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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 /arch
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 'arch')
-rw-r--r--arch/x86/kernel/tls.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/x86/kernel/tls.c b/arch/x86/kernel/tls.c
index 022bcaa3b42..ab6bf375a30 100644
--- a/arch/x86/kernel/tls.c
+++ b/arch/x86/kernel/tls.c
@@ -92,7 +92,7 @@ int do_set_thread_area(struct task_struct *p, int idx,
asmlinkage int sys_set_thread_area(struct user_desc __user *u_info)
{
int ret = do_set_thread_area(current, -1, u_info, 1);
- prevent_tail_call(ret);
+ asmlinkage_protect(1, ret, u_info);
return ret;
}
@@ -142,7 +142,7 @@ int do_get_thread_area(struct task_struct *p, int idx,
asmlinkage int sys_get_thread_area(struct user_desc __user *u_info)
{
int ret = do_get_thread_area(current, -1, u_info);
- prevent_tail_call(ret);
+ asmlinkage_protect(1, ret, u_info);
return ret;
}