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Subject[PATCH 12/20 v2] tracing: Add accessing direct address from function based events
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

Allow referencing any address during the function based event. The syntax is
to use <type> <name>=<addr> For example:

# echo 'do_IRQ(long total_forks=0xffffffffa2a4b4c0)' > function_events
# echo 1 > events/function/enable
# cat trace
sshd-832 [000] d... 221639.210845: ret_from_intr->do_IRQ(total_forks=855)
sshd-832 [000] d... 221639.211114: ret_from_intr->do_IRQ(total_forks=855)
<idle>-0 [000] d... 221639.211198: ret_from_intr->do_IRQ(total_forks=855)

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
Documentation/trace/function-based-events.rst | 40 +++++++-
kernel/trace/trace_event_ftrace.c | 129 +++++++++++++++++++++-----
2 files changed, 143 insertions(+), 26 deletions(-)

diff --git a/Documentation/trace/function-based-events.rst b/Documentation/trace/function-based-events.rst
index f18c8f3ef330..b0e6725f3032 100644
--- a/Documentation/trace/function-based-events.rst
+++ b/Documentation/trace/function-based-events.rst
@@ -91,7 +91,7 @@ as follows:

ARGS := ARG | ARG ',' ARGS | ''

- ARG := TYPE FIELD | ARG '|' ARG
+ ARG := TYPE FIELD | TYPE <name> '=' ADDR | TYPE ADDR | ARG '|' ARG

TYPE := ATOM | 'unsigned' ATOM

@@ -107,6 +107,8 @@ as follows:

OFFSET := '+' <number>

+ ADDR := A hexidecimal address starting with '0x'
+
Where <name> is a unique string starting with an alphabetic character
and consists only of letters and numbers and underscores.

@@ -267,3 +269,39 @@ Again, using gdb to find the offset of the "func" field of struct work_struct
<idle>-0 [000] dNs3 6241.172004: delayed_work_timer_fn->__queue_work(cpu=128, wq=ffff88011a010800, func=vmstat_shepherd+0x0/0xb0)
worker/0:2-1689 [000] d..2 6241.172026: __queue_delayed_work->__queue_work(cpu=7, wq=ffff88011a11da00, func=vmstat_update+0x0/0x70)
<idle>-0 [005] d.s3 6241.347996: queue_work_on->__queue_work(cpu=128, wq=ffff88011a011200, func=fb_flashcursor+0x0/0x110 [fb])
+
+
+Direct memory access
+====================
+
+Function arguments are not the only thing that can be recorded from a function
+based event. Memory addresses can also be examined. If there's a global variable
+that you want to monitor via an interrupt, you can put in the address directly.
+
+ # grep total_forks /proc/kallsyms
+ffffffff82354c18 B total_forks
+
+ # echo 'do_IRQ(int total_forks=0xffffffff82354c18)' > function_events
+
+ # echo 1 events/functions/do_IRQ/enable
+ # cat trace
+ <idle>-0 [003] d..3 337.076709: ret_from_intr->do_IRQ(total_forks=1419)
+ <idle>-0 [003] d..3 337.077046: ret_from_intr->do_IRQ(total_forks=1419)
+ <idle>-0 [003] d..3 337.077076: ret_from_intr->do_IRQ(total_forks=1420)
+
+Note, address notations do not affect the argument count. For instance, with
+
+__visible unsigned int __irq_entry do_IRQ(struct pt_regs *regs)
+
+ # echo 'do_IRQ(int total_forks=0xffffffff82354c18, symbol regs[16])' > function_events
+
+Is the same as
+
+ # echo 'do_IRQ(int total_forks=0xffffffff82354c18 | symbol regs[16])' > function_events
+
+ # cat trace
+ <idle>-0 [003] d..3 653.839546: ret_from_intr->do_IRQ(total_forks=1504, regs=cpuidle_enter_state+0xb1/0x330)
+ <idle>-0 [003] d..3 653.906011: ret_from_intr->do_IRQ(total_forks=1504, regs=cpuidle_enter_state+0xb1/0x330)
+ <idle>-0 [003] d..3 655.823498: ret_from_intr->do_IRQ(total_forks=1504, regs=tick_nohz_idle_enter+0x4c/0x50)
+ <idle>-0 [003] d..3 655.954096: ret_from_intr->do_IRQ(total_forks=1504, regs=cpuidle_enter_state+0xb1/0x330)
+
diff --git a/kernel/trace/trace_event_ftrace.c b/kernel/trace/trace_event_ftrace.c
index 1359f714a1b1..97748edc8bcb 100644
--- a/kernel/trace/trace_event_ftrace.c
+++ b/kernel/trace/trace_event_ftrace.c
@@ -63,6 +63,8 @@ enum func_states {
FUNC_STATE_BRACKET_END,
FUNC_STATE_INDIRECT,
FUNC_STATE_UNSIGNED,
+ FUNC_STATE_ADDR,
+ FUNC_STATE_EQUAL,
FUNC_STATE_PIPE,
FUNC_STATE_PLUS,
FUNC_STATE_TYPE,
@@ -201,6 +203,7 @@ static char *next_token(char **ptr, char *last)
*str == ',' ||
*str == '|' ||
*str == '+' ||
+ *str == '=' ||
*str == ')')
break;
}
@@ -245,12 +248,39 @@ static int add_arg(struct func_event *fevent, int ftype, int unsign)
arg->sign = func_type->sign;
arg->offset = ALIGN(fevent->arg_offset, arg->size);
arg->func_type = ftype;
- arg->arg = fevent->arg_cnt;
fevent->arg_offset = arg->offset + arg->size;

list_add_tail(&arg->list, &fevent->args);
fevent->last_arg = arg;
- fevent->arg_cnt++;
+
+ return 0;
+}
+
+static int update_arg_name(struct func_event *fevent, const char *name)
+{
+ struct func_arg *arg = fevent->last_arg;
+
+ if (WARN_ON(!arg))
+ return -EINVAL;
+
+ arg->name = kstrdup(name, GFP_KERNEL);
+ if (!arg->name)
+ return -ENOMEM;
+ return 0;
+}
+
+static int update_arg_arg(struct func_event *fevent)
+{
+ struct func_arg *arg = fevent->last_arg;
+
+ if (WARN_ON(!arg))
+ return -EINVAL;
+
+ /* Make sure the arch can support this many args */
+ if (fevent->arg_cnt >= max_args)
+ return -EINVAL;
+
+ arg->arg = fevent->arg_cnt;

return 0;
}
@@ -258,14 +288,16 @@ static int add_arg(struct func_event *fevent, int ftype, int unsign)
static enum func_states
process_event(struct func_event *fevent, const char *token, enum func_states state)
{
+ static bool update_arg;
static int unsign;
- long val;
+ unsigned long val;
int ret;
int i;

switch (state) {
case FUNC_STATE_INIT:
unsign = 0;
+ update_arg = false;
if (!isalpha(token[0]) && token[0] != '_')
break;
/* Do not allow wild cards */
@@ -281,15 +313,15 @@ process_event(struct func_event *fevent, const char *token, enum func_states sta
break;
return FUNC_STATE_PARAM;

- case FUNC_STATE_PIPE:
- fevent->arg_cnt--;
- goto comma;
case FUNC_STATE_PARAM:
if (token[0] == ')')
return FUNC_STATE_END;
/* Fall through */
case FUNC_STATE_COMMA:
- comma:
+ if (update_arg)
+ fevent->arg_cnt++;
+ update_arg = false;
+ case FUNC_STATE_PIPE:
if (strcmp(token, "unsigned") == 0) {
unsign = 2;
return FUNC_STATE_UNSIGNED;
@@ -309,18 +341,20 @@ process_event(struct func_event *fevent, const char *token, enum func_states sta
return FUNC_STATE_TYPE;

case FUNC_STATE_TYPE:
- if (!isalpha(token[0]) || token[0] == '_')
- break;
if (WARN_ON(!fevent->last_arg))
break;
- fevent->last_arg->name = kstrdup(token, GFP_KERNEL);
- if (!fevent->last_arg->name)
+ if (update_arg_name(fevent, token) < 0)
+ break;
+ if (strncmp(token, "0x", 2) == 0)
+ goto equal;
+ if (!isalpha(token[0]) && token[0] != '_')
break;
+ update_arg = true;
return FUNC_STATE_VAR;

case FUNC_STATE_BRACKET:
WARN_ON(!fevent->last_arg);
- ret = kstrtol(token, 0, &val);
+ ret = kstrtoul(token, 0, &val);
if (ret)
break;
val *= fevent->last_arg->size;
@@ -335,7 +369,7 @@ process_event(struct func_event *fevent, const char *token, enum func_states sta
case FUNC_STATE_BRACKET_END:
switch (token[0]) {
case ')':
- return FUNC_STATE_END;
+ goto end;
case ',':
return FUNC_STATE_COMMA;
case '|':
@@ -346,16 +380,33 @@ process_event(struct func_event *fevent, const char *token, enum func_states sta
case FUNC_STATE_PLUS:
if (WARN_ON(!fevent->last_arg))
break;
- ret = kstrtol(token, 0, &val);
+ ret = kstrtoul(token, 0, &val);
if (ret)
break;
fevent->last_arg->index += val;
return FUNC_STATE_VAR;

+ case FUNC_STATE_ADDR:
+ switch (token[0]) {
+ case ')':
+ goto end;
+ case ',':
+ return FUNC_STATE_COMMA;
+ case '|':
+ return FUNC_STATE_PIPE;
+ }
+ break;
+
case FUNC_STATE_VAR:
+ if (token[0] == '=')
+ return FUNC_STATE_EQUAL;
+ if (WARN_ON(!fevent->last_arg))
+ break;
+ update_arg_arg(fevent);
+ update_arg = true;
switch (token[0]) {
case ')':
- return FUNC_STATE_END;
+ goto end;
case ',':
return FUNC_STATE_COMMA;
case '|':
@@ -367,10 +418,29 @@ process_event(struct func_event *fevent, const char *token, enum func_states sta
}
break;

+ case FUNC_STATE_EQUAL:
+ if (strncmp(token, "0x", 2) != 0)
+ break;
+ equal:
+ if (WARN_ON(!fevent->last_arg))
+ break;
+ ret = kstrtoul(token, 0, &val);
+ if (ret < 0)
+ break;
+ update_arg = false;
+ fevent->last_arg->index = val;
+ fevent->last_arg->arg = -1;
+ fevent->last_arg->indirect = INDIRECT_FLAG;
+ return FUNC_STATE_ADDR;
+
default:
break;
}
return FUNC_STATE_ERROR;
+ end:
+ if (update_arg)
+ fevent->arg_cnt++;
+ return FUNC_STATE_END;
}

static long long get_arg(struct func_arg *arg, unsigned long val)
@@ -419,7 +489,7 @@ static void func_event_trace(struct trace_event_file *trace_file,
long args[func_event->arg_cnt];
long long val = 1;
unsigned long irq_flags;
- int nr_args;
+ int nr_args = 0;
int size;
int pc;

@@ -440,12 +510,17 @@ static void func_event_trace(struct trace_event_file *trace_file,
entry = ring_buffer_event_data(event);
entry->ip = ip;
entry->parent_ip = parent_ip;
- nr_args = arch_get_func_args(pt_regs, 0, func_event->arg_cnt, args);
+ if (func_event->arg_cnt)
+ nr_args = arch_get_func_args(pt_regs, 0, func_event->arg_cnt, args);

list_for_each_entry(arg, &func_event->args, list) {
- if (arg->arg < nr_args)
- val = get_arg(arg, args[arg->arg]);
- else
+ if (arg->arg < nr_args) {
+ /* Is arg an address and not a parameter? */
+ if (arg->arg < 0)
+ val = get_arg(arg, 0);
+ else
+ val = get_arg(arg, args[arg->arg]);
+ } else
val = 0;
memcpy(&entry->data[arg->offset], &val, arg->size);
}
@@ -817,11 +892,15 @@ static int func_event_seq_show(struct seq_file *m, void *v)
last_arg = arg->arg;
comma = true;
seq_printf(m, "%s %s", arg->type, arg->name);
- if (arg->index)
- seq_printf(m, "+%ld", arg->index);
- if (arg->indirect && arg->size)
- seq_printf(m, "[%ld]",
- (arg->indirect ^ INDIRECT_FLAG) / arg->size);
+ if (arg->arg < 0) {
+ seq_printf(m, "=0x%lx", arg->index);
+ } else {
+ if (arg->index)
+ seq_printf(m, "+%ld", arg->index);
+ if (arg->indirect && arg->size)
+ seq_printf(m, "[%ld]",
+ (arg->indirect ^ INDIRECT_FLAG) / arg->size);
+ }
}
seq_puts(m, ")\n");

--
2.15.1

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