int
execv(const char *path, char *const argv[])
{
// We'll build the new program in child 0,
// which never represents a forked child since 0 is an invalid pid.
// First clear out the new program's entire address space.
sys_put(SYS_ZERO, 0, NULL, NULL, (void*)VM_USERLO, VM_USERHI-VM_USERLO);
// Load the ELF executable into child 0.
if (exec_readelf(path) < 0)
return -1;
// Setup child 0's stack with the argument array.
intptr_t esp = exec_copyargs(argv);
// Copy our Unix file system and process state into the child.
sys_put(SYS_COPY, 0, NULL, (void*)VM_FILELO, (void*)VM_FILELO,
VM_FILEHI-VM_FILELO);
// Copy child 0's entire memory state onto ours
// and start the new program. See lib/entry.S for details.
exec_start(esp);
}
intptr_t
exec_copyargs(char *const argv[])
{
// Give the process a nice big 4MB, zero-filled stack.
sys_get(SYS_ZERO | SYS_PERM | SYS_READ | SYS_WRITE, 0, NULL,
NULL, (void*)VM_SCRATCHLO, PTSIZE);
#if SOL >= 4
// How many arguments?
int argc;
for (argc = 0; argv[argc] != NULL; argc++)
;
// Make room for the argv array
intptr_t esp = VM_STACKHI;
intptr_t scratchofs = VM_SCRATCHLO - (VM_STACKHI-PTSIZE);
esp -= (argc+1) * sizeof(intptr_t); // room for arguments plus NULL
intptr_t dargv = esp;
// Copy the argument strings
int i;
for (i = 0; i < argc; i++) {
int len = strlen(argv[i]);
esp -= len+1;
strcpy((void*)esp + scratchofs, argv[i]);
((intptr_t*)(dargv + scratchofs))[i] = esp;
}
esp &= ~3; // get esp word-aligned again
// Push the arguments to main()
esp -= 4; *(intptr_t*)(esp + scratchofs) = dargv;
esp -= 4; *(intptr_t*)(esp + scratchofs) = argc;
#else // ! SOL >= 4
// Lab 4: insert your code here to copy our command-line arguments
// onto the new process's stack, taking into account the fact that
// the stack area is mapped at VM_SCRATCHLO to VM_SCRATCHLO+PTSIZE
// in _our_ address space while we're copying the arguments,
// but the pointers we're writing into this space will be
// interpreted by the newly executed process,
// where the stack will be mapped from VM_STACKHI-PTSIZE to VM_STACKHI.
warn("exec_copyargs not implemented yet");
intptr_t esp = VM_STACKHI; // no arguments - fix this.
#endif // ! SOL >= 4
// Copy the stack into its correct position in child 0.
sys_put(SYS_COPY, 0, NULL, (void*)VM_SCRATCHLO,
(void*)VM_STACKHI-PTSIZE, PTSIZE);
return esp;
}
void
proc_check(void)
{
// Spawn 2 child processes, executing on statically allocated stacks.
cprintf("in proc_check()\n");
int i;
for (i = 0; i < 4; i++) {
// Setup register state for child
uint32_t *esp = (uint32_t*) &child_stack[i][PAGESIZE];
*--esp = i; // push argument to child() function
*--esp = 0; // fake return address
child_state.tf.eip = (uint32_t) child;
child_state.tf.esp = (uint32_t) esp;
// Use PUT syscall to create each child,
// but only start the first 2 children for now.
cprintf("spawning child %d\n", i);
sys_put(SYS_REGS | (i < 2 ? SYS_START : 0), i, &child_state,
NULL, NULL, 0);
}
cprintf("proc_check() created childs\n");
// Wait for both children to complete.
// This should complete without preemptive scheduling
// when we're running on a 2-processor machine.
for (i = 0; i < 2; i++) {
cprintf("waiting for child %d\n", i);
sys_get(SYS_REGS, i, &child_state, NULL, NULL, 0);
}
cprintf("proc_check() 2-child test succeeded\n");
// (Re)start all four children, and wait for them.
// This will require preemptive scheduling to complete
// if we have less than 4 CPUs.
cprintf("proc_check: spawning 4 children\n");
for (i = 0; i < 4; i++) {
cprintf("spawning child %d\n", i);
sys_put(SYS_START, i, NULL, NULL, NULL, 0);
}
// Wait for all 4 children to complete.
for (i = 0; i < 4; i++)
sys_get(0, i, NULL, NULL, NULL, 0);
cprintf("proc_check() 4-child test succeeded\n");
// Now do a trap handling test using all 4 children -
// but they'll _think_ they're all child 0!
// (We'll lose the register state of the other children.)
i = 0;
sys_get(SYS_REGS, i, &child_state, NULL, NULL, 0);
// get child 0's state
assert(recovargs == NULL);
do {
sys_put(SYS_REGS | SYS_START, i, &child_state, NULL, NULL, 0);
sys_get(SYS_REGS, i, &child_state, NULL, NULL, 0);
if (recovargs) { // trap recovery needed
trap_check_args *args = recovargs;
cprintf("recover from trap %d\n",
child_state.tf.trapno);
child_state.tf.eip = (uint32_t) args->reip;
args->trapno = child_state.tf.trapno;
} else
assert(child_state.tf.trapno == T_SYSCALL);
i = (i+1) % 4; // rotate to next child proc
} while (child_state.tf.trapno != T_SYSCALL);
assert(recovargs == NULL);
cprintf("proc_check() trap reflection test succeeded\n");
cprintf("proc_check() succeeded!\n");
}
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;
}
