Add "log -c" option to display printk caller id

Add support so that dmesg entries include the optional Linux Kernel
debug CONFIG option PRINTK_CALLER which adds an optional dmesg field
that contains the Thread Id or CPU Id that is issuing the printk to
add the message to the kernel ring buffer. If enabled, this CONFIG
option makes debugging simpler as dmesg entries for a specific
thread or CPU can be recognized. The config option was introduced
with Linux 5.1 [1].

Size of the PRINTK_CALLER field is determined by the maximum number
tasks that can be run on the system which is limited by the value of
/proc/sys/kernel/pid_max as pid values are from 0 to value - 1.
This value determines the number of id digits needed by the caller id.
The PRINTK_CALLER field is printed as T<id> for a Task Id or C<id>
for a CPU Id for a printk in CPU context. The values are left space
padded and enclosed in parentheses such as:
         [    T123]   or   [     C16]

Our patch adds the PRINTK_CALLER field after the timestamp if the
printk caller log / dmesg option (-c) is selected:

  crash> log -m -c
  ...
  [    0.014179] [     T1] <6>Secure boot disabled
  [    0.014179] [    T29] <6>RAMDISK: [mem 0x3cf4f000-0x437bbfff]
  ...

[1] 15ff2069cb7f ("printk: Add caller information to printk() output.")

Resolves: crash-utility#164
Signed-off-by: Ivan Delalande <[email protected]>
Signed-off-by: Edward Chron <[email protected]>
Signed-off-by: Kazuhito Hagio <[email protected]>

defs.h

@@ -2239,6 +2239,7 @@ struct offset_table {                    /* stash of commonly-used offsets */
 	long mnt_namespace_mounts;
 	long mnt_namespace_nr_mounts;
 	long mount_mnt_node;
+	long log_caller_id;
 };
 
 struct size_table {         /* stash of commonly-used sizes */
@@ -6108,12 +6109,13 @@ void dump_log(int);
 void parse_kernel_version(char *);
 
 #define LOG_LEVEL(v) ((v) & 0x07)
-#define SHOW_LOG_LEVEL (0x1)
-#define SHOW_LOG_DICT  (0x2)
-#define SHOW_LOG_TEXT  (0x4)
-#define SHOW_LOG_AUDIT (0x8)
-#define SHOW_LOG_CTIME (0x10)
-#define SHOW_LOG_SAFE  (0x20)
+#define SHOW_LOG_LEVEL    (0x1)
+#define SHOW_LOG_DICT     (0x2)
+#define SHOW_LOG_TEXT     (0x4)
+#define SHOW_LOG_AUDIT    (0x8)
+#define SHOW_LOG_CTIME   (0x10)
+#define SHOW_LOG_SAFE    (0x20)
+#define SHOW_LOG_CALLER  (0x40)
 void set_cpu(int);
 void clear_machdep_cache(void);
 struct stack_hook *gather_text_list(struct bt_info *);
@@ -7588,6 +7590,10 @@ int calc_kaslr_offset(ulong *, ulong *);
  */
 void dump_lockless_record_log(int);
 
+/* caller_id default and max character sizes based on pid field size */
+#define PID_CHARS_MAX 16        /* Max Number of PID characters */
+#define PID_CHARS_DEFAULT 8     /* Default number of PID characters */
+
 /*
  *  gnu_binutils.c
  */

help.c

@@ -4024,7 +4024,7 @@ NULL
 char *help_log[] = {
 "log",
 "dump system message buffer",
-"[-Ttdmas]",
+"[-Ttdmasc]",
 "  This command dumps the kernel log_buf contents in chronological order.  The",
 "  command supports the older log_buf formats, which may or may not contain a",
 "  timestamp inserted prior to each message, as well as the newer variable-length", 
@@ -4047,7 +4047,11 @@ char *help_log[] = {
 "        been copied out to the user-space audit daemon.",
 "    -s  Dump the printk logs remaining in kernel safe per-CPU buffers that",
 "        have not been flushed out to log_buf.",
-" ",        
+"    -c  Display the caller id field that identifies either the thread id or",
+"        the CPU id (if in CPU context) that called printk(), if available.",
+"        Generally available on Linux 5.1 to 5.9 kernels configured with",
+"        CONFIG_PRINTK_CALLER or Linux 5.10 and later kernels.",
+" ",
 "\nEXAMPLES",
 "  Dump the kernel message buffer:\n",
 "    %s> log",
@@ -4215,6 +4219,17 @@ char *help_log[] = {
 "    CPU: 0  ADDR: ffff8ca4fbc1ad00 LEN: 0  MESSAGE_LOST: 0",
 "      (empty)",
 "    ...",
+" ",
+"  Display the caller id that identifies the thread id of the task (begins",
+"  with 'T') or the processor id (begins with 'C' for in CPU context) that",
+"  called printk(), if available.\n",
+"    %s> log -c",
+"    ...",
+"    [    0.014179] [     T1] Secure boot disabled",
+"    [    0.014179] [    T29] RAMDISK: [mem 0x3cf4f000-0x437bbfff]",
+"    [    0.198789] [     C0] DMAR: DRHD: handling fault status reg 3",
+"    ...",
+
 NULL               
 };
 

kernel.c

@@ -5089,7 +5089,7 @@ cmd_log(void)
 
 	msg_flags = 0;
 
-        while ((c = getopt(argcnt, args, "Ttdmas")) != EOF) {
+        while ((c = getopt(argcnt, args, "Ttdmasc")) != EOF) {
                 switch(c)
                 {
 		case 'T':
@@ -5110,6 +5110,9 @@ cmd_log(void)
 		case 's':
 			msg_flags |= SHOW_LOG_SAFE;
 			break;
+		case 'c':
+			msg_flags |= SHOW_LOG_CALLER;
+			break;
                 default:
                         argerrs++;
                         break;
@@ -5369,6 +5372,25 @@ dump_log_entry(char *logptr, int msg_flags)
 		fprintf(fp, "%s", buf);
 	}
 
+	/*
+	 * The PRINTK_CALLER id field was introduced with Linux-5.1 so if
+	 * requested, Kernel version >= 5.1 and field exists print caller_id.
+	 */
+	if (msg_flags & SHOW_LOG_CALLER &&
+			VALID_MEMBER(log_caller_id)) {
+		const unsigned int cpuid = 0x80000000;
+		char cbuf[PID_CHARS_MAX];
+		unsigned int cid;
+
+		/* Get id type, isolate just id value in cid for print */
+		cid = UINT(logptr + OFFSET(log_caller_id));
+		sprintf(cbuf, "%c%d", (cid & cpuid) ? 'C' : 'T', cid & ~cpuid);
+		sprintf(buf, "[%*s] ", PID_CHARS_DEFAULT, cbuf);
+
+		ilen += strlen(buf);
+		fprintf(fp, "%s", buf);
+	}
+
 	level = LOG_LEVEL(level);
 
 	if (msg_flags & SHOW_LOG_LEVEL) {
@@ -5424,6 +5446,7 @@ dump_variable_length_record_log(int msg_flags)
 			 * from log to printk_log.  See 62e32ac3505a0cab.
 			 */
 			log_struct_name = "printk_log";
+			MEMBER_OFFSET_INIT(log_caller_id, "printk_log", "caller_id");
 		} else 
 			log_struct_name = "log";
 

printk.c

@@ -9,6 +9,7 @@ struct prb_map {
 	unsigned long desc_ring_count;
 	char *descs;
 	char *infos;
+	unsigned int pid_max_chars;
 
 	char *text_data_ring;
 	unsigned long text_data_ring_size;
@@ -162,6 +163,24 @@ dump_record(struct prb_map *m, unsigned long id, int msg_flags)
 		fprintf(fp, "%s", buf);
 	}
 
+	/*
+	 * The lockless ringbuffer introduced in Linux-5.10 always has
+	 * the caller_id field available, so if requested, print it.
+	 */
+	if (msg_flags & SHOW_LOG_CALLER) {
+		const unsigned int cpuid = 0x80000000;
+		char cbuf[PID_CHARS_MAX];
+		unsigned int cid;
+
+		/* Get id type, isolate id value in cid for print */
+		cid = UINT(info + OFFSET(printk_info_caller_id));
+		sprintf(cbuf, "%c%d", (cid & cpuid) ? 'C' : 'T', cid & ~cpuid);
+		sprintf(buf, "[%*s] ", m->pid_max_chars, cbuf);
+
+		ilen += strlen(buf);
+		fprintf(fp, "%s", buf);
+	}
+
 	if (msg_flags & SHOW_LOG_LEVEL) {
 		level = UCHAR(info + OFFSET(printk_info_level)) >> 5;
 		sprintf(buf, "<%x>", level);
@@ -262,6 +281,21 @@ dump_lockless_record_log(int msg_flags)
 		goto out_text_data;
 	}
 
+	/* If caller_id was requested, get the pid_max value for print */
+	if (msg_flags & SHOW_LOG_CALLER) {
+		unsigned int pidmax;
+
+		get_symbol_data("pid_max", sizeof(pidmax), &pidmax);
+		if (pidmax <= 99999)
+			m.pid_max_chars = 6;
+		else if (pidmax <= 999999)
+			m.pid_max_chars = 7;
+		else
+			m.pid_max_chars = PID_CHARS_DEFAULT;
+	} else {
+		m.pid_max_chars = PID_CHARS_DEFAULT;
+	}
+
 	/* ready to go */
 
 	tail_id = ULONG(m.desc_ring + OFFSET(prb_desc_ring_tail_id) +

symbols.c

@@ -11550,6 +11550,7 @@ dump_offset_table(char *spec, ulong makestruct)
 		OFFSET(log_level));
 	fprintf(fp, "               log_flags_level: %ld\n",
 		OFFSET(log_flags_level));
+	fprintf(fp, "                 log_caller_id: %ld\n", OFFSET(log_caller_id));
 
 	fprintf(fp, "               printk_info_seq: %ld\n", OFFSET(printk_info_seq));
 	fprintf(fp, "           printk_info_ts_nseq: %ld\n", OFFSET(printk_info_ts_nsec));