// program_load(p, program_id)
// Load the code corresponding to program `programnumber` into the process
// `p` and set `p->p_registers.reg_eip` to its entry point. Calls
// `physical_page_alloc` to allocate virtual memory for `p` as required.
// Returns 0 on success and -1 on failure (e.g. out-of-memory).
int program_load(proc* p, int program_id) {
// is this a valid program?
int nprograms = sizeof(ramimages) / sizeof(ramimages[0]);
assert(program_id >= 0 && program_id < nprograms);
elf_header* eh = (elf_header*) ramimages[program_id].begin;
assert(eh->e_magic == ELF_MAGIC);
// load each loadable program segment into memory
elf_program* ph = (elf_program*) ((const uint8_t*) eh + eh->e_phoff);
for (int i = 0; i < eh->e_phnum; ++i)
if (ph[i].p_type == ELF_PTYPE_LOAD)
if (copyseg(p, &ph[i], (const uint8_t*) eh + ph[i].p_offset) < 0)
return -1;
// set the entry point from the ELF header
p->p_registers.reg_eip = eh->e_entry;
return 0;
}
/*
* Create a new process-- the internal version of
* sys fork.
* It returns 1 in the new process.
* How this happens is rather hard to understand.
* The essential fact is that the new process is created
* in such a way that appears to have started executing
* in the same call to newproc as the parent;
* but in fact the code that runs is that of swtch.
* The subtle implication of the returned value of swtch
* (see above) is that this is the value that newproc's
* caller in the new process sees.
*/
newproc()
{
int a1, a2;
struct proc *p, *up;
register struct proc *rpp;
register *rip, n;
p = NULL;
/*
* First, just locate a slot for a process
* and copy the useful info from this process into it.
* The panic "cannot happen" because fork has already
* checked for the existence of a slot.
*/
retry:
mpid++;
if(mpid < 0) {
mpid = 0;
goto retry;
}
for(rpp = &proc[0]; rpp < &proc[NPROC]; rpp++) {
if(rpp->p_stat == NULL && p==NULL)
p = rpp;
if (rpp->p_pid==mpid)
goto retry;
}
if ((rpp = p)==NULL)
panic("no procs");
/*
* make proc entry for new proc
*/
rip = u.u_procp;
up = rip;
rpp->p_stat = SRUN;
rpp->p_flag = SLOAD;
rpp->p_uid = rip->p_uid;
rpp->p_ttyp = rip->p_ttyp;
rpp->p_nice = rip->p_nice;
rpp->p_textp = rip->p_textp;
rpp->p_pid = mpid;
rpp->p_ppid = rip->p_pid;
rpp->p_time = 0;
/*
* make duplicate entries
* where needed
*/
for(rip = &u.u_ofile[0]; rip < &u.u_ofile[NOFILE];)
if((rpp = *rip++) != NULL)
rpp->f_count++;
if((rpp=up->p_textp) != NULL) {
rpp->x_count++;
rpp->x_ccount++;
}
u.u_cdir->i_count++;
/*
* Partially simulate the environment
* of the new process so that when it is actually
* created (by copying) it will look right.
*/
savu(u.u_rsav);
rpp = p;
u.u_procp = rpp;
rip = up;
n = rip->p_size;
a1 = rip->p_addr;
rpp->p_size = n;
a2 = malloc(coremap, n);
/*
* If there is not enough core for the
* new process, swap out the current process to generate the
* copy.
*/
if(a2 == NULL) {
rip->p_stat = SIDL;
rpp->p_addr = a1;
savu(u.u_ssav);
xswap(rpp, 0, 0);
rpp->p_flag =| SSWAP;
rip->p_stat = SRUN;
} else {
/*
* There is core, so just copy.
*/
rpp->p_addr = a2;
while(n--)
copyseg(a1++, a2++);
}
u.u_procp = rip;
return(0);
}
