perf probe: Add kernel source path option

The probe plugin requires access to the source code for some operations.  The
source code must be in the exact same location as specified by the DWARF tags,
but sometimes the location is an absolute path that cannot be replicated by a
normal user. This change adds the -s|--source option to allow the user to
specify the root of the kernel source tree.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Masami Hiramatsu <mhiramat@redhat.com>
LKML-Reference: <1276543590-10486-1-git-send-email-chase.douglas@canonical.com>
Signed-off-by: Chase Douglas <chase.douglas@canonical.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-probe.txt

@@ -31,6 +31,10 @@ OPTIONS
 --vmlinux=PATH::
 	Specify vmlinux path which has debuginfo (Dwarf binary).
 
+-s::
+--source=PATH::
+	Specify path to kernel source.
+
 -v::
 --verbose::
         Be more verbose (show parsed arguments, etc).

tools/perf/builtin-probe.c

@@ -182,6 +182,8 @@ static const struct option options[] = {
 		     "Show source code lines.", opt_show_lines),
 	OPT_STRING('k', "vmlinux", &symbol_conf.vmlinux_name,
 		   "file", "vmlinux pathname"),
+	OPT_STRING('s', "source", &symbol_conf.source_prefix,
+		   "directory", "path to kernel source"),
 #endif
 	OPT__DRY_RUN(&probe_event_dry_run),
 	OPT_INTEGER('\0', "max-probes", &params.max_probe_points,

tools/perf/util/probe-finder.c

@@ -37,6 +37,7 @@
 #include "event.h"
 #include "debug.h"
 #include "util.h"
+#include "symbol.h"
 #include "probe-finder.h"
 
 /* Kprobe tracer basic type is up to u64 */
@@ -57,6 +58,55 @@ static int strtailcmp(const char *s1, const char *s2)
 	return 0;
 }
 
+/*
+ * Find a src file from a DWARF tag path. Prepend optional source path prefix
+ * and chop off leading directories that do not exist. Result is passed back as
+ * a newly allocated path on success.
+ * Return 0 if file was found and readable, -errno otherwise.
+ */
+static int get_real_path(const char *raw_path, char **new_path)
+{
+	if (!symbol_conf.source_prefix) {
+		if (access(raw_path, R_OK) == 0) {
+			*new_path = strdup(raw_path);
+			return 0;
+		} else
+			return -errno;
+	}
+
+	*new_path = malloc((strlen(symbol_conf.source_prefix) +
+			    strlen(raw_path) + 2));
+	if (!*new_path)
+		return -ENOMEM;
+
+	for (;;) {
+		sprintf(*new_path, "%s/%s", symbol_conf.source_prefix,
+			raw_path);
+
+		if (access(*new_path, R_OK) == 0)
+			return 0;
+
+		switch (errno) {
+		case ENAMETOOLONG:
+		case ENOENT:
+		case EROFS:
+		case EFAULT:
+			raw_path = strchr(++raw_path, '/');
+			if (!raw_path) {
+				free(*new_path);
+				*new_path = NULL;
+				return -ENOENT;
+			}
+			continue;
+
+		default:
+			free(*new_path);
+			*new_path = NULL;
+			return -errno;
+		}
+	}
+}
+
 /* Line number list operations */
 
 /* Add a line to line number list */
@@ -1096,11 +1146,13 @@ int find_perf_probe_point(int fd, unsigned long addr,
 static int line_range_add_line(const char *src, unsigned int lineno,
 			       struct line_range *lr)
 {
+	int ret;
+
 	/* Copy real path */
 	if (!lr->path) {
-		lr->path = strdup(src);
-		if (lr->path == NULL)
-			return -ENOMEM;
+		ret = get_real_path(src, &lr->path);
+		if (ret != 0)
+			return ret;
 	}
 	return line_list__add_line(&lr->line_list, lineno);
 }

tools/perf/util/symbol.h

@@ -71,6 +71,7 @@ struct symbol_conf {
 			full_paths,
 			show_cpu_utilization;
 	const char	*vmlinux_name,
+			*source_prefix,
 			*field_sep;
 	const char	*default_guest_vmlinux_name,
 			*default_guest_kallsyms,