From 371ab7fa96f8e439f4008c973c37aa44ab6ed81e Mon Sep 17 00:00:00 2001 From: Robert Morris Date: Thu, 1 Sep 2011 13:25:34 -0400 Subject: inaccessible page under the user stack page, to help exec deal w/ too-large args --- exec.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) (limited to 'exec.c') diff --git a/exec.c b/exec.c index dfff3e6..af9e006 100644 --- a/exec.c +++ b/exec.c @@ -49,13 +49,16 @@ exec(char *path, char **argv) iunlockput(ip); ip = 0; - // Allocate a one-page stack at the next page boundary + // Allocate two pages at the next page boundary. + // Make the first inaccessible. + // Use the second as the user stack. sz = PGROUNDUP(sz); - if((sz = allocuvm(pgdir, sz, sz + PGSIZE)) == 0) + if((sz = allocuvm(pgdir, sz, sz + 2*PGSIZE)) == 0) goto bad; + clear_pte_u(pgdir, (char*)(sz-2*PGSIZE)); + sp = sz; // Push argument strings, prepare rest of stack in ustack. - sp = sz; for(argc = 0; argv[argc]; argc++) { if(argc >= MAXARG) goto bad; -- cgit v1.2.3