path: root/kernel/exit.c
diff options
authorRoland McGrath <roland@redhat.com>2008-04-10 15:37:38 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-04-10 17:28:26 -0700
commit54a015104136974262afa4b8ddd943ea70dec8a2 (patch)
tree713f0c1f4d0afe62e5c568a424e309f70388cf7f /kernel/exit.c
parent783e391b7b5b273cd20856d8f6f4878da8ec31b3 (diff)
asmlinkage_protect replaces prevent_tail_call
The prevent_tail_call() macro works around the problem of the compiler clobbering argument words on the stack, which for asmlinkage functions is the caller's (user's) struct pt_regs. The tail/sibling-call optimization is not the only way that the compiler can decide to use stack argument words as scratch space, which we have to prevent. Other optimizations can do it too. Until we have new compiler support to make "asmlinkage" binding on the compiler's own use of the stack argument frame, we have work around all the manifestations of this issue that crop up. More cases seem to be prevented by also keeping the incoming argument variables live at the end of the function. This makes their original stack slots attractive places to leave those variables, so the compiler tends not clobber them for something else. It's still no guarantee, but it handles some observed cases that prevent_tail_call() did not. Signed-off-by: Roland McGrath <roland@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/exit.c')
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/exit.c b/kernel/exit.c
index 53872bf993f..073005b1cfb 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1608,7 +1608,7 @@ asmlinkage long sys_waitid(int which, pid_t upid,
/* avoid REGPARM breakage on x86: */
- prevent_tail_call(ret);
+ asmlinkage_protect(5, ret, which, upid, infop, options, ru);
return ret;
@@ -1640,7 +1640,7 @@ asmlinkage long sys_wait4(pid_t upid, int __user *stat_addr,
/* avoid REGPARM breakage on x86: */
- prevent_tail_call(ret);
+ asmlinkage_protect(4, ret, upid, stat_addr, options, ru);
return ret;