// Open a directory for scanning.
// For simplicity, DIR is simply a filedesc like other file descriptors,
// except we interpret fd->ofs as an inode number for scanning,
// instead of as a byte offset as in a regular file.
DIR *opendir(const char *path)
{
filedesc *fd = filedesc_open(NULL, path, O_RDONLY, 0);
if (fd == NULL)
return NULL;
// Make sure it's a directory
assert(fileino_exists(fd->ino));
fileinode *fi = &files->fi[fd->ino];
if (!S_ISDIR(fi->mode)) {
filedesc_close(fd);
errno = ENOTDIR;
return NULL;
}
return fd;
}
int closedir(DIR *dir)
{
filedesc_close(dir);
return 0;
}
int
close(int fn)
{
filedesc_close(&files->fd[fn]);
return 0;
}
int
fclose(FILE *fd)
{
filedesc_close(fd);
return 0;
}
int
exec_readelf(const char *path)
{
// We'll load the ELF image into a scratch area in our address space.
sys_get(SYS_ZERO, 0, NULL, NULL, (void*)VM_SCRATCHLO, EXEMAX);
// Open the ELF image to load.
filedesc *fd = filedesc_open(NULL, path, O_RDONLY, 0);
if (fd == NULL)
return -1;
void *imgdata = FILEDATA(fd->ino);
size_t imgsize = files->fi[fd->ino].size;
// Make sure it looks like an ELF image.
elfhdr *eh = imgdata;
if (imgsize < sizeof(*eh) || eh->e_magic != ELF_MAGIC) {
warn("exec_readelf: ELF header not found");
goto err;
}
// Load each program segment into the scratch area
proghdr *ph = imgdata + eh->e_phoff;
proghdr *eph = ph + eh->e_phnum;
if (imgsize < (void*)eph - imgdata) {
warn("exec_readelf: ELF program header truncated");
goto err;
}
for (; ph < eph; ph++) {
if (ph->p_type != ELF_PROG_LOAD)
continue;
// The executable should fit in the first 4MB of user space.
intptr_t valo = ph->p_va;
intptr_t vahi = valo + ph->p_memsz;
if (valo < VM_USERLO || valo > VM_USERLO+EXEMAX ||
vahi < valo || vahi > VM_USERLO+EXEMAX) {
warn("exec_readelf: executable image too large "
"(%d bytes > %d max)", vahi-valo, EXEMAX);
goto err;
}
// Map all pages the segment touches in our scratch region.
// They've already been zeroed by the SYS_ZERO above.
intptr_t scratchofs = VM_SCRATCHLO - VM_USERLO;
intptr_t pagelo = ROUNDDOWN(valo, PAGESIZE);
intptr_t pagehi = ROUNDUP(vahi, PAGESIZE);
sys_get(SYS_PERM | SYS_READ | SYS_WRITE, 0, NULL, NULL,
(void*)pagelo + scratchofs, pagehi - pagelo);
// Initialize the file-loaded part of the ELF image.
// (We could use copy-on-write if SYS_COPY
// supports copying at arbitrary page boundaries.)
intptr_t filelo = ph->p_offset;
intptr_t filehi = filelo + ph->p_filesz;
if (filelo < 0 || filelo > imgsize
|| filehi < filelo || filehi > imgsize) {
warn("exec_readelf: loaded section out of bounds");
goto err;
}
memcpy((void*)valo + scratchofs, imgdata + filelo,
filehi - filelo);
// Finally, remove write permissions on read-only segments.
if (!(ph->p_flags & ELF_PROG_FLAG_WRITE))
sys_get(SYS_PERM | SYS_READ, 0, NULL, NULL,
(void*)pagelo + scratchofs, pagehi - pagelo);
}
// Copy the ELF image into its correct position in child 0.
sys_put(SYS_COPY, 0, NULL, (void*)VM_SCRATCHLO,
(void*)VM_USERLO, EXEMAX);
// The new program should have the same entrypoint as we do!
if (eh->e_entry != (intptr_t)start) {
warn("exec_readelf: executable has a different start address");
goto err;
}
filedesc_close(fd); // Done with the ELF file
return 0;
err:
filedesc_close(fd);
return -1;
}
