xv6-cs450/exec.c

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#include "types.h"
#include "param.h"
#include "mmu.h"
#include "proc.h"
#include "defs.h"
#include "x86.h"
#include "elf.h"
int
exec(char *path, char **argv)
{
char *mem, *s, *last;
int i, argc, arglen, len, off;
uint sz, sp, spbottom, argp;
struct elfhdr elf;
struct inode *ip;
struct proghdr ph;
pde_t *pgdir, *oldpgdir;
pgdir = 0;
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sz = 0;
if((ip = namei(path)) == 0)
return -1;
ilock(ip);
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// Check ELF header
if(readi(ip, (char*)&elf, 0, sizeof(elf)) < sizeof(elf))
goto bad;
if(elf.magic != ELF_MAGIC)
goto bad;
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if(!(pgdir = setupkvm()))
goto bad;
// Load program into memory.
for(i=0, off=elf.phoff; i<elf.phnum; i++, off+=sizeof(ph)){
if(readi(ip, (char*)&ph, off, sizeof(ph)) != sizeof(ph))
goto bad;
if(ph.type != ELF_PROG_LOAD)
continue;
if(ph.memsz < ph.filesz)
goto bad;
if(!(sz = allocuvm(pgdir, sz, ph.va + ph.memsz)))
goto bad;
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if(!loaduvm(pgdir, (char *)ph.va, ip, ph.offset, ph.filesz))
goto bad;
}
iunlockput(ip);
// Allocate and initialize stack at sz
sz = spbottom = PGROUNDUP(sz);
if(!(sz = allocuvm(pgdir, sz, sz + PGSIZE)))
goto bad;
mem = uva2ka(pgdir, (char *)spbottom);
arglen = 0;
for(argc=0; argv[argc]; argc++)
arglen += strlen(argv[argc]) + 1;
arglen = (arglen+3) & ~3;
sp = sz;
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argp = sz - arglen - 4*(argc+1);
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// XXX rtm: does the following code work if the
// arguments &c do not fit in one page?
// Copy argv strings and pointers to stack.
*(uint*)(mem+argp-spbottom + 4*argc) = 0; // argv[argc]
for(i=argc-1; i>=0; i--){
len = strlen(argv[i]) + 1;
sp -= len;
memmove(mem+sp-spbottom, argv[i], len);
*(uint*)(mem+argp-spbottom + 4*i) = sp; // argv[i]
}
// Stack frame for main(argc, argv), below arguments.
sp = argp;
sp -= 4;
*(uint*)(mem+sp-spbottom) = argp;
sp -= 4;
*(uint*)(mem+sp-spbottom) = argc;
sp -= 4;
*(uint*)(mem+sp-spbottom) = 0xffffffff; // fake return pc
// Save program name for debugging.
for(last=s=path; *s; s++)
if(*s == '/')
last = s+1;
safestrcpy(proc->name, last, sizeof(proc->name));
// Commit to the user image.
oldpgdir = proc->pgdir;
proc->pgdir = pgdir;
proc->sz = sz;
proc->tf->eip = elf.entry; // main
proc->tf->esp = sp;
switchuvm(proc);
freevm(oldpgdir);
return 0;
bad:
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if(pgdir) freevm(pgdir);
iunlockput(ip);
return -1;
}