[PATCH] Print absolute paths in printpathn when -yy is used

[zubin.mithra at gmail.com]

From: Zubin Mithra <zubin.mithra at gmail.com>

* defs.h (show_fd_path): Change type to unsigned int.
(get_tracee_cwd, print_abspath): New prototypes.
* strace.c (show_fd_path): Update usage to count y flag.
* util.c (get_tracee_cwd): New function.
(printpathn): Update to use get_tracee_cwd and print
  absolute path.

Signed-off-by: Zubin Mithra <zubin.mithra at gmail.com>
---
 defs.h   |  4 +++-
 strace.c |  4 ++--
 util.c   | 50 +++++++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 54 insertions(+), 4 deletions(-)

diff --git a/defs.h b/defs.h
index 1a3b483..62b86cd 100644
--- a/defs.h
+++ b/defs.h
@@ -562,7 +562,7 @@ extern bool iflag;
 extern bool count_wallclock;
 extern unsigned int qflag;
 extern bool not_failing_only;
-extern bool show_fd_path;
+extern unsigned int show_fd_path;
 extern bool hide_log_until_execve;
 /* are we filtering traces based on paths? */
 extern const char **paths_selected;
@@ -646,6 +646,8 @@ extern const char *signame(int);
 extern void pathtrace_select(const char *);
 extern int pathtrace_match(struct tcb *);
 extern int getfdpath(struct tcb *, int, char *, unsigned);
+extern int get_tracee_cwd(struct tcb *, char *);
+extern bool print_abspath(struct tcb *, char *, int);
 
 extern const char *xlookup(const struct xlat *, int);
 
diff --git a/strace.c b/strace.c
index 46c9d63..a17506a 100644
--- a/strace.c
+++ b/strace.c
@@ -129,7 +129,7 @@ static int post_attach_sigstop = TCB_IGNORE_ONE_SIGSTOP;
 bool not_failing_only = 0;
 
 /* Show path associated with fd arguments */
-bool show_fd_path = 0;
+unsigned int show_fd_path = 0;
 
 static bool detach_on_execve = 0;
 /* Are we "strace PROG" and need to skip detach on first execve? */
@@ -1734,7 +1734,7 @@ init(int argc, char *argv[])
 			xflag++;
 			break;
 		case 'y':
-			show_fd_path = 1;
+			show_fd_path++;
 			break;
 		case 'v':
 			qualify("abbrev=none");
diff --git a/util.c b/util.c
index 33482d5..583c395 100644
--- a/util.c
+++ b/util.c
@@ -571,7 +571,9 @@ void
 printpathn(struct tcb *tcp, long addr, int n)
 {
 	char path[MAXPATHLEN + 1];
+	char cwd[MAXPATHLEN + 1];
 	int nul_seen;
+	int valid_length = 1;
 
 	if (!addr) {
 		tprints("NULL");
@@ -593,8 +595,28 @@ printpathn(struct tcb *tcp, long addr, int n)
 		n++;
 		outstr = alloca(4 * n); /* 4*(n-1) + 3 for quotes and NUL */
 		string_quote(path, outstr, -1, n);
+
+		/* If -yy is used and the path is not absolute, find the cwd of the tracee
+		   and print that out first */
+		if (show_fd_path == 2 && outstr[1] != '/') {
+			/* If the call to get_tracee_cwd succeeds, we concatenate the
+			   cwd and outstr and print it out. If the call fails, we just
+			   print out the relative path. */
+			char *outcwd;
+			int cwd_len;
+			cwd_len = get_tracee_cwd(tcp, cwd);
+			if (cwd_len != -1) {
+				outcwd = alloca(4 * cwd_len);
+				string_quote(cwd, outcwd, -1, cwd_len+1);
+				outcwd[strlen(outcwd)-1] = '\0';
+				tprintf("%s", outcwd);
+				if (strlen(cwd) + strlen(outstr) > MAXPATHLEN)
+					valid_length = 0;
+			}
+		}
+		if (show_fd_path == 2) outstr += 1;
 		tprints(outstr);
-		if (!nul_seen)
+		if (!nul_seen || (show_fd_path==2) && !valid_length)
 			tprints("...");
 	}
 }
@@ -1549,3 +1571,29 @@ clearbpt(struct tcb *tcp)
 	tcp->flags &= ~TCB_BPTSET;
 	return 0;
 }
+
+/* Return the current working directory of the tracee process,
+   with a trailing slash. */
+int
+get_tracee_cwd(struct tcb *tcp, char *cwd)
+{
+	int link_size = sizeof("/proc/%u/cwd") + sizeof(int) * 3;
+	char linkpath[link_size];
+	ssize_t n;
+
+	snprintf(linkpath, link_size, "/proc/%u/cwd", tcp->pid);
+	n = readlink(linkpath, cwd, MAXPATHLEN);
+
+	/* If readlink fails, something is abnormal(path > 4096) about
+	   the traced process and its cwd, so return an empty cwd. */
+	if (n == -1) {
+		cwd[0] = '\0';
+		return n;
+	}
+
+	if (n >= 0) {
+		cwd[n] = '/';
+		cwd[n+1] = '\0';
+	}
+	return n+1;
+}
-- 
1.8.4