scripts/gdb: update for lockless printk ringbuffer

With the introduction of the lockless printk ringbuffer, the data
structure for the kernel log buffer was changed. Update the gdb
scripts to be able to parse/print the new log buffer structure.

Fixes: 896fbe20b4e2333fb55 ("printk: use the lockless ringbuffer")
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Petr Mladek <pmladek@suse.com>
[akpm@linux-foundation.org: A typo fix.]
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200814212525.6118-3-john.ogness@linutronix.de

2 files changed, 209 insertions, 83 deletions

diff --git a/Documentation/admin-guide/kdump/gdbmacros.txt b/Documentation/admin-guide/kdump/gdbmacros.txt
index 220d0a80ca2c..7adece30237e 100644
--- a/Documentation/admin-guide/kdump/gdbmacros.txt
+++ b/Documentation/admin-guide/kdump/gdbmacros.txt
@@ -170,57 +170,111 @@ document trapinfo
 	address the kernel panicked.
 end
 
-define dump_log_idx
-	set $idx = $arg0
+define dump_record
+	set var $desc = $arg0
 	if ($argc > 1)
-		set $prev_flags = $arg1
+		set var $prev_flags = $arg1
 	else
-		set $prev_flags = 0
+		set var $prev_flags = 0
 	end
-	set $msg = ((struct printk_log *) (log_buf + $idx))
-	set $prefix = 1
-	set $newline = 1
-	set $log = log_buf + $idx + sizeof(*$msg)
-
-	# prev & LOG_CONT && !(msg->flags & LOG_PREIX)
-	if (($prev_flags & 8) && !($msg->flags & 4))
-		set $prefix = 0
+
+	set var $info = &$desc->info
+	set var $prefix = 1
+	set var $newline = 1
+
+	set var $begin = $desc->text_blk_lpos.begin % (1U << prb->text_data_ring.size_bits)
+	set var $next = $desc->text_blk_lpos.next % (1U << prb->text_data_ring.size_bits)
+
+	# handle data-less record
+	if ($begin & 1)
+		set var $text_len = 0
+		set var $log = ""
+	else
+		# handle wrapping data block
+		if ($begin > $next)
+			set var $begin = 0
+		end
+
+		# skip over descriptor id
+		set var $begin = $begin + sizeof(long)
+
+		# handle truncated message
+		if ($next - $begin < $info->text_len)
+			set var $text_len = $next - $begin
+		else
+			set var $text_len = $info->text_len
+		end
+
+		set var $log = &prb->text_data_ring.data[$begin]
+	end
+
+	# prev & LOG_CONT && !(info->flags & LOG_PREIX)
+	if (($prev_flags & 8) && !($info->flags & 4))
+		set var $prefix = 0
 	end
 
-	# msg->flags & LOG_CONT
-	if ($msg->flags & 8)
+	# info->flags & LOG_CONT
+	if ($info->flags & 8)
 		# (prev & LOG_CONT && !(prev & LOG_NEWLINE))
 		if (($prev_flags & 8) && !($prev_flags & 2))
-			set $prefix = 0
+			set var $prefix = 0
 		end
-		# (!(msg->flags & LOG_NEWLINE))
-		if (!($msg->flags & 2))
-			set $newline = 0
+		# (!(info->flags & LOG_NEWLINE))
+		if (!($info->flags & 2))
+			set var $newline = 0
 		end
 	end
 
 	if ($prefix)
-		printf "[%5lu.%06lu] ", $msg->ts_nsec / 1000000000, $msg->ts_nsec % 1000000000
+		printf "[%5lu.%06lu] ", $info->ts_nsec / 1000000000, $info->ts_nsec % 1000000000
 	end
-	if ($msg->text_len != 0)
-		eval "printf \"%%%d.%ds\", $log", $msg->text_len, $msg->text_len
+	if ($text_len)
+		eval "printf \"%%%d.%ds\", $log", $text_len, $text_len
 	end
 	if ($newline)
 		printf "\n"
 	end
-	if ($msg->dict_len > 0)
-		set $dict = $log + $msg->text_len
-		set $idx = 0
-		set $line = 1
-		while ($idx < $msg->dict_len)
+
+	# handle dictionary data
+
+	set var $begin = $desc->dict_blk_lpos.begin % (1U << prb->dict_data_ring.size_bits)
+	set var $next = $desc->dict_blk_lpos.next % (1U << prb->dict_data_ring.size_bits)
+
+	# handle data-less record
+	if ($begin & 1)
+		set var $dict_len = 0
+		set var $dict = ""
+	else
+		# handle wrapping data block
+		if ($begin > $next)
+			set var $begin = 0
+		end
+
+		# skip over descriptor id
+		set var $begin = $begin + sizeof(long)
+
+		# handle truncated message
+		if ($next - $begin < $info->dict_len)
+			set var $dict_len = $next - $begin
+		else
+			set var $dict_len = $info->dict_len
+		end
+
+		set var $dict = &prb->dict_data_ring.data[$begin]
+	end
+
+	if ($dict_len > 0)
+		set var $idx = 0
+		set var $line = 1
+		while ($idx < $dict_len)
 			if ($line)
 				printf " "
-				set $line = 0
+				set var $line = 0
 			end
-			set $c = $dict[$idx]
+			set var $c = $dict[$idx]
 			if ($c == '\0')
 				printf "\n"
-				set $line = 1
+				set var $line = 1
 			else
 				if ($c < ' ' || $c >= 127 || $c == '\\')
 					printf "\\x%02x", $c
@@ -228,33 +282,40 @@ define dump_log_idx
 					printf "%c", $c
 				end
 			end
-			set $idx = $idx + 1
+			set var $idx = $idx + 1
 		end
 		printf "\n"
 	end
 end
-document dump_log_idx
-	Dump a single log given its index in the log buffer.  The first
-	parameter is the index into log_buf, the second is optional and
-	specified the previous log buffer's flags, used for properly
-	formatting continued lines.
+document dump_record
+	Dump a single record. The first parameter is the descriptor
+	sequence number, the second is optional and specifies the
+	previous record's flags, used for properly formatting
+	continued lines.
 end
 
 define dmesg
-	set $i = log_first_idx
-	set $end_idx = log_first_idx
-	set $prev_flags = 0
+	set var $desc_committed = 1UL << ((sizeof(long) * 8) - 1)
+	set var $flags_mask = 3UL << ((sizeof(long) * 8) - 2)
+	set var $id_mask = ~$flags_mask
+
+	set var $desc_count = 1U << prb->desc_ring.count_bits
+	set var $prev_flags = 0
+
+	set var $id = prb->desc_ring.tail_id.counter
+	set var $end_id = prb->desc_ring.head_id.counter
 
 	while (1)
-		set $msg = ((struct printk_log *) (log_buf + $i))
-		if ($msg->len == 0)
-			set $i = 0
-		else
-			dump_log_idx $i $prev_flags
-			set $i = $i + $msg->len
-			set $prev_flags = $msg->flags
+		set var $desc = &prb->desc_ring.descs[$id % $desc_count]
+
+		# skip non-committed record
+		if (($desc->state_var.counter & $flags_mask) == $desc_committed)
+			dump_record $desc $prev_flags
+			set var $prev_flags = $desc->info.flags
 		end
-		if ($i == $end_idx)
+
+		set var $id = ($id + 1) & $id_mask
+		if ($id == $end_id)
 			loop_break
 		end
 	end
diff --git a/scripts/gdb/linux/dmesg.py b/scripts/gdb/linux/dmesg.py
index 2fa7bb83885f..6c6022012ea8 100644
--- a/scripts/gdb/linux/dmesg.py
+++ b/scripts/gdb/linux/dmesg.py
@@ -16,8 +16,13 @@ import sys
 
 from linux import utils
 
-printk_log_type = utils.CachedType("struct printk_log")
-
+printk_info_type = utils.CachedType("struct printk_info")
+prb_data_blk_lpos_type = utils.CachedType("struct prb_data_blk_lpos")
+prb_desc_type = utils.CachedType("struct prb_desc")
+prb_desc_ring_type = utils.CachedType("struct prb_desc_ring")
+prb_data_ring_type = utils.CachedType("struct prb_data_ring")
+printk_ringbuffer_type = utils.CachedType("struct printk_ringbuffer")
+atomic_long_type = utils.CachedType("atomic_long_t")
 
 class LxDmesg(gdb.Command):
     """Print Linux kernel log buffer."""
@@ -26,44 +31,102 @@ class LxDmesg(gdb.Command):
         super(LxDmesg, self).__init__("lx-dmesg", gdb.COMMAND_DATA)
 
     def invoke(self, arg, from_tty):
-        log_buf_addr = int(str(gdb.parse_and_eval(
-            "(void *)'printk.c'::log_buf")).split()[0], 16)
-        log_first_idx = int(gdb.parse_and_eval("'printk.c'::log_first_idx"))
-        log_next_idx = int(gdb.parse_and_eval("'printk.c'::log_next_idx"))
-        log_buf_len = int(gdb.parse_and_eval("'printk.c'::log_buf_len"))
-
         inf = gdb.inferiors()[0]
-        start = log_buf_addr + log_first_idx
-        if log_first_idx < log_next_idx:
-            log_buf_2nd_half = -1
-            length = log_next_idx - log_first_idx
-            log_buf = utils.read_memoryview(inf, start, length).tobytes()
-        else:
-            log_buf_2nd_half = log_buf_len - log_first_idx
-            a = utils.read_memoryview(inf, start, log_buf_2nd_half)
-            b = utils.read_memoryview(inf, log_buf_addr, log_next_idx)
-            log_buf = a.tobytes() + b.tobytes()
-
-        length_offset = printk_log_type.get_type()['len'].bitpos // 8
-        text_len_offset = printk_log_type.get_type()['text_len'].bitpos // 8
-        time_stamp_offset = printk_log_type.get_type()['ts_nsec'].bitpos // 8
-        text_offset = printk_log_type.get_type().sizeof
-
-        pos = 0
-        while pos < log_buf.__len__():
-            length = utils.read_u16(log_buf, pos + length_offset)
-            if length == 0:
-                if log_buf_2nd_half == -1:
-                    gdb.write("Corrupted log buffer!\n")
+
+        # read in prb structure
+        prb_addr = int(str(gdb.parse_and_eval("(void *)'printk.c'::prb")).split()[0], 16)
+        sz = printk_ringbuffer_type.get_type().sizeof
+        prb = utils.read_memoryview(inf, prb_addr, sz).tobytes()
+
+        # read in descriptor ring structure
+        off = printk_ringbuffer_type.get_type()['desc_ring'].bitpos // 8
+        addr = prb_addr + off
+        sz = prb_desc_ring_type.get_type().sizeof
+        desc_ring = utils.read_memoryview(inf, addr, sz).tobytes()
+
+        # read in descriptor array
+        off = prb_desc_ring_type.get_type()['count_bits'].bitpos // 8
+        desc_ring_count = 1 << utils.read_u32(desc_ring, off)
+        desc_sz = prb_desc_type.get_type().sizeof
+        off = prb_desc_ring_type.get_type()['descs'].bitpos // 8
+        addr = utils.read_ulong(desc_ring, off)
+        descs = utils.read_memoryview(inf, addr, desc_sz * desc_ring_count).tobytes()
+
+        # read in text data ring structure
+        off = printk_ringbuffer_type.get_type()['text_data_ring'].bitpos // 8
+        addr = prb_addr + off
+        sz = prb_data_ring_type.get_type().sizeof
+        text_data_ring = utils.read_memoryview(inf, addr, sz).tobytes()
+
+        # read in text data
+        off = prb_data_ring_type.get_type()['size_bits'].bitpos // 8
+        text_data_sz = 1 << utils.read_u32(text_data_ring, off)
+        off = prb_data_ring_type.get_type()['data'].bitpos // 8
+        addr = utils.read_ulong(text_data_ring, off)
+        text_data = utils.read_memoryview(inf, addr, text_data_sz).tobytes()
+
+        counter_off = atomic_long_type.get_type()['counter'].bitpos // 8
+
+        sv_off = prb_desc_type.get_type()['state_var'].bitpos // 8
+
+        off = prb_desc_type.get_type()['text_blk_lpos'].bitpos // 8
+        begin_off = off + (prb_data_blk_lpos_type.get_type()['begin'].bitpos // 8)
+        next_off = off + (prb_data_blk_lpos_type.get_type()['next'].bitpos // 8)
+
+        off = prb_desc_type.get_type()['info'].bitpos // 8
+        ts_off = off + printk_info_type.get_type()['ts_nsec'].bitpos // 8
+        len_off = off + printk_info_type.get_type()['text_len'].bitpos // 8
+
+        # definitions from kernel/printk/printk_ringbuffer.h
+        desc_sv_bits = utils.get_long_type().sizeof * 8
+        desc_committed_mask = 1 << (desc_sv_bits - 1)
+        desc_reuse_mask = 1 << (desc_sv_bits - 2)
+        desc_flags_mask = desc_committed_mask | desc_reuse_mask
+        desc_id_mask = ~desc_flags_mask
+
+        # read in tail and head descriptor ids
+        off = prb_desc_ring_type.get_type()['tail_id'].bitpos // 8
+        tail_id = utils.read_u64(desc_ring, off + counter_off)
+        off = prb_desc_ring_type.get_type()['head_id'].bitpos // 8
+        head_id = utils.read_u64(desc_ring, off + counter_off)
+
+        did = tail_id
+        while True:
+            ind = did % desc_ring_count
+            desc_off = desc_sz * ind
+
+            # skip non-committed record
+            state = utils.read_u64(descs, desc_off + sv_off + counter_off) & desc_flags_mask
+            if state != desc_committed_mask:
+                if did == head_id:
                     break
-                pos = log_buf_2nd_half
+                did = (did + 1) & desc_id_mask
                 continue
 
-            text_len = utils.read_u16(log_buf, pos + text_len_offset)
-            text_start = pos + text_offset
-            text = log_buf[text_start:text_start + text_len].decode(
-                encoding='utf8', errors='replace')
-            time_stamp = utils.read_u64(log_buf, pos + time_stamp_offset)
+            begin = utils.read_ulong(descs, desc_off + begin_off) % text_data_sz
+            end = utils.read_ulong(descs, desc_off + next_off) % text_data_sz
+
+            # handle data-less record
+            if begin & 1 == 1:
+                text = ""
+            else:
+                # handle wrapping data block
+                if begin > end:
+                    begin = 0
+
+                # skip over descriptor id
+                text_start = begin + utils.get_long_type().sizeof
+
+                text_len = utils.read_u16(descs, desc_off + len_off)
+
+                # handle truncated message
+                if end - text_start < text_len:
+                    text_len = end - text_start
+
+                text = text_data[text_start:text_start + text_len].decode(
+                    encoding='utf8', errors='replace')
+
+            time_stamp = utils.read_u64(descs, desc_off + ts_off)
 
             for line in text.splitlines():
                 msg = u"[{time:12.6f}] {line}\n".format(
@@ -75,7 +138,9 @@ class LxDmesg(gdb.Command):
                     msg = msg.encode(encoding='utf8', errors='replace')
                 gdb.write(msg)
 
-            pos += length
+            if did == head_id:
+                break
+            did = (did + 1) & desc_id_mask
 
 
 LxDmesg()