tracing/uprobes: Add @+file_offset fetch method

Enable to fetch data from a file offset.  Currently it only supports
fetching from same binary uprobe set.  It'll translate the file offset
to a proper virtual address in the process.

The syntax is "@+OFFSET" as it does similar to normal memory fetching
(@ADDR) which does no address translation.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: zhangwei(Jovi) <jovi.zhangwei@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

1 files changed, 12 insertions, 1 deletions

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index a130d612e705..8364a421b4df 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -374,7 +374,7 @@ static int parse_probe_arg(char *arg, const struct fetch_type *t,
                 }
                 break;
 
-        case '@':       /* memory or symbol */
+        case '@':       /* memory, file-offset or symbol */
                 if (isdigit(arg[1])) {
                         ret = kstrtoul(arg + 1, 0, &param);
                         if (ret)
@@ -382,6 +382,17 @@ static int parse_probe_arg(char *arg, const struct fetch_type *t,
 
                         f->fn = t->fetch[FETCH_MTD_memory];
                         f->data = (void *)param;
+                } else if (arg[1] == '+') {
+                        /* kprobes don't support file offsets */
+                        if (is_kprobe)
+                                return -EINVAL;
+
+                        ret = kstrtol(arg + 2, 0, &offset);
+                        if (ret)
+                                break;
+
+                        f->fn = t->fetch[FETCH_MTD_file_offset];
+                        f->data = (void *)offset;
                 } else {
                         /* uprobes don't support symbols */
                         if (!is_kprobe)