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Diffstat (limited to 'exec.c')
-rw-r--r--exec.c28
1 files changed, 14 insertions, 14 deletions
diff --git a/exec.c b/exec.c
index 4c34a51..c854aae 100644
--- a/exec.c
+++ b/exec.c
@@ -13,7 +13,7 @@ exec(char *path, char **argv)
{
char *s, *last;
int i, off;
- uint64 argc, sz, sp, ustack[3+MAXARG+1];
+ uint64 argc, sz, sp, ustack[MAXARG+1];
struct elfhdr elf;
struct inode *ip;
struct proghdr ph;
@@ -71,24 +71,24 @@ exec(char *path, char **argv)
for(argc = 0; argv[argc]; argc++) {
if(argc >= MAXARG)
goto bad;
- sp = (sp - (strlen(argv[argc]) + 1)) & ~(sizeof(uint64)-1);
+ sp -= strlen(argv[argc]) + 1;
+ sp -= sp % 16; // riscv sp must be 16-byte aligned
if(copyout(pagetable, sp, argv[argc], strlen(argv[argc]) + 1) < 0)
goto bad;
- ustack[3+argc] = sp;
+ ustack[argc] = sp;
}
- ustack[3+argc] = 0;
+ ustack[argc] = 0;
- ustack[0] = 0xffffffff; // fake return PC
- ustack[1] = argc;
- ustack[2] = sp - (argc+1)*sizeof(uint64); // argv pointer
+ // push the array of argv[] pointers.
+ sp -= (argc+1) * sizeof(uint64);
+ sp -= sp % 16;
+ if(copyout(pagetable, sp, (char *)ustack, (argc+1)*sizeof(uint64)) < 0)
+ goto bad;
// arguments to user main(argc, argv)
- p->tf->a0 = argc;
- p->tf->a1 = sp - (argc+1)*sizeof(uint64);
-
- sp -= (3+argc+1) * sizeof(uint64);
- if(copyout(pagetable, sp, (char *)ustack, (3+argc+1)*sizeof(uint64)) < 0)
- goto bad;
+ // argc is returned via the system call return
+ // value, which goes in a0.
+ p->tf->a1 = sp;
// Save program name for debugging.
for(last=s=path; *s; s++)
@@ -103,7 +103,7 @@ exec(char *path, char **argv)
p->tf->epc = elf.entry; // initial program counter = main
p->tf->sp = sp; // initial stack pointer
proc_freepagetable(oldpagetable, oldsz);
- return 0;
+ return argc; // this ends up in a0, the first argument to main(argc, argv)
bad:
if(pagetable)