Add build system scaffolding and libc headers

1 files changed, 140 insertions, 0 deletions

diff --git a/lib/libc/dirent/readdir_r.c b/lib/libc/dirent/readdir_r.c
new file mode 100644
index 00000000..9d8bf49b
--- /dev/null
+++ b/lib/libc/dirent/readdir_r.c
@@ -0,0 +1,140 @@
+/* Maintainer: <contact@bellrise.net> */
+
+#include <__dirent.h>
+#include <errno.h>
+#include <dirent.h>
+#include <syscall.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <string.h>
+#include <stddef.h>
+
+#include <stdio.h>
+
+int readdir_r(DIR *restrict dirp, struct dirent *restrict entry,
+	      struct dirent **restrict result)
+{
+	struct linux_dirent64 *ldir = (void *)dirp->buffer;
+	ssize_t nread;
+	int ret;
+
+	if (dirp == NULL || entry == NULL || result == NULL) {
+		return EINVAL;
+	}
+
+	/* Clear the result entry to prevent garbage data */
+	memset(entry, 0, sizeof(*entry));
+
+	if (dirp->cached) {
+		ldir = (void *)(dirp->buffer + dirp->offset);
+
+		/* Validate buffer bounds */
+		if (dirp->offset >= sizeof(dirp->buffer) ||
+		    dirp->offset + sizeof(struct linux_dirent64) >
+			    sizeof(dirp->buffer)) {
+			dirp->cached = 0;
+			*result = NULL;
+			return 0;
+		}
+
+		/* Validate record length */
+		if (ldir->d_reclen <
+			    offsetof(struct linux_dirent64, d_name) + 1 ||
+		    dirp->offset + ldir->d_reclen > sizeof(dirp->buffer) ||
+		    ldir->d_reclen == 0) {
+			dirp->cached = 0;
+			*result = NULL;
+			return 0;
+		}
+
+		entry->d_ino = ldir->d_ino;
+
+		/* Calculate available space for name */
+		size_t max_name_len = ldir->d_reclen -
+				      offsetof(struct linux_dirent64, d_name);
+		if (max_name_len > sizeof(entry->d_name) - 1) {
+			max_name_len = sizeof(entry->d_name) - 1;
+		}
+
+		/* Find actual string length, bounded by available space */
+		size_t name_len = 0;
+		while (name_len < max_name_len &&
+		       ldir->d_name[name_len] != '\0') {
+			name_len++;
+		}
+
+		memcpy(entry->d_name, ldir->d_name, name_len);
+		entry->d_name[name_len] = '\0';
+
+		dirp->cached--;
+		dirp->offset += ldir->d_reclen;
+		*result = entry;
+		return 0;
+	}
+
+	/* Clear cached entries and reset offset */
+	dirp->cached = 0;
+	dirp->offset = 0;
+
+	ret = syscall(getdents64, dirp->fildes, dirp->buffer,
+		      sizeof(dirp->buffer));
+	if (ret < 0)
+		return errno;
+
+	if (ret == 0) {
+		*result = NULL;
+		return 0;
+	}
+
+	/* Read first entry from buffer. */
+	nread = ret;
+
+	/* Validate first entry bounds */
+	if (nread < sizeof(struct linux_dirent64) ||
+	    ldir->d_reclen < offsetof(struct linux_dirent64, d_name) + 1 ||
+	    ldir->d_reclen > nread || ldir->d_reclen == 0) {
+		*result = NULL;
+		return EINVAL;
+	}
+
+	dirp->offset = ldir->d_reclen;
+	entry->d_ino = ldir->d_ino;
+
+	/* Calculate available space for name */
+	size_t max_name_len =
+		ldir->d_reclen - offsetof(struct linux_dirent64, d_name);
+	if (max_name_len > sizeof(entry->d_name) - 1) {
+		max_name_len = sizeof(entry->d_name) - 1;
+	}
+
+	/* Find actual string length, bounded by available space */
+	size_t name_len = 0;
+	while (name_len < max_name_len && ldir->d_name[name_len] != '\0') {
+		name_len++;
+	}
+
+	memcpy(entry->d_name, ldir->d_name, name_len);
+	entry->d_name[name_len] = '\0';
+	*result = entry;
+
+	/* Count the amount of remaining entries we have cached from getdents.
+	 */
+	for (ssize_t buffer_offset = ldir->d_reclen; buffer_offset < nread;) {
+		struct linux_dirent64 *next_ldir =
+			(void *)(dirp->buffer + buffer_offset);
+
+		/* Validate entry bounds to prevent infinite loops */
+		if (buffer_offset + sizeof(struct linux_dirent64) > nread ||
+		    next_ldir->d_reclen <
+			    offsetof(struct linux_dirent64, d_name) + 1 ||
+		    buffer_offset + next_ldir->d_reclen > nread ||
+		    next_ldir->d_reclen == 0) {
+			break;
+		}
+
+		buffer_offset += next_ldir->d_reclen;
+		dirp->cached++;
+	}
+
+	return 0;
+}