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authorRoland McGrath <roland@redhat.com>2008-04-10 18:37:38 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2008-04-10 20:28:26 -0400
commit54a015104136974262afa4b8ddd943ea70dec8a2 (patch)
tree713f0c1f4d0afe62e5c568a424e309f70388cf7f /include/linux/linkage.h
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 'include/linux/linkage.h')
-rw-r--r--include/linux/linkage.h4
1 files changed, 2 insertions, 2 deletions
diff --git a/include/linux/linkage.h b/include/linux/linkage.h
index 0592936344c4..fe2a39c489b6 100644
--- a/include/linux/linkage.h
+++ b/include/linux/linkage.h
@@ -17,8 +17,8 @@
17# define asmregparm 17# define asmregparm
18#endif 18#endif
19 19
20#ifndef prevent_tail_call 20#ifndef asmlinkage_protect
21# define prevent_tail_call(ret) do { } while (0) 21# define asmlinkage_protect(n, ret, args...) do { } while (0)
22#endif 22#endif
23 23
24#ifndef __ALIGN 24#ifndef __ALIGN