xv6-65oo2/kernel/exec.c

167 lines
3.8 KiB
C

#include "types.h"
#include "param.h"
#include "memlayout.h"
#include "riscv.h"
#include "spinlock.h"
#include "proc.h"
#include "defs.h"
#include "elf.h"
static int loadseg(pde_t *, uint64, struct inode *, uint, uint);
int flags2perm(int flags)
{
int perm = 0;
if(flags & 0x1)
perm = PTE_X;
if(flags & 0x2)
perm |= PTE_W;
return perm;
}
int
exec(char *path, char **argv)
{
char *s, *last;
int i, off;
uint64 argc, sz = 0, sp, ustack[MAXARG], stackbase;
struct elfhdr elf;
struct inode *ip;
struct proghdr ph;
pagetable_t pagetable = 0, oldpagetable;
struct proc *p = myproc();
begin_op();
if((ip = namei(path)) == 0){
end_op();
return -1;
}
ilock(ip);
// Check ELF header
if(readi(ip, 0, (uint64)&elf, 0, sizeof(elf)) != sizeof(elf))
goto bad;
if(elf.magic != ELF_MAGIC)
goto bad;
if((pagetable = proc_pagetable(p)) == 0)
goto bad;
// Load program into memory.
for(i=0, off=elf.phoff; i<elf.phnum; i++, off+=sizeof(ph)){
if(readi(ip, 0, (uint64)&ph, off, sizeof(ph)) != sizeof(ph))
goto bad;
if(ph.type != ELF_PROG_LOAD)
continue;
if(ph.memsz < ph.filesz)
goto bad;
if(ph.vaddr + ph.memsz < ph.vaddr)
goto bad;
if(ph.vaddr % PGSIZE != 0)
goto bad;
uint64 sz1;
if((sz1 = uvmalloc(pagetable, sz, ph.vaddr + ph.memsz, flags2perm(ph.flags))) == 0)
goto bad;
sz = sz1;
if(loadseg(pagetable, ph.vaddr, ip, ph.off, ph.filesz) < 0)
goto bad;
}
iunlockput(ip);
end_op();
ip = 0;
p = myproc();
uint64 oldsz = p->sz;
// Allocate two pages at the next page boundary.
// Make the first inaccessible as a stack guard.
// Use the second as the user stack.
sz = PGROUNDUP(sz);
uint64 sz1;
if((sz1 = uvmalloc(pagetable, sz, sz + 2*PGSIZE, PTE_W)) == 0)
goto bad;
sz = sz1;
uvmclear(pagetable, sz-2*PGSIZE);
sp = sz;
stackbase = sp - PGSIZE;
// Push argument strings, prepare rest of stack in ustack.
for(argc = 0; argv[argc]; argc++) {
if(argc >= MAXARG)
goto bad;
sp -= strlen(argv[argc]) + 1;
sp -= sp % 16; // riscv sp must be 16-byte aligned
if(sp < stackbase)
goto bad;
if(copyout(pagetable, sp, argv[argc], strlen(argv[argc]) + 1) < 0)
goto bad;
ustack[argc] = sp;
}
ustack[argc] = 0;
// push the array of argv[] pointers.
sp -= (argc+1) * sizeof(uint64);
sp -= sp % 16;
if(sp < stackbase)
goto bad;
if(copyout(pagetable, sp, (char *)ustack, (argc+1)*sizeof(uint64)) < 0)
goto bad;
// arguments to user main(argc, argv)
// argc is returned via the system call return
// value, which goes in a0.
p->trapframe->a1 = sp;
// Save program name for debugging.
for(last=s=path; *s; s++)
if(*s == '/')
last = s+1;
safestrcpy(p->name, last, sizeof(p->name));
// Commit to the user image.
oldpagetable = p->pagetable;
p->pagetable = pagetable;
p->sz = sz;
p->trapframe->epc = elf.entry; // initial program counter = main
p->trapframe->sp = sp; // initial stack pointer
proc_freepagetable(oldpagetable, oldsz);
return argc; // this ends up in a0, the first argument to main(argc, argv)
bad:
if(pagetable)
proc_freepagetable(pagetable, sz);
if(ip){
iunlockput(ip);
end_op();
}
return -1;
}
// Load a program segment into pagetable at virtual address va.
// va must be page-aligned
// and the pages from va to va+sz must already be mapped.
// Returns 0 on success, -1 on failure.
static int
loadseg(pagetable_t pagetable, uint64 va, struct inode *ip, uint offset, uint sz)
{
uint i, n;
uint64 pa;
for(i = 0; i < sz; i += PGSIZE){
pa = walkaddr(pagetable, va + i);
if(pa == 0)
panic("loadseg: address should exist");
if(sz - i < PGSIZE)
n = sz - i;
else
n = PGSIZE;
if(readi(ip, 0, (uint64)pa, offset+i, n) != n)
return -1;
}
return 0;
}