\000\000\000\000\000\000"
+      _softexpires = 1228461000000,
+      function = 0xffffffff8137ab20 <tick_nohz_handler>,
+      base = 0xffff888231d9b4c0,
+      state = 1 '\001',
+      is_rel = 0 '\000',
+      is_soft = 0 '\000',
+      is_hard = 1 '\001'
     }
 
 
diff --git a/Documentation/translations/zh_TW/dev-tools/gdb-kernel-debugging.rst b/Documentation/translations/zh_TW/dev-tools/gdb-kernel-debugging.rst
index c881e8872b19..b595af59ba78 100644
--- a/Documentation/translations/zh_TW/dev-tools/gdb-kernel-debugging.rst
+++ b/Documentation/translations/zh_TW/dev-tools/gdb-kernel-debugging.rst
@@ -116,35 +116,31 @@ Kgdb內核調試器、QEMU等虛擬機管理程序或基於JTAG的硬件接口
 
 - 對當前或指定的CPU使用per-cpu函數::
 
-    (gdb) p $lx_per_cpu("runqueues").nr_running
+    (gdb) p $lx_per_cpu(runqueues).nr_running
     $3 = 1
-    (gdb) p $lx_per_cpu("runqueues", 2).nr_running
+    (gdb) p $lx_per_cpu(runqueues, 2).nr_running
     $4 = 0
 
 - 使用container_of查看更多hrtimers信息::
 
-    (gdb) set $next = $lx_per_cpu("hrtimer_bases").clock_base[0].active.next
-    (gdb) p *$container_of($next, "struct hrtimer", "node")
+    (gdb) set $leftmost = $lx_per_cpu(hrtimer_bases).clock_base[0].active.rb_root.rb_leftmost
+    (gdb) p *$container_of($leftmost, "struct hrtimer", "node")
     $5 = {
       node = {
         node = {
-          __rb_parent_color = 18446612133355256072,
-          rb_right = 0x0 <irq_stack_union>,
-          rb_left = 0x0 <irq_stack_union>
+          __rb_parent_color = 18446612686384860673,
+          rb_right = 0xffff888231da8b00,
+          rb_left = 0x0
         },
-        expires = {
-          tv64 = 1835268000000
-        }
+        expires = 1228461000000
       },
-      _softexpires = {
-        tv64 = 1835268000000
-      },
-      function = 0xffffffff81078232 <tick_sched_timer>,
-      base = 0xffff88003fd0d6f0,
-      state = 1,
-      start_pid = 0,
-      start_site = 0xffffffff81055c1f <hrtimer_start_range_ns+20>,
-      start_comm = "swapper/2\000\000\000\000\000\000"
+      _softexpires = 1228461000000,
+      function = 0xffffffff8137ab20 <tick_nohz_handler>,
+      base = 0xffff888231d9b4c0,
+      state = 1 '\001',
+      is_rel = 0 '\000',
+      is_soft = 0 '\000',
+      is_hard = 1 '\001'
     }
 
 
diff --git a/scripts/gdb/linux/cpus.py b/scripts/gdb/linux/cpus.py
index f506965ea759..6edf4ef61636 100644
--- a/scripts/gdb/linux/cpus.py
+++ b/scripts/gdb/linux/cpus.py
@@ -141,7 +141,7 @@ LxCpus()
 class PerCpu(gdb.Function):
     """Return per-cpu variable.
 
-$lx_per_cpu("VAR"[, CPU]): Return the per-cpu variable called VAR for the
+$lx_per_cpu(VAR[, CPU]): Return the per-cpu variable called VAR for the
 given CPU number. If CPU is omitted, the CPU of the current context is used.
 Note that VAR has to be quoted as string."""
 
@@ -158,7 +158,7 @@ PerCpu()
 class PerCpuPtr(gdb.Function):
     """Return per-cpu pointer.
 
-$lx_per_cpu_ptr("VAR"[, CPU]): Return the per-cpu pointer called VAR for the
+$lx_per_cpu_ptr(VAR[, CPU]): Return the per-cpu pointer called VAR for the
 given CPU number. If CPU is omitted, the CPU of the current context is used.
 Note that VAR has to be quoted as string."""
 
-- 
2.47.2