Edit exec.
Do not commit to new memory image until nothing can go wrong, avoiding bad2 case. Be sure to allocate enough stack space for argv. Load executable before initializing stack, to keep ELF loops together. Make argv loop clearer.
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e79b16598c
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629c1fe743
1 changed files with 57 additions and 75 deletions
132
exec.c
132
exec.c
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@ -1,44 +1,35 @@
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#include "types.h"
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#include "stat.h"
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#include "param.h"
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#include "mmu.h"
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#include "proc.h"
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#include "defs.h"
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#include "x86.h"
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#include "traps.h"
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#include "syscall.h"
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#include "spinlock.h"
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#include "buf.h"
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#include "fs.h"
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#include "fsvar.h"
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#include "elf.h"
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#include "file.h"
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#include "fcntl.h"
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int
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exec(char *path, char **argv)
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{
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uint sz, sp, p1, p2;
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int i, nargs, argbytes, len, off;
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struct inode *ip;
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char *mem, *s, *last;
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int i, argc, arglen, len, off;
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uint sz, sp, argp;
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struct elfhdr elf;
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struct inode *ip;
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struct proghdr ph;
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char *mem;
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char *s, *last;
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sz = 0;
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mem = 0;
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if((ip = namei(path)) == 0)
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return -1;
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ilock(ip);
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// Compute memory size of new process.
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mem = 0;
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sz = 0;
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// Program segments.
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if(readi(ip, (char*)&elf, 0, sizeof(elf)) < sizeof(elf))
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goto bad;
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if(elf.magic != ELF_MAGIC)
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goto bad;
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for(i=0, off=elf.phoff; i<elf.phnum; i++, off+=sizeof(ph)){
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if(readi(ip, (char*)&ph, off, sizeof(ph)) != sizeof(ph))
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goto bad;
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@ -48,77 +39,73 @@ exec(char *path, char **argv)
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goto bad;
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sz += ph.memsz;
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}
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// Arguments.
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arglen = 0;
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for(argc=0; argv[argc]; argc++)
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arglen += strlen(argv[i]) + 1;
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arglen = (arglen+3) & ~3;
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sz += arglen + 4*(argc+1);
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sz += 4096 - (sz % 4096);
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sz += 4096;
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// Stack.
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sz += PAGE;
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// Allocate program memory.
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sz = (sz+PAGE-1) & ~(PAGE-1);
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mem = kalloc(sz);
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if(mem == 0)
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goto bad;
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memset(mem, 0, sz);
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argbytes = 0;
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for(i = 0; argv[i]; i++){
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len = strlen(argv[i]);
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argbytes += len + 1;
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// Load program into memory.
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for(i=0, off=elf.phoff; i<elf.phnum; i++, off+=sizeof(ph)){
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if(readi(ip, (char*)&ph, off, sizeof(ph)) != sizeof(ph))
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goto bad;
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if(ph.type != ELF_PROG_LOAD)
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continue;
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if(ph.va + ph.memsz > sz)
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goto bad;
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if(readi(ip, mem + ph.va, ph.offset, ph.filesz) != ph.filesz)
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goto bad;
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memset(mem + ph.va + ph.filesz, 0, ph.memsz - ph.filesz);
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}
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nargs = i;
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iunlockput(ip);
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// Initialize stack.
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sp = sz;
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argp = sz - arglen;
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// argn\0
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// ...
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// arg0\0
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// 0
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// ptr to argn
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// ...
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// 12: ptr to arg0
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// 8: argv (points to ptr to arg0)
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// 4: argc
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// 0: fake return pc
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sp = sz - argbytes - (nargs+1)*4 - 4 - 4 - 4;
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*(uint*)(mem + sp) = 0xffffffff;
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*(uint*)(mem + sp + 4) = nargs;
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*(uint*)(mem + sp + 8) = (uint)(sp + 12);
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p1 = sp + 12;
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p2 = sp + 12 + (nargs + 1) * 4;
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for(i = 0; i < nargs; i++){
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len = strlen(argv[i]);
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memmove(mem + p2, argv[i], len + 1);
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*(uint*)(mem + p1) = p2;
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p1 += 4;
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p2 += len + 1;
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// Copy argv strings and pointers to stack.
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*(uint*)(mem+argp + 4*argc) = 0; // argv[argc]
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for(i=argc-1; i>=0; i--){
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len = strlen(argv[i]) + 1;
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sp -= len;
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memmove(mem+sp, argv[i], len);
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*(uint*)(mem+argp + 4*i) = sp; // argv[i]
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}
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*(uint*)(mem + p1) = 0;
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// Save name for debugging.
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// Stack frame for main(argc, argv), below arguments.
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sp = argp;
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sp -= 4;
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*(uint*)(mem+sp) = argp;
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sp -= 4;
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*(uint*)(mem+sp) = argc;
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sp -= 4;
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*(uint*)(mem+sp) = 0xffffffff; // fake return pc
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// Save program name for debugging.
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for(last=s=path; *s; s++)
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if(*s == '/')
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last = s+1;
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safestrcpy(cp->name, last, sizeof(cp->name));
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// commit to the new image.
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// Commit to the new image.
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kfree(cp->mem, cp->sz);
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cp->sz = sz;
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cp->mem = mem;
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mem = 0;
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for(i=0, off=elf.phoff; i<elf.phnum; i++, off+=sizeof(ph)){
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if(readi(ip, (char*)&ph, off, sizeof(ph)) != sizeof(ph))
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goto bad2;
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if(ph.type != ELF_PROG_LOAD)
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continue;
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if(ph.va + ph.memsz > sz)
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goto bad2;
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if(readi(ip, cp->mem + ph.va, ph.offset, ph.filesz) != ph.filesz)
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goto bad2;
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memset(cp->mem + ph.va + ph.filesz, 0, ph.memsz - ph.filesz);
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}
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iunlockput(ip);
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cp->tf->eip = elf.entry;
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cp->sz = sz;
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cp->tf->eip = elf.entry; // main
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cp->tf->esp = sp;
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setupsegs(cp);
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return 0;
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bad:
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@ -126,9 +113,4 @@ exec(char *path, char **argv)
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kfree(mem, sz);
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iunlockput(ip);
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return -1;
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bad2:
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iunlockput(ip);
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proc_exit();
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return 0;
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}
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