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SubjectRe: kmemleak hexdump proposal
Hello.
This is actually draft. We'll discuss details during next merge window (or earlier).

Thanks.
---

hex dump prints not more than HEX_MAX_LINES lines by HEX_ROW_SIZE (16 or 32) bytes.
( min(object->size, HEX_MAX_LINES * HEX_ROW_SIZE) ).

Example (HEX_ROW_SIZE 16):

unreferenced object 0xf68b59b8 (size 32):
comm "swapper", pid 1, jiffies 4294877610
hex dump (first 32 bytes):
70 6e 70 20 30 30 3a 30 31 00 5a 5a 5a 5a 5a 5a pnp 00:01.ZZZZZZ
5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a a5 ZZZZZZZZZZZZZZZ.
backtrace:
[<c10e931b>] kmemleak_alloc+0x11b/0x2b0
[<c10e4bc1>] kmem_cache_alloc+0x111/0x1c0
[<c12c426e>] reserve_range+0x3e/0x1b0
[<c12c4474>] system_pnp_probe+0x94/0x140
[<c12bafa4>] pnp_device_probe+0x84/0x100
[<c12f1939>] driver_probe_device+0x89/0x170
[<c12f1ab9>] __driver_attach+0x99/0xa0
[<c12f1048>] bus_for_each_dev+0x58/0x90
[<c12f1784>] driver_attach+0x24/0x40
[<c12f0824>] bus_add_driver+0xc4/0x290
[<c12f1e30>] driver_register+0x70/0x130
[<c12bacf6>] pnp_register_driver+0x26/0x40
[<c15d671c>] pnp_system_init+0x1b/0x2e
[<c100115f>] do_one_initcall+0x3f/0x1a0
[<c15ac4af>] kernel_init+0x13e/0x1a6
[<c1003e07>] kernel_thread_helper+0x7/0x10


Example (HEX_ROW_SIZE 32):

unreferenced object 0xf5e2e130 (size 2048):
comm "modprobe", pid 2084, jiffies 4294880769
hex dump (first 64 bytes):
24 97 ff ff fc ff ff ff fc ff ff ff fc ff ff ff fc ff ff ff fc ff ff ff fc ff ff ff fc ff ff ff $...............................
fc ff ff ff fc ff ff ff fc ff ff ff fc ff ff ff fc ff ff ff fc ff ff ff fc ff ff ff fc ff ff ff ................................
backtrace:
[<c10e931b>] kmemleak_alloc+0x11b/0x2b0
[<c10e587d>] __kmalloc+0x16d/0x210
[<c10e73cd>] pcpu_mem_alloc+0x2d/0x80
[<c10e7482>] pcpu_extend_area_map+0x62/0x100
[<c10e7837>] pcpu_alloc+0x317/0x480
[<c10e79f7>] __alloc_percpu+0x17/0x30
[<c122fd54>] alloc_disk_node+0x54/0x150
[<c122fe6c>] alloc_disk+0x1c/0x40
[<fd61a25b>] loop_alloc+0x6b/0x170 [loop]
[<fd61e092>] 0xfd61e092
[<c100115f>] do_one_initcall+0x3f/0x1a0
[<c10785ad>] sys_init_module+0xdd/0x220
[<c100324b>] sysenter_do_call+0x12/0x22
[<ffffffff>] 0xffffffff
unreferenced object 0xf5d3cd00 (size 32):
comm "consolechars", pid 2433, jiffies 4294894598
hex dump (first 32 bytes):
60 15 58 c1 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a a5 `.X.....ZZZZZZZZZZZZZZZZZZZZZZZ.
backtrace:
[<c10e931b>] kmemleak_alloc+0x11b/0x2b0
[<c10e4bc1>] kmem_cache_alloc+0x111/0x1c0
[<c12cf49b>] tty_ldisc_try_get+0x2b/0x130
[<c12cf7d7>] tty_ldisc_get+0x37/0x70
[<c12cfa54>] tty_ldisc_reinit+0x34/0x70
[<c12cfac5>] tty_ldisc_release+0x35/0x60
[<c12ca1fe>] tty_release_dev+0x33e/0x500
[<c12ca3e0>] tty_release+0x20/0x40
[<c10ed61d>] __fput+0xed/0x200
[<c10ed752>] fput+0x22/0x40
[<c10e96c9>] filp_close+0x49/0x90
[<c1045445>] put_files_struct+0xb5/0xe0
[<c10454b5>] exit_files+0x45/0x60
[<c1046fd3>] do_exit+0x133/0x6c0
[<c10475a5>] do_group_exit+0x45/0xa0
[<c1047622>] sys_exit_group+0x22/0x40


hexdump.c can print prefix:
case DUMP_PREFIX_ADDRESS:
f6998df0: 3c 06 00 00 00 00 00 00 78 69 00 00 .... <.......xi......................
case DUMP_PREFIX_OFFSET:
00000000: 3c 06 00 00 00 00 00 00 78 69 00 00 .... <.......xi......................
default:
3c 06 00 00 00 00 00 00 78 69 00 00 00 00 00 .... <.......xi......................

hex_dump_object(struct seq_file *seq, struct kmemleak_object *object)
can be extended to accept prefix flag either. Though I don't think it's so important. So, it prints without any prefix.



diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 5063873..65c5d74 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -160,6 +160,15 @@ struct kmemleak_object {
/* flag set to not scan the object */
#define OBJECT_NO_SCAN (1 << 2)

+/* number of bytes to print per line; must be 16 or 32 */
+#define HEX_ROW_SIZE 32
+/* number of bytes to print at a time (1, 2, 4, 8) */
+#define HEX_GROUP_SIZE 1
+/* include ASCII after the hex output */
+#define HEX_ASCII 1
+/* max number of lines to be printed */
+#define HEX_MAX_LINES 2
+
/* the list of all allocated objects */
static LIST_HEAD(object_list);
/* the list of gray-colored objects (see color_gray comment below) */
@@ -181,6 +190,8 @@ static atomic_t kmemleak_initialized = ATOMIC_INIT(0);
static atomic_t kmemleak_early_log = ATOMIC_INIT(1);
/* set if a fata kmemleak error has occurred */
static atomic_t kmemleak_error = ATOMIC_INIT(0);
+/* set if hex dump should be printed */
+static atomic_t kmemleak_hex_dump = ATOMIC_INIT(1);

/* minimum and maximum address that may be valid pointers */
static unsigned long min_addr = ULONG_MAX;
@@ -258,6 +269,35 @@ static void kmemleak_disable(void);
kmemleak_disable(); \
} while (0)

+
+/*
+ * Printing of the objects hex dump to the seq file. The number on lines
+ * to be printed is limited to HEX_MAX_LINES to prevent seq file spamming.
+ * The actual number of printed bytes depends on HEX_ROW_SIZE.
+ * It must be called with the object->lock held.
+ */
+static void hex_dump_object(struct seq_file *seq,
+ struct kmemleak_object *object)
+{
+ const u8 *ptr = (const u8 *)object->pointer;
+ /* Limit the number of lines to HEX_MAX_LINES. */
+ int len = min(object->size, (size_t)(HEX_MAX_LINES * HEX_ROW_SIZE));
+ int i, remaining = len;
+ unsigned char linebuf[200];
+
+ seq_printf(seq, " hex dump (first %d bytes):\n", len);
+
+ for (i = 0; i < len; i += HEX_ROW_SIZE) {
+ int linelen = min(remaining, HEX_ROW_SIZE);
+ remaining -= HEX_ROW_SIZE;
+ hex_dump_to_buffer(ptr + i, linelen, HEX_ROW_SIZE,
+ HEX_GROUP_SIZE, linebuf,
+ sizeof(linebuf), HEX_ASCII);
+
+ seq_printf(seq, " %s\n", linebuf);
+ }
+}
+
/*
* Object colors, encoded with count and min_count:
* - white - orphan object, not enough references to it (count < min_count)
@@ -303,6 +343,11 @@ static void print_unreferenced(struct seq_file *seq,
object->pointer, object->size);
seq_printf(seq, " comm \"%s\", pid %d, jiffies %lu\n",
object->comm, object->pid, object->jiffies);
+
+ /* check whether hex dump should be printed */
+ if (atomic_read(&kmemleak_hex_dump))
+ hex_dump_object(seq, object);
+
seq_printf(seq, " backtrace:\n");

for (i = 0; i < object->trace_len; i++) {
@@ -1269,6 +1314,10 @@ static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
start_scan_thread();
else if (strncmp(buf, "scan=off", 8) == 0)
stop_scan_thread();
+ else if (strncmp(buf, "hexdump=on", 10) == 0)
+ atomic_set(&kmemleak_hex_dump, 1);
+ else if (strncmp(buf, "hexdump=off", 11) == 0)
+ atomic_set(&kmemleak_hex_dump, 0);
else if (strncmp(buf, "scan=", 5) == 0) {
unsigned long secs;
int err;

Sergey


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