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tracing: expose current->comm to [ku]probe events

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ftrace is very quick to give up on saving the task command line (see
`trace_save_cmdline()`). The workaround for events which really care
about the command line is to explicitly assign it as part of the entry.
However, this doesn't work for kprobe events, as there's no
straightforward way to get access to current->comm. Add a kprobe/uprobe
event variable $comm which provides exactly that.

Link: http://lkml.kernel.org/r/f59b472033b943a370f5f48d0af37698f409108f.1465435894.git.osandov@fb.com

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Omar Sandoval
2016-06-08 18:38:02 -07:00
committed by Steven Rostedt
parent 345ddcc882
commit 35abb67de7
5 changed files with 50 additions and 0 deletions
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33
kernel/trace/trace_probe.c
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@@ -218,6 +218,28 @@ free_bitfield_fetch_param(struct bitfield_fetch_param *data)
kfree(data);
}
void FETCH_FUNC_NAME(comm, string)(struct pt_regs *regs,
void *data, void *dest)
{
int maxlen = get_rloc_len(*(u32 *)dest);
u8 *dst = get_rloc_data(dest);
long ret;
if (!maxlen)
return;
ret = strlcpy(dst, current->comm, maxlen);
*(u32 *)dest = make_data_rloc(ret, get_rloc_offs(*(u32 *)dest));
}
NOKPROBE_SYMBOL(FETCH_FUNC_NAME(comm, string));
void FETCH_FUNC_NAME(comm, string_size)(struct pt_regs *regs,
void *data, void *dest)
{
*(u32 *)dest = strlen(current->comm) + 1;
}
NOKPROBE_SYMBOL(FETCH_FUNC_NAME(comm, string_size));
static const struct fetch_type *find_fetch_type(const char *type,
const struct fetch_type *ftbl)
{
@@ -348,6 +370,11 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,
}
} else
ret = -EINVAL;
} else if (strcmp(arg, "comm") == 0) {
if (strcmp(t->name, "string") != 0 &&
strcmp(t->name, "string_size") != 0)
return -EINVAL;
f->fn = t->fetch[FETCH_MTD_comm];
} else
ret = -EINVAL;
@@ -522,6 +549,12 @@ int traceprobe_parse_probe_arg(char *arg, ssize_t *size,
arg[t - parg->comm] = '\0';
t++;
}
/*
* The default type of $comm should be "string", and it can't be
* dereferenced.
*/
if (!t && strcmp(arg, "$comm") == 0)
t = "string";
parg->type = find_fetch_type(t, ftbl);
if (!parg->type) {
pr_info("Unsupported type: %s\n", t);