>From 5c2c2717e4bd8cf8a9f816c043e102e317e1d949 Mon Sep 17 00:00:00 2001
From: Quentin Rameau <quinq@fifth.space>
Date: Tue, 1 Nov 2016 12:53:53 +0100
Subject: [PATCH] realpath: add fallback processing without /proc

---
 src/misc/realpath.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 63 insertions(+), 2 deletions(-)

diff --git a/src/misc/realpath.c b/src/misc/realpath.c
index 88c849c..b387b59 100644
--- a/src/misc/realpath.c
+++ b/src/misc/realpath.c
@@ -9,13 +9,48 @@
 
 void __procfdname(char *, unsigned);
 
+int mergepaths(char *restrict absolute, const char *restrict relative)
+{
+	char *a = absolute;
+	const char *r = relative;
+
+	/* if relative is absolute, skip absolute */
+	if (*r == '/') {
+		*a = '/';
+		++r;
+	} else {
+		/* slash terminate absolute if needed */
+		for (; *a; ++a);
+		if (*r && (a[-1] != '/')) *a = '/';
+		else --a;
+	}
+
+	/* resolve . and .. */
+	for (; *r; ++r) {
+		if (*r == '.') {
+			if (r[1] == '/' || !r[1]) continue;
+			if (r[1] == '.' && (r[2] == '/' || !r[2])) {
+				while (a > absolute && *--a != '/');
+				continue;
+			}
+		} else if (*r == '/' && *a == '/') continue;
+		*++a = *r;
+	}
+	/* terminate absolute */
+	if (*a == '/' && a > absolute) --a;
+	*++a = 0;
+
+	return a - absolute;
+}
+
 char *realpath(const char *restrict filename, char *restrict resolved)
 {
 	int fd;
 	ssize_t r;
 	struct stat st1, st2;
 	char buf[15+3*sizeof(int)];
-	char tmp[PATH_MAX];
+	char tmp[PATH_MAX], link[PATH_MAX];
+	char *p;
 
 	if (!filename) {
 		errno = EINVAL;
@@ -27,7 +62,7 @@ char *realpath(const char *restrict filename, char *restrict resolved)
 	__procfdname(buf, fd);
 
 	r = readlink(buf, tmp, sizeof tmp - 1);
-	if (r < 0) goto err;
+	if (r < 0) goto noproc;
 	tmp[r] = 0;
 
 	fstat(fd, &st1);
@@ -37,8 +72,34 @@ char *realpath(const char *restrict filename, char *restrict resolved)
 		goto err;
 	}
 
+end:
 	__syscall(SYS_close, fd);
 	return resolved ? strcpy(resolved, tmp) : strdup(tmp);
+
+noproc:
+	if (*filename != '/')
+		if (syscall(SYS_getcwd, tmp, sizeof(tmp)) < 0) goto err;
+
+	/* concatenate cwd and target */
+	r = mergepaths(tmp, filename);
+
+	if (lstat(tmp, &st1) < 0) goto err;
+	/* resolve link chain if any */
+	while (S_ISLNK(st1.st_mode)) {
+		if ((r = readlink(tmp, link, sizeof(link))) < 0) goto err;
+		link[r] = 0;
+
+		/* remove link name */
+		for (p = tmp; *p; ++p);
+		while (p > tmp && *--p != '/');
+		*p = 0;
+
+		/* merge path and link target */
+		mergepaths(tmp, link);
+		if (lstat(tmp, &st1) < 0) goto err;
+	}
+	goto end;
+
 err:
 	__syscall(SYS_close, fd);
 	return 0;
-- 
2.10.2