kdump: fix dmesg gdbmacro to work with record based printk

Commit 7ff9554bb578 ("printk: convert byte-buffer to variable-length
record buffer") introduced a record based printk buffer. Modify
gdbmacros.txt to parse this new structure so dmesg will work properly.

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Corey Minyard <[e-mail]>
Cc: Dave Young <[e-mail]>
Cc: Baoquan He <[e-mail]>
Cc: Vivek Goyal <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/kdump/gdbmacros.txt

···
 	address the kernel panicked.
 end
 
+define dump_log_idx
+	set $idx = $arg0
+	if ($argc > 1)
+		set $prev_flags = $arg1
+	else
+		set $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 $prefix = 0
+	end
+
+	# msg->flags & LOG_CONT
+	if ($msg->flags & 8)
+		# (prev & LOG_CONT && !(prev & LOG_NEWLINE))
+		if (($prev_flags & 8) && !($prev_flags & 2))
+			set $prefix = 0
+		end
+		# (!(msg->flags & LOG_NEWLINE))
+		if (!($msg->flags & 2))
+			set $newline = 0
+		end
+	end
+
+	if ($prefix)
+		printf "[%5lu.%06lu] ", $msg->ts_nsec / 1000000000, $msg->ts_nsec % 1000000000
+	end
+	if ($msg->text_len != 0)
+		eval "printf \"%%%d.%ds\", $log", $msg->text_len, $msg->text_len
+	end
+	if ($newline)
+		printf "\n"
+	end
+	if ($msg->dict_len > 0)
+		set $dict = $log + $msg->text_len
+		set $idx = 0
+		set $line = 1
+		while ($idx < $msg->dict_len)
+			if ($line)
+				printf " "
+				set $line = 0
+			end
+			set $c = $dict[$idx]
+			if ($c == '\0')
+				printf "\n"
+				set $line = 1
+			else
+				if ($c < ' ' || $c >= 127 || $c == '\\')
+					printf "\\x%02x", $c
+				else
+					printf "%c", $c
+				end
+			end
+			set $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.
+end
 
 define dmesg
-	set $i = 0
-	set $end_idx = (log_end - 1) & (log_buf_len - 1)
+	set $i = log_first_idx
+	set $end_idx = log_first_idx
+	set $prev_flags = 0
 
-	while ($i < logged_chars)
-		set $idx = (log_end - 1 - logged_chars + $i) & (log_buf_len - 1)
-
-		if ($idx + 100 <= $end_idx) || \
-		   ($end_idx <= $idx && $idx + 100 < log_buf_len)
-			printf "%.100s", &log_buf[$idx]
-			set $i = $i + 100
+	while (1)
+		set $msg = ((struct printk_log *) (log_buf + $i))
+		if ($msg->len == 0)
+			set $i = 0
 		else
-			printf "%c", log_buf[$idx]
-			set $i = $i + 1
+			dump_log_idx $i $prev_flags
+			set $i = $i + $msg->len
+			set $prev_flags = $msg->flags
+		end
+		if ($i == $end_idx)
+			loop_break
 		end
 	end
 end